SHOP PRODUCTS
Houzz Logo Print
deziree_worster

energy/heat efficient floors over radiant in slab

deziree_worster
5 years ago
we are building a 2400 square foot one level home on slab with in-floor radiant heat. The point of this house is energy efficiency. we initially we're going with wood look tile throughout. now, as we are on a time constraint, we've been looking into luxury vinyl planks. what do you think the difference will be in terms of utilizing the efficiency of radiant with each floor choice?

Comments (50)

  • PRO
    Oak & Broad
    5 years ago

    I'm sure someone has done a research study on this before. Did you Google search it? Here is a full article I found on Google.

  • PRO
    Springtime Builders
    5 years ago
    last modified: 5 years ago

    If you have the right amount of insulation under your slab, it shouldn't really matter. Probably a good case for extra sub-slab R-value with carpeting but carpet is a poor choice for other reasons.

    That article opens with the classic radiant floor misconceptions. A new home, built to international code levels of air-sealing and insulation should not feel the warmth of a radiant floor. Except on the coldest days of the year, the floor should be at room temperature. If you can feel the warmth, it indicates a poorly built home for energy efficiency.

    If the point for the radiant floors is energy efficiency, then they are a fine choice. I need to update my radiant floor heating blog to include the possibility of using them to help the expanding renewable energy electric grid. By using demand controls from the electric utility or a timer, a radiant floor makes a good battery to help with the duck curve. You could charge the floor slab or hydronic storage tank during times of cheap excess renewable generation and turn it off at night or times of high electricity prices.

    Comfort is more debatable. Due to thermostat response delay, radiant floors can be less comfortable than forced air systems.

    The biggest issue is typically costs. If the house is planning no AC, then radiant can be a better choice. Heat pumps, even in cold climates, can be economical to heat with so adding a seperate radiant system is highly questionable economically, if the plan includes AC.

  • Related Discussions

    On-Slab Radiant Floor Heating Feasiblity

    Q

    Comments (2)
    What you're proposing is certainly feasible using your existing boiler and some sort of 3 or 4 way mixing valve or assembly. Your floor would have to be isolated from the existing slab and you would not benefit from a thermal mass. However, you may have faster reaction times. Keep in mind that pipe spacing is related to water temperature so make sure of your design before starting and ordering materials. Do consult with a radiant in-floor specialist that understands hydronic boilers as well - you don't want surprises! SR
    ...See More

    slab for flooring and energy efficiency?

    Q

    Comments (12)
    I lived in a house with a finished concrete slab as the main flooring for about 5 years. Overall, I liked it a lot, especially the look. However, I relate to the concerns mentioned by the previous posters. I lived in the northeast, but my floor would still "sweat" a few times during the summer. Very weird experience, but rare enough to not be a huge issue for me. It is indeed a very hard surface, which can be hard on our body, especially if you have any joint issues. Regarding your question about efficiency, my house was definitely very efficient. Much more so than the old farmhouse on a 200 year old basement I have now. If you put a significant amount of insulation under the slab, you will have a very efficient home. The typical passivhaus approach, the most rigorous efficiency standard right now, is typically done on a slab because it is much easier to air seal and insulate than is a basement or crawl space. We had radiant heat in our slab. Because the slab is a tremendous thermal mass, this is a very efficient approach if you will be keeping the house heated throughout the winter. For a second home, this option can be annoying because it takes the slab quite a while to come up to temperature. I had this issue because I was traveling a lot at the time and would turn the heat down. When I'd come home, it would take about 12 hours to bring the house temperature up just using the slab heat. However, we didn't have insulation in our slab because it was a converted barn with a repurposed slab. YMMV if you have insulation underneath.
    ...See More

    What floor covering do you have over your radiant heat?

    Q

    Comments (8)
    We used an epoxy paint with the paint flecks so as to resemble terrazzo over our radiant heated shop floor that we put in. Ourselves. Embedded in the slab. We wanted the best transfer of heat possible for a building containing tonnages of steel machines and automobiles. Do research thermal lag. It's one big drawback. One thing that the engineer obsessor other half researched to death was that the floor covering materials and home layout will determine the loop spacing, length, and how many zones you will need. A system designed for wood will need to have a different temperature than one for concrete or tile, which are more efficient at radiating the heat. There isn't a one size fits all solution. But be SURE that your system designer and your engineered wood floor manufacturer are in synch with the requirements.
    ...See More

    Radiant heat tiled concrete slab - to polished concrete slab. Possible

    Q

    Comments (5)
    Thanks...I try. Too many people *think* a concrete floor is a money SAVING project. It is not. A SLAB floor is money saving. It is ugly, unfinished and can be very rough on the feet. A properly finished concrete floor is beautiful but very expensive. Most people think slab concrete is the FINISHED floor and therefore cheap. What they do NOT appreciate is how UGLY it is and how much it stains and etches and degrades over time (chalky dust on the surface all the time). They are very disappointed in a SLAB floor. When they are told the cost to fix a concrete slab floor they look at the refinisher like they have 2 heads and say, "Well if it's going to cost me $10/sf why don't I get hardwood and be done with it?"
    ...See More
  • GreenDesigns
    5 years ago

    Vinyl isnt rated go over radiant.

  • weedmeister
    5 years ago

    When did radiant become efficient?

  • Elmer J Fudd
    5 years ago
    last modified: 5 years ago

    " Except on the coldest days of the year, the floor should be at room temperature "

    Oh my, this fellow doesn't seem to understand radiant heat either.

    "Heat" flows from warm to cold, that's what radiant heating is. If the floor is the same temperature as the air, it's not "radiating" any heat. The floor needs to be quite a bit warmer than the air to warm the room.

    For reference, maybe you've experienced buildings with radiators. They're warm to hot when giving off heat, especially hot if an old fashioned steam system. The fluid in a radiant floor doesn't get nearly as hot as for a steam radiator but it heats the same way. Compared to a radiator, the water is not as hot but the radiating surface is much larger.

    In most areas, the most efficient and cost effective way to heat water for a radiant system is with a natural gas boiler.

  • PRO
    Springtime Builders
    5 years ago
    last modified: 5 years ago

    Forgot a point about using decorative concrete professionals. I think using the concrete as the finish is the most energy efficient option while also being a great looking and durable floor. Someone just started a thread about [concrete finishes over radiant slabs.[(https://www.houzz.com/discussions/radiant-floor-how-to-choose-a-product-to-seal-a-concrete-for-a-house-dsvw-vd~5619767?n=17) While it's possible to get wood-look stamped concrete, I think the best concrete finishes minimize texture and joints. Less work to grout and clean.

    Weedmiest, I think radiant has always been considered efficient. Engineers tend to love them because water carries heat more effectively than air. With good designs, there is little waste but it's the cost effectiveness that's always been in doubt for climates with cooling needs. Ductless heat pumps are the new darlings of efficiency and cost effectiveness.

    As for comfort and temperature, near room temperature would have been better description for radiant floors, the point being you probably shouldn't feel any warmth to the touch with an efficient building envelope. A radiant floor close to the temperature of a radiator might represent a home with all the windows open.

    Cost-effectiveness depends on utility rates. Ground source heat pumps (water-to-water) can beat NG in most markets for radiant but are expensive upfront, maybe not a problem if the budget includes heat pumps for Air-Conditioning AND radiant floor mechanical systems.

    Air-to-water heat pumps for radiant and hydronic systems are growing in popularity and while it takes a savvy team to implement them, they too can beat NG in most markets for efficiency and simple fuel costs. They are much cheaper than ground source but probably more expensive than NG boiler considering appliance-only upfront costs.

    In markets where NG still beats heat pumps in simple energy costs, its smart for new construction to include the costs of the additional gas infrastructure. Both new and existing comparisons should account for minimum, monthly gas fees. For homes mainly considering it for heating, the 2015 nationwide average of $11.25 per month adds $2700 over a 20 year life appliance with no inflation. For homes considering gas for ANY needs, indoor combustion adds risks to indoor air quality and the future of homes is all-electric.

  • deziree_worster
    Original Author
    5 years ago
    springtime builders - do you have any opinion on solid core vinyl planks as an alternative to tile over radiant?
  • live_wire_oak
    5 years ago
    last modified: 5 years ago

    Vinyl has temperature limitations that do not work with radiant heat. Unless you like a bunch of warpage and nasty looking gaps. Wood has limitations as well.

    If you want radiant, tile is your friend. It becomes part of the thermal mass. It doesn't have insulating properties that fight against the thermal transfer.

  • PRO
    Oak & Broad
    5 years ago

    Dont forget the option for high quality Wood floor thats rated for radiant heat!

    Educational Plank Flooring Examples · More Info


  • PRO
    Springtime Builders
    5 years ago

    Green designs and live wire oak are probably right, might be tough finding willing manufacturer but I think this has a lot to do with traditional systems serving inefficient building envelopes. An efficient house is not going to have radiant floor temperatures too much higher than typical room temperatures. Certainly less than floors exposed to south facing windows. I would reach out to some high end LVF tech reps.

  • Elmer J Fudd
    5 years ago

    "An efficient house is not going to have radiant floor temperatures too much higher than typical room temperatures. "

    Repeating erroneous comments doesn't make them any less erroneous.

    If a radiant floor is the same temperature as the air, it will give off no heat. If it's 10 degrees warmer than the air, it will give off almost no heat. Call it no heat.

    Just for the sake of argument, how are you going to get a boiler or a heat exchanger from a heat pump to limit the water temperature in the radiant system to, let's say, 75 degrees. Right, can't be done. Start in the low 100s for the real answer.


  • PRO
    Springtime Builders
    5 years ago

    Don't confuse water temperatures from appliance with the floor temperature. From Inspectapedia on radiant floors: "Typical radiant floor systems operate at 85 - 125 °F water temperature entering the tubing, and put the floor surface temperature about 5 degrees above the room thermostat set temperature."


    That's presumably assuming existing, leaky and inefficient construction, probably applying to most people's experiences with "warm feeling" floors. A new home that is blower door verified and has current prescriptive insulation minimums will have lower floor temps on average.


    A passive house level home might have radiant floor temps ~1 degree difference in thermostat setting but that's a guess. It's at passive house levels or maybe even weaker that a radiant floor system hooked up to electric resistance heating source might be more cost effective than NG, using an electric utility demand control rate system. Though not yet common, our utility has begun offering this and expect many more to follow. Depending on utility rates, such a set up might put electric resistance floor heating lower than NG for average level envelope efficiency.

  • Elmer J Fudd
    5 years ago
    last modified: 5 years ago

    Your knowledge seems to stem only from internet searches. That's not knowledge or know-how for most people's perspective. This comment (from a house inspector site no less) is laughable. If water is leaving the boiler at 125 degrees, how does it lose 50 degrees by the time it reaches the underfloor tubing?

    Keep your posts coming, I'll call out your (or anyone else's) obvious misinformation when I see it. I'm getting close and I'd rather see comments not so unfounded.


  • PRO
    Springtime Builders
    5 years ago
    last modified: 5 years ago

    My knowledge comes mainly from college education in construction science and technology with over 20 years of construction experience in supervisory roles. It's nice to include reliable sources for credibility and further learning for readers.

    Don't confuse temperature of underfloor tubing with surface temperature of floor. Tubing runs can be long and 125 sounds like too high of an appliance exit temp for an efficient home. From a well respected GBA source All about radiant floors who is quoting another popular radiant floor article:

    ""Wilson described this problem in his 2002 article. “Heat is transferred from an exposed slab to the [indoor] space at a rate of about 2 Btu/ft2•hr•°F,” Wilson wrote. “In a well-insulated house, this rate of heat flow means that even when it is very cold outside, the slab can only be a few degrees warmer than the rest of the room or the room will keep heating up. For a concrete slab to feel warm, however, it needs to be about 80°F. Thus, for most of the heating season, the greatest feature of radiant-floor heat — a warm floor — won’t occur.”

    In many well-insulated homes, a “radiant” floor may be maintained at only 75°F — which is less than the temperature of your bare feet."

  • Elmer J Fudd
    5 years ago
    last modified: 5 years ago

    You read (and respond) selectively.

    I didn't say the floor would be HOT. I said he had to be warmer than the air to give off heat. You said it would be the same temperature. Twice. Which is wrong.

    80 degrees to maintain a temp in the high 60s may often be about right. To raise the indoor temp, a much higher floor temp would be needed or many, many hours.

    Yes, I know that feet are 98.6 degrees.

  • PRO
    Springtime Builders
    5 years ago
    last modified: 5 years ago

    A 98 degree temperature would feel hot on feet. An 80 degree temperature might feel warm. A surface temperature at or near thermostat set point will feel no different than all the other surfaces in the room. The point for efficient construction is that choosing radiant floors for feelings of warm feet will lead to disappointment and possibly discomfort. If it's high enough to feel the heat on feet, it will be an uncomfortably hot room temperature.

  • Elmer J Fudd
    5 years ago

    More misunderstood reading and a non sequitur comment.

  • armoured
    5 years ago
    last modified: 5 years ago

    I'm not getting into this argument, but I have some radiant floors and nearby rooms that do not (same floor covering). And I can attest from personal experience that the difference in what feels 'warm' to stocking feet can be very noticeable from only small differences - feet (and other skin areas) are very sensitive to temperature differences when in direct contact.

    The feeling of how a slightly-warmer floor adds heat to feet compared to how a slightly-colder floor saps heat out of the body is very, very noticeable. A few degrees difference celsius is all it takes - for example, 22C (72F?) to 24C (75 or 76F?) can be a noticeable change from a floor that feels cold enough you want to have slippers or a rug, to one that feels nice and warming - not just neutral but pleasantly warm. You can feel the heat even if the room isn't unpleasantly warm.

    (Note I am saying 'can' be enough - I'm sure ambient temperature, flooring material, other factors can change the perception).

    I have one section of radiant floor in a different part of the house that always feels too warm (but not hot) to me - and the temperature of the floors there is I think about 26C. This is the only room in which the 'feel' of radiant heat from the floor is noticeable separate from the direct contact temperature (i.e. you can feel the radiant heat even without touching the floor, like on face or arms).

    Or perhaps I'm getting older and more sensitive; cold car seats now always feel uncomfortable, and the heated seat a huge difference.

  • David Cary
    5 years ago
    last modified: 5 years ago

    In a tight house that loses very little heat, the radiant floor doesn't get that warm. In a leaky house, the floor needs to get warm. It is a well described phenomenon. Floors that are warmed on purpose and are only in part of the house are different.

    Either way, a floor that is warmed to 75 isn't going to be a huge problem when it comes to the material on top, while one that goes to 90 is more likely to have issues.

    So there are experiences with radiant floors with a 1980s house and there are experiences with radiant floors with a tight 2010's house. Since OP is focused on efficiency, their house will likely be tight. The floor will be warmer than air temp but not by much.

    Comparing 200 sqft of a radiator (the floor) in a tight house to a 8 sqft radiator in a loose house is going to show lots of differences. But just for some math.

    Room temp 70. Radiator temp 120. The surface area of the floor is 25 times greater in my completely made up example. A floor temp of 72 would heat the room the same as a radiator at 120. Does anyone think a floor temp of 72 is going to warp anything? Now reduce heat loss by 75% - which is typical for modern construction compared to average house and 70.5 degrees would warm the tight house as much as the 120 radiator in an old house. The thermal mass of the floor is probably more important and is more than 25 times greater than a radiator. A square foot of slab at 4 inches thick is about 50 pounds so here we are at 10,000 pounds in my 200 sqft room. The first radiator I found was 35 pounds. So about 300 times greater.

    Now - the boiler will overshoot and you are going to see higher temps but you should not see 80 or anywhere close to that. Of course the water leaving the boiler is higher than 80 but it is being dispersed in a huge thermal mass.

    A tight house changes things quite a bit. I haven't turned the heat on in our master bedroom even when it got to 15 degrees outside. Our 2 bodies keep the room warm. We have a conditioned attic above, 2x6 walls with netted fiberglass, advanced framing, and R-3 of foam on top of framing, sub slab insulation and thick floor to ceiling curtains. I turn down the house (separate system from the bedroom) to 65 and our bedroom is never below 64.

    In a really tight house, radiant floors do not add some amazing comfort. Anecdotal experiences compared to uninsulated floors will absolutely show a difference. Insulating the floor (and tightening the house in general) is a lot cheaper than radiant floors.

  • deziree_worster
    Original Author
    5 years ago
    what flooring do you have??
  • deziree_worster
    Original Author
    5 years ago
    our house has above code insulation and well insulated slab - my main question is whether I am silly for not doing tile throughout the house to be able to have that added thermal Mass? my alternate choice is luxury vinyl planking with a solid core, which is radiant rated, and also has a lifetime warranty. cost is very comparable to tiling. effort, labor, on the other hand, is much higher with tile. this is why I'm considering luxury vinyl.
  • deziree_worster
    Original Author
    5 years ago
    can you all answer with this in mind?
  • just_janni
    5 years ago

    I would think that the LVP won't conduct the heat as effectively as the tile, and therefore you will decrease your efficiency. The almost monolithic bond between the tile and the floor is a very good conductor (likely only second to just a concrete floor alone) and then the LVP isn't as conductive to the heat AND the bonding to the floor is not as consistent. It's a compromise - and - IMO really takes away from the idea of radiant - but not an expert on LVP by any means.

    Also - David is right - in a tight house - the floor won't be all that warm to the touch. If a 4" slab has be heated to 85 or 90 degrees, you should probably be focused on other areas for improvement and efficiency vs radiant slab.... we are forgoing radiant heat because our slab is so isolated from the ground, and once it gets to temperature, it's a giant energy storage facility anyway. We'll use it passively - with sunlight warming it in the winter and then it can radiate heat back during the night. The slab is so large - it simply doesn't have to get that much of a differential in order to be effective.

  • PRO
    Austin Air Companie
    5 years ago

    I have been considering the same for a home I am renovating, but I am not planning a heated floor, I've decided this would be too much fuss for my climate. (Katy, Texas far west suburb of Houston)

    With that said, I think tile is the colder alternative to luxury vinyl planking. So if you get the tile with a heat source, due to the better thermal transfer I think the tile would be the better choice just for that reason.

    The tile is probably at best a 30-60 year decision, provided the floor is prepped / leveled etc. that tile (ceramic or porcelain) will last a life time.

    The luxury vinyl planking could last a long time as well, I think the biggest concern with that choice would be warping and possibly loss of color or bleaching due to sunlight hitting it (at least for my climate). It's quite indestructible as I took a couple of free samples from HD trying to scratch them, while that is possible it's quite easy to buff that out to the point that you really can't tell any damage was done.

    A far cry from laminate flooring, I can tell you that much. Cost wise both are pretty much the same... You will still have to prep the floor, probably much more so with the luxury vinyl plank because other wise it will probably warp. So I think the tile choice would be a little more forgiving as you can adjust the mortar bed on the fly while laying the tile.

  • PRO
    Springtime Builders
    5 years ago

    I'm sticking by my first post but it would be telling if you could provide the R-value under slab. What type of insulation at how many inches? If you are R10 or higher, under and at edge of slab, then it would be hard to measure any difference in energy efficiency. If really concerned about it add more sub slab R-value. Tile is better on paper, but I don't think you could measure much difference in the field above R10.


    Please tell us what brand LVF is approved for radiant so it helps us and other readers finding this thread in the future. As David and Janni concurred about temperatures, I suspect most LVF is going to be fine in an efficient home with relatively low floor surface temps, even if it's not listed or rated for radiant.

  • SJ McCarthy
    5 years ago

    I know of some Korean made LVT/LVP that is rated for in-floor radiant heat:


    EZ Lay and Drop & Done. They are vinyl products that must meet the demands of the Korean market....which has a HIGH rate of in-floor heating. If you must go vinyl then work with product that allows 125F as it's top range. The EZ Lay and Drop N Done will both get you there. There are VERY FEW vinyls that will give you this option. Very, very, very, very few. I mean almost none. So few in fact you will rip your hair out looking for them.


    And there are some vinyl products that use the wording "heat resistant" only to have a caveat in the warranty area stating 85F is the maximum....which is the NORMAL maximum for NORMAL vinyl! Wow. Talk about misleading!


    Anyhooo...you will need a vinyl product that has maximum ratings of 125F (52 C). The cost will be around $4-$7/sf depending on your market and ease of availability for the EZ Lay and Drop N Done.

  • deziree_worster
    Original Author
    5 years ago
    we have r 15 sub slab insulation
  • deziree_worster
    Original Author
    5 years ago
    going with lumber liquidators solid core tranquility ultra line.
  • SJ McCarthy
    5 years ago

    Uh-oh. You may not want to do that. If you check the installation/warranty instructions you will notice the floor has LIMITED heat exposure ratings. It is even LESS than traditional LVP. Remember I mentioned 85F as being the highest most LVPs are rated for? Well this one has a LOWER rating....not higher. It is allowed a maximum heat exposure of 80F. If you don't believe me, go ahead and look at the link below and check under "Radiant Heat".


    http://www.lumberliquidators.ca/assets/images/installation/AA-LVP-002_06.pdf


    This floor is NOT allowed to sit at temperatures HIGHER than 80 F. Oh dear. Not good. I wouldn't put this in front of a sliding glass door let alone over top of hydronic heat! And that is WITH the glue down method....which is more expensive.


    Please please please check the installation link I've listed! LL has made the statement that it is rated for hydronic heat....but then on the installation instructions they "revoke" that rating by using insanely low heat temperature allowances.


    Please do not use this product. It is not what you think it is. It must be kept between 60F and 80F. Nothing lower and nothing higher. Even for LVP that is a poor rating.


    Go with the high end stuff out of Korea. Not the low-grade stuff from LL. Their wording is "just hype". They give you hope in on the front of the page only to take it away with the fine print. And at $3.20/sf, this could be a very costly mistake.


    $3.20/sf x 2400sf = $7680

    Add in $1/sf for the glue = $2400

    Add in $3/sf for install = $7200 (glue down costs more money to install)


    That is a lot of money to spend on something that is not specifically designed to work with in-floor radiant heat.



  • deziree_worster
    Original Author
    5 years ago
    does it make any difference if I am in a cold climate? for instance, in the Maine summer with it it's only really warm maybe a month maybe two months out of the year, we would not have are slab heated there for the slab would be cool, possibly combating the weren't coming through the windows, which we could also use shades to help with in the summer. in the winter, we get very cold
  • deziree_worster
    Original Author
    5 years ago
    I would rather install tile then spend $7 a square foot on vinyl.
  • GreenDesigns
    5 years ago
    last modified: 5 years ago

    Lumber Liquidators complete junk doesn't belong with a 30K home HVAC upgrade. Plastic floors in an upscale house isn't ever going to fly. Or is it the radiant heat that doesn't belong in that entry level of a house? One of those things is not like the other. If you want AC, you're throwing money away with radiant. Plus there's the problem of humidity control, which is required in modern buildings. It just got a lot more expensive and problematic to do without ductwork.

  • SJ McCarthy
    5 years ago

    It's the infloor radiant heat that will ruin the low-level vinyl. To get the room "up to temperature" you have to set MAXIMUM heat out put (measured at the level of the floor...not room temp) to be 75 F. That means your air/room temp will NEVER get more than 70 F. Ever. Which means in a cold climate, you may never feel comfortable. And on really cold nights, your home could drop to 65 F because the thermal mass takes ++ time to react AND it is preprogrammed NOT to go above 75 F in the slab itself.


    All of these restrictions would be in place because you decided to go with an inferior vinyl product that is not recommended for 'heat' of any sort. Despite what the advertisement says, it isn't good enough to be used with a whole home in-floor heating system. It is only good enough for a secondary in-floor heating system that is designed to take the chill off the feet...the rest of the heat would come from the furnace/duct system.


    If you want cheap, then go for carpet. If you want an efficient floor that will work for 20+ years then go for tile. If you want a vinyl product then pay the price and work with the right type of vinyl that is rated for 53 C (125 F).


    Heck...even a $3/sf laminate would be a better choice than a low-level vinyl. The LL stuff is really a lower quality product than even Home Depot or Lowe's.

  • David Cary
    5 years ago

    If the walls and insulation is good, a 75 degree floor will keep the house comfortable - even in Maine. There is absolutely no way that you need or would ever want an 125 degree floor.


    I am not saying that I would buy something from LL though.


    Also in Maine, a/c is probably not required. Also a DIY pex radiant in slab is pretty inexpensive.

  • PRO
    Springtime Builders
    5 years ago
    last modified: 5 years ago

    I agree. At startup or bringing a cold room quickly up to temperature could see temps over 85 so a regulator might be in order. The bigger concern to me would be floors exposed to sunlight. Appreciate SJ McCarthy bringing this issue up. Seems like an easy way for cheap floors to squirm out of warranty.

    In case others missed it, the inspectapedia link suggested that 85' is a maximum recommended temperature for radiant floor surface temp which is assuming existing, inefficient construction.

  • Elmer J Fudd
    5 years ago
    last modified: 5 years ago

    In case others missed it, home inspectors are anything BUT HVAC experts. They don't install systems nor repair nor maintain them. The linked source shouldn't be considered authoritative though it may be seen as such by someone knowing little about the subject.

    If you really want to know about operating temperatures, talk to an HVAC contractor who installs and maintains such systems. General contractors, at least in my area, are notoriously clueless about HVAC matters.

  • armoured
    5 years ago

    A question on this: is it reasonable to say that radiant floor heat may help in efficiency as works well with condensing gas boilers and heat pumps (each of which have specific issues with return temperatures and/or optimal heat output/lift temperatures)? I believe I have read points to this effect but would like to confirm.

  • David Cary
    5 years ago

    Radiant floors help with efficiency because water is easier to move around than air. Ductwork in forced air units can leak (will leak) and if that leak is out of conditioned space, that hurts efficiency. Also moving air around can create negative pressure in a certain room (or the whole house if it leaks out of conditioned space) and that can increase infiltration. Infiltration is outside air getting in which is not conditioned. This is a significant contributor to heat load in an older house - and still an issue with newer houses.


    Forced air furnaces and heat pumps are efficient. Heating water isn't significantly better - it is just less subject to the above distributional issues.


    In response to Elmer - I haven't really found an HVAC contractor who has a great understanding of all HVAC matters. I mean how many terrible installations have your seen? Do we trust any of them to do a zoned system properly? Sorry to paint such a broad brush, but my experience hasn't been great. Time to go block off a few ducts to internal hallways/bathroom that don't need conditioning.... (static pressure on supply is .15 and I will check it after blocking the ducts).

  • PRO
    Springtime Builders
    5 years ago
    last modified: 5 years ago

    It's good to question home inspectors but that source is not from some random. They train and educate the home inspection industry. Their advice is generally sound and easy to understand.

    85 is not pulled from thin air. It's an established maximum recommended temperature for radiant floors as pointed to by Jon Siegenthaler a PE who trains other engineers and installers on radiant floor heating systems.

    I certainly wouldn't trust most HVAC contractors to properly calculate new, efficient construction heating and cooling loads. That is best left to a third party mechanical engineer or HERS rater specialized in that type of work. Of course I don't trust most builders to meet international code minimums nor most architects to specify the appropriate details to get there either.

    Surely there are homes that need floor surface higher than 85 to meet thermostat settings, but those are very lousy homes whose low fruit would probably include blower door directed air sealing and added roof insulation.

    If people are still considering radiant floors and skipped my earlier links, All about radiant floors is required reading for those building new. It's possible that radiant floors could be less efficient than forced air. Inefficient circulator pumps that run 24-7 or inadequate levels of sub-slab insulation could be recipe for more energy use than forced air heat pumps. Earlier I mentioned R10 as enough subslab insulation but that was my southern bias and may be inaccurate depending on climate. Reading back it looks like R20 or above might be more appropriate for cold climates. All that sub slab insulation doesn't help the case for cost-effective space conditioning with radiant floors.

  • Elmer J Fudd
    5 years ago
    last modified: 5 years ago

    " 85 is not pulled from thin air. It's an established maximum recommended temperature for radiant floors as pointed to by Jon Siegenthaler a PE who trains other engineers and installers on radiant floor heating systems. "

    You need to read more than the first two sentences of the article you linked to. Had you read (and understood) the whole thing, you'd see that that number is only for " situations of prolonged foot contact with the floor ". Presumably that means barefoot contact.

    Also, later in the article that you apparently missed are measurements for temperature of floors with water temperatures in the 100-120 degree range, and the resulting floor temperature as affected by the spacing of the tubes.

    Please read more carefully and know what you're talking about, you'd reduce the amount of misunderstandings and misinformation you often have in your comments.

    By the way, you seem to have abandoned an earlier argument you made that water in radiant subfloor systems is only at room temperature. More Google searching gave you that understanding?

  • Elmer J Fudd
    5 years ago
    last modified: 5 years ago

    David Cary, you're right in a sense. The skills to be a good capable mechanical (HVAC) contractor are an odd mix of mechanical/technical (as regards the equipment itself) and old-fashioned craftsmanship, doing duct and load calculations, fabrication of parts from scratch (the sheet metal work), and the normal challenges of building when problems need solving. Then measuring the results and tweaking.

    Of the last three HVAC contractors I've worked with (for substantive work, not repairs) two have been outstanding.

    I understand that radiant heating is a completely different animal and people wanting those or having those are best served finding a contractor who specializes in them. Even in my mild weather area, such contractors exist. (I have a friend whose house has in-floor radiant heating and there's a local contractor who works on nothing but those systems).

  • PRO
    Springtime Builders
    5 years ago
    last modified: 5 years ago

    Glad we now agree that 85 is an established threshold that radiant floor designers use as a recommended maximum for floor surface temperature. Foot contact with the floor makes the second way high temperatures lead to discomfort. 85 is evidently too hot for those expecting warm feet and will definitely lead to uncomfortably hot room temperatures, in efficient homes.

    There still seems to be confusion regarding water temperature and floor surface temperature. The temperature of the floor surface will be lower than the water temperature in the tubing. The water temperature entering the tubing loop from heating appliance, will be warmer than the temperature exiting loop, on its way back to the appliance to be reheated.

    The only mention I made of water temperature was that 125 seemed too high for an efficient home. Perhaps not for a long tubing run with short spacing but I still think it seems high and engineers generally don't like long tubing runs. I've personally installed tubing on a spec of mine and for other builder friends. We installed short runs with wide spacing for better zoning and they were for efficient envelopes. Few ended up being hooked up to an actual appliance. Why spend that money when the required AC can handle the heating too.

    The "at" which I corrected to "near" room temperature comments were in regards to floor surface temperature, which is a widely accepted fact for those involved in efficient construction. From All About Radiant Floors:

    "Why isn’t my floor warm? Homeowners who look forward to walking barefoot over warm floors are often disappointed by homes with in-floor hydronic heating. That’s because these floors are rarely as warm as most homeowners expect."

    From that article's case study (keep in mind difference of water temperature and floor surface):

    “On the design heating day [the coldest day of the year], the water flowing through the tubes in the floor will only be at 85 degrees,” said Robb Aldrich, an engineer at Steven Winter Associates"

    From energy expert Alex Wilson's article describing a level of home performance between passive house and international code minimum:

    "in a highly insulated house (and I’m talking about a really tight house with at least R-40 walls, an R-50 ceiling, and triple-glazed low-e windows), such a tiny amount of supplemental heat is needed that a radiant floor needs to be kept no more than a few degrees above the air temperature—or else overheating will occur. If a concrete-slab or tile floor surface is maintained at 72 or 75 degrees, it will likely feel cool underfoot—since it’s at a lower temperature than your feet. So you may not get that delightful benefit of a warm floor surface.

  • Elmer J Fudd
    5 years ago

    "Glad we now agree that 85 is an established threshold that radiant floor designers use as a recommended maximum for floor surface temperature. "

    Nope, that's not what the article said.

  • PRO
    Springtime Builders
    5 years ago

    Yeah pretty much did. Here's another source that concurs..

  • Elmer J Fudd
    5 years ago

    You didn't read that one very well either.

    I've worked with a lot of contractors, including generals and including one medium sized project recently, and all impressed me with their knowledge and know-how. All knew what they knew because they knew it and they knew it on the spot and when asked. None needed to do Google searches to find information nor did they ever seem to confuse or misunderstand the learning they had. You somehow don't convey these same abilities.

  • dan1888
    5 years ago
    last modified: 5 years ago

    It's a developed skill to be able to convince someone who doesn't have experience or knowledge of a subject that what you're telling them is true without any supporting information.

    I've never been the type to find those people very persuasive when dealing with technical building questions. I like those facts to come from multiple reviewed sources with logical explanations I can understand and hopefully learn for myself from. And I'm capable and willing to put the effort in. I found the articles a good source to further build on.

    The article stated you may come across an individual who just wants hydroponic floors without regard to the comparative efficiency or cost. As an engineer you can design the house to lose heat at a rate fast enough to allow the floors to need to be heated to a comfortable barefoot temperature to replace the heat loss. The added heating cost gets the owner a comfort benefit he's willing to pay extra for. Similar to the added heating cost he may be willing to incur for large windows facing a view.

  • David Cary
    5 years ago

    An engineer may not be able to design a house to lose heat fast enough if codes won't let him. Surely the OP isn't trying to do that anyway.

    The concept surprised me when I learned about it a decade ago - that a tight house will not have particularly warm floors with radiant heat. Radiant floor heat is a comfort thing that isn't as comfortable as a tight house. Strange but true.

    That being said, a warm floor feels very nice to bare feet.


  • deziree_worster
    Original Author
    5 years ago
    well, these would have been great considerations BEFORE installing 2400 SF of radiant. Now I'm feeling uneasy, unsure... but there is absolutely nothing I can do at this point. Hopefully, it will be cost efficient and warm enough and hopefully, my floors are ok.
  • Elmer J Fudd
    5 years ago

    deziree, get a flooring material that's rated for underfloor heating and you should be fine. Have the system set up and debugged by an HVAC contractor who knows what he or she is doing with radiant underfloor heating. The comments in this thread show that general contractors don't often fit that description.