Engineered wood is supposed to be much more stable than plain wood. Should this even be a worry? Note that quarter sawn wood is best to resist temperature and humidity changes. In addition, my resources indicate that hickory is in the middle of the wood flooring selections, not especially sensitive. Temperature rise to 80%? You mean 80 degrees?

You should think carefully about opening the windows at night if you are doing it to save energy. If you make the house humid, the system has to use a lot of electricity to wring that water out of the air. Think about a pot boiling on the stove evaporating the water. The same amount of heat must be sucked out of the water vapor in the air and all the water that becomes ensconced in the materials in your home. In addition to that, at night with a temperature drop outside, the system does not have to use much electricity to maintain temperature or dehumidify. Calculations should be able to show if it is worth opening windows.

Stop believing that furnaces dry air more than hydronic coils or any other heat emitter. What drys air in the wintertime is air exchange with the outdoors. If you have a well-sealed home (perhaps with an energy recovery air exchanger) you will retain humidity inside. Add the humidifier later if you need one. but keep in mind that some types require a lot of care to keep mold at bay. The only thing a forced air system might do to influence humidity that radiant floor or radiators don't is add to air exchange problems. If the ducts are outside of the home envelope (attic or open crawl space) and they leak, you suck air in from leaky returns and blow it out from leaky supplies. Then make up air rushes in or out from cracks and other leaks. This can. of course, result from unbalanced return air inducing pressure differentials between rooms.

Depends where you live in Sacramento. If you're in the "Delta Breeze" area then, yes, you'll have that humidity coming off the delta, year round. If you're further south (Elk Grove/Galt/Stockton) then you have heat, heat, dry heat! I always thought of the region as pretty stable, humidity wise, compared to, say the East and South.

ionized_gw, thanks for your input.

I have read that Hickory can pull off the engineered base to to differential water absorption between the veneer and the backing, however I don't know what humidity levels are necessary to create this problem.

As to opening the windows, I believe in our case it is OK, although I haven't run the calculations. I know in somewhere more humid in the cooling season, it is more efficient to leave them closed for the reasons you said. Our summer humidity isn't crazy - 45% more or less.

I've never had an air sealing test done at this house, but when we got he HVAC system, ducting and attic insulation replaced a couple of years ago by a whole home performance contractor, they did air seal the attic. I'd asked about air sealing the crawlspace and he'd said that the vast majority of the loss is through the "high holes" so while he could also seal the crawlspace ones, he didn't think it was worth it. I'm assuming that we don't have leaking ducts since they were replaced 2 years ago- I certainly hope so! However, we don't have an energy recovery air exchanger.

Oh, and I did mean 80 degrees, not 80%! Thank you.

sktn77a, so did I! I was pretty shocked by the relative humidity variation I was getting on the web.

Maybe for hardwood, the Relative Humidity doesn't matter- just the total moisture in the air?

We live in downtown Sacramento, so yes, I believe, we live in the Delta Breeze belt.

It would mean putting off the flooring project, but you could get some flooring samples and do your own testing under real conditions. You could to some more extreme testing as well by setting up your own humidity or drying chambers.

Hickory is not stable enough for hydronic is underfloor heating. But that’s OK, because you don’t live in a location that is remotely suited to using radiant heated floors. You’d need real actual sustained cold, with no yo yo’ing of up and down temperatures. The lag time on radiant is far to great to deal with large rapid temperature swings. And the payback period is decades even for those who do live in areas where it is appropriate.

Put down your hickory engineered. And do a different type of HVAC.

Sophie Wheeler, we have hydronic heater in the attic that heats the air that the blower forfor our forced air system- it is not underfloor heating. I'd though that the hydronic system didn't dry out the air as much as a furnace does, but from what ionized-gw says, it sounds like I'm wrong.

Do you know if the wear layer thickness will affect the stability?

Hydronic usually refers to hot water radiant/baseboard systems. So you have a boiler that provides heat for a regular forced air system?

Yes, there's a common myth about heatpump/hydronic/gas/forced air/baseboard systems having differing humidity characteristics - they don't.

Thanks, sktn77a. Good to hear (from 2 people!) that the heating system doesn't effect humidity in the house differently.

Also, I didn't know that hydronic usually refers to a radiant / baseboard system- thanks for informing me. Out of curiosity, is the boiler that you guys refer to the same things as a regular water heater that also supplies the hot water for our shower, dishwasher, etc? Because that is what supplies the hot water for my hydronic heating system.

To be sure heat affects humidity, but only because RH decreases as temp increases give that the absolute humidity is constant. The only caveat is that forced air with leaky ducts increases outdoor air exchange.

Hydronic heat includes a boiler on one end, and on the other end, heat emitters include radiators, convectors, radiant floors (and sometimes ceilings or walls), and your hydrocoil in an air handler. Those water uses that you listed are summarized by domestic hot water (DHW).

DHW is generally separated from the hydronic heat water. The hydronic heat loop is a closed system and if fresh water is constantly brought in, special precautions need to be taken to prevent corrosion -- stainless steel pumps and much more. It is generally thought of as a bad idea, even then, due to potential stagnant water issues. It may be counter to plumbing code. The same boiler/water heater can be used to heat water for both purposes, but a heat exchanger of some sort is used. This is most often what is called an "indirect tank" (including the heat exchanger inside) that heats and stores DHW using hot water from the boiler to heat that water via the heat exchanger. It could be just another loop in your system like the one that runs to your hydrocoil. There are other ways to split the boiler output for potable, DHW and heat. I'd be surprised to find that your DHW and heating water are intimately connected.

Low mass combination boilers are becoming more common providing hot water in a way similar to the so-called endless, instant, tankless,.... for both the domestic hot water and heating loops. They have either two primary heat exchangers for the two systems or a water-water heat exchanger like the indirect tanks.

Super interesting, ionized_gw. Now I'm curious about my system. I'd assumed it was all the same water, but maybe not.

Just for fun, I suggest you shut up the windows for a full 2-3 weeks, run the dehumidifier/humidistat for those weeks and see (ahem...write down the numbers from 3 points in the day) how much fluctuation you get. Then go ahead and do what you NORMALLY do (open windows, run AC with higher temps) and then compare the numbers from the previous study.

Now you will have a full picture as to what *needs to happen with ANY wood floor based material (engineered, solid, laminate, cork, etc).

The HUMIDITY is the biggest issue. Engineered likes a window of 15%. BIG fluctuations are KILLERS.

Ex: 45%-60%

or: 35%-50%

You do NOT want swings BIGGER than this. Ever. So go ahead and do a 6 week "test". Three weeks with windows closed, AC on, humidity control up and running. Record three set times during the day. Now run the same 3 week experiment but as you "normally" live. After 6 weeks you will find out how you "life style" numbers compare to the "perfect" numbers. Remember: 15% swing is the BIGGEST swing allowed...and certainly not in one day. That 15% swing is from WINTER to SUMMER (over 4-6 months).

Good luck. Tell us how your experiment went.

"that’s OK, because you don’t live in a location that is remotely suited to using radiant heated floors."

Good LORD there is some awful misinformation on these forums!

If you asked an expert on the history of US residential home construction about areas of the country known for radiant floor heating, they would probably answer 1) the Levittowns of the northeast and 2) Eichler homes in Northern California. In fact, there are SO many of those system still in use, there's a contractor in the Bay Area who specializes in repairing them, including fixing buried pipe! Probably one of the only contractors of that specialization in the USA. Northern California is consistently chilly enough in winter that buildings certainly do need heat, and radiant floor heat works superbly in that climate!

But that apparently isn't what the OP was asking about anyhow.

My house had a very well engineered radiant floor system. Not aware of any leaks but was afraid about a decade ago to replace the boiler so went with heat pump/propane backup and 'scorched air'. Regret it, wish I'd hunted down a plumber who seemed like he could handle the boiler replacement, but the only good, honest local one I knew about (he was hydronic certified btw), told me he was wary about working on such an old system. He was trying to be a good guy: he didn't want me to spend thousands and then have the 60 year old system spring an unfixable leak. As to the question at hand: some previous owners had foolishly put in Pergo flooring in most of the house. Probably not optimal but it was holding up fine for the 4 years I did use the system. I think they might have a very slightly warped appearance compared to how they should look. The heat definitely "radiated" through the floors. And let me tell you, if you win the lottery and can build your dream house...go with radiant floor heating. It is the best. At least for parts of your house with appropriate flooring.

In doing my research, I found out about a system from the 1920s in the inner suburbs of Baltimore that was still working with no leaks. And that was a two story house with a second story of poured concrete floors!

Solid wood floors go back hundreds of years. What kind of dehumidifiers did they use one or two hundred years ago?

They didn’t have HVAC systems 200 years ago. Just fireplaces, or rudimentary gravity heaters in the basement with some very interesting ductwork. Slab on grade construction wasn’t around as a sstandard choice 200 years ago either.

And they put oakum, or rope, or sawdust and varnish, between the big cracks between the boards that resulted from the repeated edge crush action of the expanding and contracting.

I was first exposed to hydronic heat in 1963 as an intern when the homes were being constructed. Those same systems were failing in the 80’s with pinhole leaks. Copper encased in concrete doesn’t last forever. And lasts quite a bit less than forever in some places.

The use of tadiant in mild climates has very well known issues. Any heating system coupled to a large thermal mass is very slow to react to temperature changes. Etc.

SJ McCarthy, thank you for the advice. I'm not sure my dedication meets the requirements for the experiment! :)

However, I really appreciate your providing the amount of of humidity variation tolerable for wood floors of whatever stripe. I guess what we have going for us is much higher humidity during the heating season when the heating dries out the indoor air.

Sophie Wheeler, I'd never thought about homes 200 years ago simply accommodating huge cracks, but it only makes sense! Thank you for that perspective.

Also, it never occurred to me to mention that we are over a tall crawl space and have plywood (OSB? The flake type) subfloors. After I read your comment about on grade slabs, it finally occurred to me why people where assuming floor radiant system.

I'm grateful to you and all the other knowledgeable people who share their gained wisdom so freely.

Those same systems were failing in the
80’s with pinhole leaks. Copper encased in concrete doesn’t last
forever. And lasts quite a bit less than forever in some places.

As with anything, the better constructed systems lasted longer. Somewhere I saw a picture of one of the Levittown systems during construction. Very thin copper pipe was lain willy-nilly with irregular gaps. OTOH many of the Eichler systems are still working. In Europe, radiant floor heating with PEX is much more common than in the US.

The use of radiant in mild climates has very well known issues. Any
heating system coupled to a large thermal mass is very slow to react to
temperature changes. Etc.

Yes but by some people's estimations that would be a good thing. When a cold front came through in winter, the system didn't have to work overtime to keep the interior warm. I do remember on the rare case there was a warm winter day, the warmth of the slab would be more noticeable. But it never felt uncomfortable. (whereas a forced air system would maintain exactly the same interior temp. My carrier infinity actually has a settable degree of 'anticipation' based on outside temp, or whatever it's called.) There's a reason people who are familiar with them still spend big money to install and or repair such systems. In a mild climate like coastal California, the idea was probably that in the rare instance there a hot afternoon in winter made the interior too warm, you'd just open a couple doors to let cool air in. No big deal.

"Good LORD there is some awful misinformation on these forums!"

I agree. You're guilty of the same thing. Neither Eichler homes nor in-floor radiant heating are particularly prevalent or numerous in the Bay Area (where I live). Rare might be a better word for both. I know of one Eichler neighborhood in a very desirable town, Palo Alto, where Eichlers are often bought as knockdowns and replaced or significantly remodeled to have a more suitable structure.

Other houses built as tract developments or as custom houses rarely if ever have in-floor radiant heating in California. I know one person who has it, they're living in a house that was an experimental self-build project of an ambitious architect. They don't like it because the lack of ducts makes adding air conditioning a much more difficult matter, one they've decided to not do.

I have lived In some very old homes with wood floors in climes with damp summers and dried by central heat and many air leaks. I’ve never seen anything like the floor repairs that you describe, Sophie Wheeler. Can you provide some references that speak to the prevalence of that problem. I would love to see some pics as that might prompt better memory if I did see it and have forgotten.

Gaps.

Oakum

Sawdust and varnish.

Rope.

Cording.

Sophie Wheeler, Wow! So interesting!

Wow, I've never seen anything like that on the USA Northeast costal plain or anywhere else.....