Where is the house located?

Wow, no good answers.

Another option is a POU for vanity. A recirculating system that's motion activated and latches when you go in bathroom and turns off when the pipe is warm. Do it with a return line, not the cheezy way by using the cold water line. And a Hybrid Electric in the garage. It's the cheapest way to heat water. Propane sucks.

Do the math on the POU - you can approximate the amount of water in the PEX.

Make sure all hot water lines and recirculating lines are insulated to reduce wait time.

Here's the thing: You are going to use the master bath vanity often. Guest bath not so often.

The POU for the master vanity is the right idea.

If the recirc pump triggers when you walk in, you should get hot water pretty quickly without wasting water and without it running all the time.

Yes, the option to install a recirculating loop and pump is worth considering. Water gets recirculated back to the heater when it cools below a desired temperature. There are a number of different options to control the pump on/off time. With this option you're never waiting too long for hot water to arrive at a use point and it's not being wasted down the drain while you wait. Some models of condensing-type tankless hot water heaters have the pump and buffer tank built in so all you have to do is run the recirculating line. Your hot water line would need to be insulated by code so there's no change there.

If you have any other reasonable options to running water lines in an attic, they are preferable, in my view. If not, investigate a whole-house water shut-off like Moen's Flo valve.

Indeed some tankless water heaters do have recirculating systems.

They are in Texas - and have access to use the garage as a heat sink for a hybrid electric heater. And the alternative is propane... seems like a no-brainer to me.

If the alternative to running pipes through the attic is to run them through the slab, run them through the attic. The truth is that a leak in a pipe is going to do a lot of damage wherever it happens. Repairing drywall is so much easier than jackhammering the slab.

Don't put any plumbing outside, including water heaters. Just don't. Learn from the last incident. Don't compound the bad design issues of 100' hot water lines with an outdoor heater. It's a new friking house, not some hunting cabin in the woods that you are retrofitting with indoor plumbing!

I'm not a big fan of recirculating systems on timers. Unless you have a very predictable schedule I think it results in a lot of heat loss in the pipes. Typical pipe insulation has an R rating of 3. That's infinitely better than uninsulated pipes, but still a lot of heat loss over a lot of surface area (about 100' x 2 with the return line).

With a hybrid tank heater you don't have the initial delay of hot water that you have with the tankless. In this layout, with a tank heater, you would get hot water in the kitchen in a reasonable time without the recirculation pump being active. You only really need it to be active in the master bath.

Consider a recirc system but include remote control to turn the pump on and off as needed versus using a timer. With a new build it could be a wired control. I used X-10 stuff to turn ours on and off. I have timed how long it takes to get to the bathrooms. laundry and kitchen. There are more *reliable" systems for control but X-10 is the least expensive. Having to wait for x minutes for hot water to reach a given outlet is maybe a bit inconvenient but "what's time to a pig".

In addition to the time spent waiting for hot water to arrive, you should consider the quantity wasted down the drain and it's effect on your water/sewer bill. Our county is completely dependent on well water for potable water supply. It's an expensive resource and the price is indexed based on usage (the more you use, the more you pay per gallon.) Plus, you pay sewage charges on every gallon that goes down the drain so it adds up.

You could also put a hybrid hot water heater centrally in the attic. Sure it could rupture and create a bit of a mess but that could be planned for. We have something like that although a different floor plan. The kitchen is the furthest fixture with regular use so it has a POU.

Have you seen proprane prices lately?

2 tankless, at opposite ends, and forget the recirculating unless you like wasted money.

The cost of (2) condensing-type tankless hot water heaters is sobering and so is the installation cost. You'll need a gas line capable of delivering gas at the rate required by both heaters operating concurrently-- plus any other users in the home. I think you'd be better off to put a small electric hot water heater under the vanity to serve as a buffer tank. You can get a 6 gallon Rheem compact unit for less than $300. It plugs into a 120 VAC receptacle.

I'd vote for a standard electric tank at each end at ground level, possibly in a bumped out insulated exterior location, externally accessible. This would provide redundancy and easy repair/replacement. Further, a propane-fed motor-generator in the yard would provide back-up to the house and heat. This will limit propane heating of the hot water to only power failures requiring the generator. Modify architecture accordingly.

Trading away hot shower performance to save a little initial cost in a project covering thousands of square feet of house seems as misguided to me as Texas' mix of prime power resources.

We'd need to know the unit costs of each alternative energy source in order to make a recommendation based on economics.

Isn't it telling that the insurance companies don't charge more for hot water heaters in the attic? Do you think they are irrational? Don't you think they have run the numbers? They ask many questions and presumably decide the rates based on those questions.

What model being discussed has "traded away hot shower performance"?

From an energy accounting standpoint - and this should match financial over the long term - a heat pump hot water heater is the best in a southern area without NG. That is the situation it absolutely works the best for. Helps that most of the south has cheap electricity.

I have NG and still went with the heat pump.

@David Cary,

Best practices evolve from practices that weren't.

I live in a mixed-humid (coastal VA) climate. We occasionally get cold snaps that can last up to a week. It's not a coincidence that they typically occur when folks are enjoying some time on a tropical island far, far away. With nobody home, and no hot water being circulated, the lines to a hot water heater in the attic can freeze, burst, and cause a flood that goes unchecked until the neighbors see icicles forming where water is leaking from the home. Yes, really. It's happened in our area often enough that people should learn the lesson.

The risk isn't limited to hot water heaters in attics. One homeowner who was enjoying a tropical vacation learned that insulation by itself isn't sufficient to keep a water line to a humidifier from freezing. They had forgotten to open the valve in the fall to supply water to the humidifier. With no water flowing, the water in the lines eventually reached the attic temperature which was below freezing. The line burst and water flowed unchecked for days. It was a heck of a mess and a huge insurance claim.

We've built two homes in the last year where the owner's insurance company mandated the installation of an intelligent water shutoff (we installed Moen's Flo valve in both homes.) That might provide reasonable protection, but putting the water heater in a garage is a pretty simple preventive measure. If only we could do that with refrigerator ice maker lines....

I'm no expert, but LOVE having hot water in 8 seconds at any faucet in the house. A recirculating pump was part of our build 20 years ago. It's an *everyday luxury*. Saving water is nice, but not THE reason I'd miss this.

Note: If you have one, remember to turn it off anytime your water has to be shut off for a while or the pump will burn out. (Our city reimbursed us for a new pump for not notifying us of a several-hour shut off while they were working on pipes.)

Interesting…

I’m seeing a pretty strong no-go on the attic. I personally never liked hanging on an outside wall as stated above (even if they match up stucco etc).

We eventually plan to have propane standby power for basics.

The PEX water lines are going in the attic. The last sub in the area no longer offers in-slab plumbing.

How about this - Tankless in broom closet in laundry rm next to master suite?

• Put a tankless in the broom closet off the laundry rm near master. It’s 2 ft deep but over 5.5+ ft wide (it’s an irregular parallelogram shape). Could stick smaller shelves perpendicular on 1 side and open up back and other side to bare wall to mount too?
• This is where the internet comes in and a network switch for CAT5 to other rooms - should I be concerned about heat from tankless in there?
• Can put a drain in floor (just need to keep scorpions and widows and such out)
• Would all be on interior spaces and require the appropriate venting out the wall or soffit or roof. But pretty close to master bath (and washing machine).
• Could still throw a smaller 2.5 ga POS tank under the vanity for lag from tankless if really wanted that instant-on effect.

(Iikewise could instead put tankless in master closet at furthest end of house)

Consider getting the navies with the built in recirculating pump. That’s what we have and water gets hot in 4 seconds without needing any extra button.

Charles - I was thinking of a sealed, insulated attic. That is what I have. There is very little freeze risk unless there was extended empty house + extended electric shutdown + cold snap not seen before. It happens to be on the south side so stays a little warmer than the house.

OP - propane is something we will be phasing out. There will likely be an alternative and it will be more expensive. Try not to corner yourself into using something that if you have an alternative. Especially not for day to day use. Tankless electric is a poor choice.

@David Cary,

I suggest care when making general conclusions or recommendations based on your specific experience, unique construction methods in your home, and what works in your particular climate zone. Conditioned attics (I've built only four homes with them) are atypical, at least in our area.

Insurance companies are good at quantifying risks, and learning how to mitigate potential losses. While it's not the norm, two of my clients--both of whom were insured by Chubb--were required to have an intelligent water shut off valve installed in their homes. The insurance company inspected the home during construction and at completion to ensure the required shut off valve was installed and operational. Given the low cost of intelligent shutoff valves compared with potential losses caused by water damage, I suspect we'll see more insurers requiring them in the future.

Our hot water tank was installed April 2017. It is being replaced Monday because it is leaking! Thank goodness it is in the cellar!

​​There's no dimensions but one option would be to lengthen your laundry room and put it in a utility closet in there, that would center it between your everyday needs and help with timely distribution.

Just FYI:

There's virtually no heat thrown off by the tankless heater.

You do need a drain for it - both for the condensate and the T&P valve. You also have to flush it.

I think they all have outside air intake - so that's not an issue.

You can sidewall vent that - it's better than going through the roof unless that's the front of your home.

I still think a hybrid in the garage would be a way to go. So much cheaper than propane.

Here's a pic I snapped of the actual laundry room with the odd shaped broom closet. It's currently 2 ft deep and about 5 ft 6 in wide. It could be made slightly deeper - maybe 2 ft 6 in. Or the broom closet door could float left/right along the wall a little.

Lots of permutations and tweaks. I photochopped a few options (but there's more I can think of). Those are interior walls around the closet.

Could also put it on the wall on right side just past where the laundry door swings (3rd pic on bottom). It would be 'exposed' mounted to the wall and might hamper moving equipment in/out. That's an exterior wall.

Thoughts on any of these?

It looks like there's options for condensing or non-condensing models. I guess a non-condensing model doesn't require a drain? (they are getting ready to set forms in a few days so need to decide if I need a drain pretty quick if I'm going to try for one inside the house vs on outside wall)

Either one in the closet would work, I would consider what your putting in there, mop, bucket, vacuum cleaning supplies, etc, but it looks like putting it to the right might give you more wall/floor space.  You could start your shelves 3 1/2 - 4 feet off the ground to accommodate the vacuum if needed.  You could also utilize the back side of the door for broom and dust pan.

Basically I'm now looking to requesting the builder go with an indoor unit in the broom closet (one of the options w/ 'red' box above).

If so, will need to decide between a condensing (need to add a drain or tie into the washer drain) or non-condensing (have to be more careful on venting due to hot vent pipe I think.

One of the new issues I have w/ the outside unit is that now the slab on the back will be fairly deep - that will certainly put an outdoor unit above my shoulders if not entirely over my head - for maintenance (or replacement someday) I REALLY don't like that at all.

Any FINAL WORDS of caution before going into contractor w/ request to locate an indoor unit in broom closet of laundry near master? (condensing or non-condensing)

thanks

If you select a tank type, consider a drain. They have a pressure relief valve that could let go and also can spring a leak later on in life.

Condensing is the only way to go because you can vent with PVC instead of the required Stainless steel for non-condensing.

You have to have a drain for the relief valve.

Determine for each type the back-draft pressure that must not be exceeded. It may affect your kitchen hood make-up air system complexity unless you allow outside air to go into these closets to the units such that they see only outside pressure. In other words, tiny but low restriction MUA paths to the water heaters can save a lot in kitchen MUA complexity.

The burner ratings of tankless hot water heaters are comparable to some gas furnaces; they can consume a lot of combustion air. To be sure, the potential for back drafting to occur should be considered when installing non-condensing type tankless hot water heaters in living spaces. However, condensing-type tankless hot water heaters are sealed combustion units with a dedicated pipe to supply outside air for combustion air and a dedicated exhaust i.e., no potential for back drafting to occur.

The btu input on a typical tankless gas water heater is actually equivalent to about two furnaces. A typical tankless water heater is 200,000 BTU per hour. A typical gas furnace for larger house is 100,000 BTU per hour. Don't mess around with anything but a sealed combustion setup. Go with the condensing unit and outside air intake. You have to put in a drain no matter what

The BTU rating of a furnace depends on the size of the home and the climate zone. For a 3,500 SF home in our climate zone (zone 4), a furnace would be rated around 160K BTU/hr. which is pretty close to the same 180K BTU/hr. rating as a 7.5 gpm condensing-type tankless hot water heater. The furnace rating would be higher for the same size home in colder climates and lower in warmer climates. In any case, the amount of combustion air consumed by a tankless hot water heater is sufficient that it needs to be considered in the design phase. I wouldn't put a non-condensing hot water heater inside a home.

I am happy to learn that condensing units universally have their own MUA. I hope that they are sealed well enough to resist back-drafting if the room pressure is below the exterior pressure by several tenths of an inch of water column, which is possible with good kitchen hood potential performance but inadequate kitchen make-up air performance.

If servicing a Master bath with 1 shower, 2 vanity sinks (no tub) plus a washing machine (and small rarely used sink next to it) - what is a prudent capacity for a tankless? (the other parts of house are serviced by different water heater)

I could easily see a single sink and shower at same time. More rare might be clothes washer and shower or clothes washer and vanity.

thx

200k btu (199k). Always. There's no compelling reason not to - and the higher btu will give you plenty of headroom when there are multiple demands at the same time - particularly filling a tub in the winter. So that you know, tankless will modulate the burner down to the appropriate level for given inlet temp and water flow. If you exceed the ability of the heater to provide hot water it will reduce the flow of water so it can maintain outlet temp.

Pay attention to minimum flow rates to activate and to keep running.

Rheem has always been very good on the min flow rates, but check the brand you are considering.

"Pay attention to minimum flow rates to activate and to keep running."

Good advice. One of our clients was disappointed when the flowrate of the handheld shower for her freestanding tub was too low for proper temperature control by her tankless hot water heater.

That can also happen when the outlet temperature is set too high. There's rarely any reason for it to be above 115 F. If it's set too high then it only requires a small amount of hot water that then gets mixed down to 105 or so. Because the flow is so low the water heater shuts off.