Two water heaters, or recirculation system?

[RHinNorCal]

New house construction, wood frame over sealed/conditioned crawl space. It' will be about 80 feet from the tankless water heater to the kitchen sinks (only 15-25 feet from all three bathrooms). Not enough height in the crawl space for a heat pump water heater, unfortunately, so propane will be the fuel source.

Should I put a small second tankless unit on the kitchen wall, or will a small storage tank recirculation system give me good results without breaking the energy efficiency bank? California build, so water savings are a real consideration. Thoughts?

 

[Dana]

Install a local electric water heater for the kitchen, forget the recirculation loop.

Every time the loop runs you're abandoning nearly a gallon of hot water even if it's 1/2 inch pipe, about 1.5 gallons if 3/4 inch. Many hot water draws in a kitchen are taking less than a gallon, which would short-cycle the tankless at low efficiency too.

Is energy in the form of propane even cheaper than resistance electricity in your local market? In many markets in OR/WA condensing propane is pretty much at parity or more expensive than electricity, but they don't have the steeply tiered electricity rates common in parts of CA.

Is there a garage where a heat pump water heater would fit, eliminating the propane burner? Even if it's 80 feet from the bathrooms and needs a 3/4" recirculation loop, bathing draws are large in comparison to the loop volume. It might take an 80 gallon tank and a drainwater heat recovery unit to serve three bathrooms (assuming no large spa tubs to fill), but at the operating cost of heat pump water heaters even tub-fills are likely to be cheaper (and definitely faster) than a condensing propane tankless, and with even a 4" x 48" drainwater heat recovery unit showering costs would be even less (and the "apparent tank volume" even bigger.)

 

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[RHinNorCal]

In Sonoma County, propane is a little higher than national average. Garage is, unfortunately for hot water, almost 150 ft from the kitchen and 200 feet from the bathrooms. I thought about excavating a small "pit" for a heat pump water heater, and looked for 'lowboy' heat pumps but didn't come up with anything that would fit in a 48" tall space. There are no outdoor units, so that's out. Tankless seems to be the best option; most of the time, only one bedroom will be in use, so there won't be all that much usage even considering the (well insulated) hot tub.

A small (6-7 gallon?) electric resistance heater for the kitchen isn't a terrible option considering that I will have a 6-7kw solar array and have space for more in the future.

 

[Dana]

The small electric tank for the kitchen is the right solution if going tankless for the baths.

The SAN-43SSAZU 43 gallon tank for the Sanden heat pump water heater is only 37-1/8" tall (dimensions on p.30). The compressor lives outside, not on top of the tank. But even at a storage temp of 175F (which it's capabable of) might not be enough if there are three bathtubs. I don't know if there's an easy way to use two of the shorter 43s with that unit.

If yours mostly a showering family with no big soaker-tub/spas to fill the 43 gallon Sanden at a high storage temp in combination with a 4" x 36" (or taller) EcoDrain V1000 would cover it.

 

[Jadnashua]

With a crawl space versus a basement, there probably isn't enough vertical room for a drain water heat recovery system.

Many hot water uses are short duration, and not great for operation with a tankless system. Only some tankless systems can be reasonably integrated with a recirculation system. You have not only the delay to trigger the tankless to come on and come up to temp of the heat exchanger, you have to purge the line, and then, if you're only interested in warm water, you may not trigger the minimum flow sensor to even turn the tankless system on.

They have their place, but they are not as transparent as people might think having grown up with a tank. Are you willing to relearn how to use hot water?

 

[Dana]

With a crawl space versus a basement, there probably isn't enough vertical room for a drain water heat recovery system.

Even a 36" drainwater heat recovery unit can hit 50% recovery at 2.5gpm if going with the Ecodrain V1000 series. (That beats my 4" x 48" Powerpipe's performance by a hair.)

RHiNorCal reports a 48" tall crawlspace, which should be enough room.

If for some reason that doesn't quite make it, a 30" PowerPipe delivers 37% recovery at 2.5gpm, which is enough to make a noticeable difference in apparent capacity for a tank, and would almost surely fit.