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Before I get too excited about a new piece of technology did you only find these for electric water heaters or do they make ones for gas heaters too? The de-humidifier aspect is very appealing. Especially in our very old home we run one to two dehumidifiers all summer long. Working on other things to reduce that need but still it's huge and bad.

Marc Rosenbaum

I think one of these could be adapted to a gas water heater. If you are on natural gas, it's likely that the cost of making DHW is less than with a HPWH, though.

Heating and Plumbing

Excellent job done, I am completely impressed by your work. It's quite a big heater but you managed it easily.


Marc, the link to the report does not work.

Marc Rosenbaum

Thanks for the feedback on the link, please try again now.

Jordan 11

I think one of these could be adapted to a gas water heater.

j chesnut

Thanks again for going into such detail. I particularly appreciate the information about how you are metering and collecting data.

Any chance that the HPWH is cooling the air enough to bring the adjacent part of the concrete slab under the dewpoint causing the puddle under the 5g pail?

Marc Rosenbaum

Good thought, j chesnut, but I can see the water dripping onto the stand first...

 Canada Goose

in the middle of the summer, when the basement temperature and relative humidity was highest, there was a puddle on the concrete below the unit, which went away as we left the peak cooling season behind. I tried to determine the issue and the folks at Nyle were very helpful, but in the end I think that somehow there is a leak in the drain pan, probably at the corners, that only is operative when the rate of condensate is high. Alternatively, there may be condensation on a component that is not above the drain pan. I may need to wait to next summer to resolve this one.

Bob Lemaire

Marc, I was curious why you chose to use the lower element fitting for part of the heat pump loop. Marathon recommends using the drain plug and cold water inlet when connecting to a heat pump. I realize that the lower element is useless to you anyway (and the upper for that matter) but is there some efficiency consideration?

Marc Rosenbaum

The Marathon is configured so it's not possible to use the tube-within-a-tube fitting that Nyle supplies. I could have brought the heated water into the cold water dip tube as well. Since that water can be quite cool in the earlier part of the heating cycle (say you've just drawn off 10 gallons and the bottom of the tank is 55F - the heated water coming from the heat pump might be 60F) I didn't want to bring it down through the hot water at the top of the tank. Does this make a lot of difference in terms of efficiency? Probably not. But I don't want the water temp at the tap to be lowered by this effect, so I played it safe.

Erik Haugsjaa

Marc, we also have a Marathon (105 gallon) and a Geyser setup going on 1 year in our conditioned basement. I find it a little loud (home office in the open basement) so I have it on a beefy $10 timer to run on off-hours. The only time we run into problems is when we have 3+ kid baths happening back to back... (we are 8 people... 4 kids at the moment). If I know this is coming up, I turn on the resistance elements ahead of time which are set a little hotter and recover faster.

We had a similar puddle once.

I need to do your hack to help keep things better stratified. Nice.

My calcs are that we have 100% solar fraction (net) solar hot water via slightly larger PV array and the geyser. For same price as a traditional solar hot water system (at 60-70% fraction).

One other thought I've had:
The 120V Geyser (often running around 700W) might come in handy during a power outage since any generator or solar backup wouldn't easily handle the 220V resistance elements -- 4500W.

Hal Levin

This is a great conversation for someone like me considering adding a HPWH. My interest is in using a HPWH for heating water for a couple of radiators to heat the house. I already have solar DHW and my house is all-electric with an electric energy cost of minus $27 last year, thanks to my PVs, a time of use meter, careful timing of my electricity use, and a generous peak period rate about 3x the off-peak rate from PG&E. My solar DHW system provides all my DHW needs for the warmer (sunnier) part of the year on California's Central Coast. It provides a small contribution to DHW needs during the cooler and cloudier part of the year.

I am very concerned about the noise factor since the HPWH COP is highest with higher air temps, so I want to install it within an enclosed space inside the structure. (No attic or basement in this house.)

So.... have either of you (Marc or Erik) actually measured the noise level and, if so, can you give me your numbers? My solar DHW system provides all my DHW needs for the warmer (sunnier) part of the year on California's Central Coast.

On a different note, for those self-helpers with attics, an integrated passive solar hot water heater system might be the answer. If you install the usual two-tank system below the roof in the attic and cover it with a high performance skylight (high solar heat gain coefficient, low emissivity) directly in the plane of the roof, you can avoid drain down, pumps, and a certain amount of piping. However, in cold climates, the night time losses may be large so an operable shutter or other insulator should be installed for use at night.

Marc Rosenbaum

Eric, how do you have the Geyser piped - through the cold water dip tube? And what are your solar calcs? Do you have gallons and kWh measured into the tank, including the resistance elements? Note that my set-up gives up the lower element.

Bob Lemaire

Hal, Seems to me that using a HPWH inside the living space to heat radiators is a something like leaving the refrigerator door open to cool the house. You might be better off with something like a Daikin Altherma outside.

Jan Juran

Hi Marc: If you have enough vertical drop from the shower drain to the main exit drain pipe to the septic or sewer system, you may be able to install a gravity film exchange drainpipe device. One GFX film heat exchanger can handle all the showers in the house if you can "gang" the shower drainpipes together into one drainpipe. One 5 foot long 3 or 4 inch diameter GFX should be able to save and recycle just over 50% of the heat BTUs used for showers. No moving parts, passive technology, lasts essentially forever. (I want to install one in my house however the mostly single floor design makes it difficult to get enough vertical drop without putting in a float switched pump which can eventually fail and need to be diagnosed then replaced).
If you have implemented a low energy dishwasher, cold water washer etc. then the GFX drainwater heat recovery device could recapture most of the hot water BTUs in your house, bonus=double the first hour capacity of the HPWH in case of many guests, etc.
Check out www.gfxtechnology.com also there are some competitors sold at big box retailers such as the Power Pipe.
Best regards

Marc Rosenbaum

I've used a bunch of drainwater heat recovery systems and I do like the PowerPipe design best. We don't have the drop in the basement because the graywater line exits near the top of the foundation wall. We could put one with some effort in a first floor closet and it would serve the upstairs shower, which we use more often. If I were doing new construction I'd integrate it into the system, as a retrofit in this case the effort seems more than its worth.

Jan Juran

Hi Marc: my house has the same retrofit problem, insufficient vertical drop in the basement. Perhaps if one of the manufacturers (i.e. Power Pipe, GFX) might make a "retrofit" version, with a float switch activated pump at the bottom which returns the drain water up to the same elevation (via a PVC pipe) as the device's drain water intake? Drainwater heat recovery products can save a terrific amount of wasted heat BTUs, very cost effective over time.

Marc Rosenbaum

That certainly could be done. I have a strong reluctance to interfere in any process where gravity is providing the needed service for free though!

Jan Juran

Hi Marc: very true, that is a very important consideration. The failure mode here would still drain correctly and for free, passively via gravity, if the pump failed (power failure, pump eventually burns out, etc.) The drainwater heat recovery system simply temporarily would become in effect a second larger S trap; the exhaust point of the loop would be an inch or several inches lower than the input point of the DHR system "loop"--a benign failure mode.

Richelle Loughney

I'm planning to replace our water heater tank for our apartment, and we may choose that one since we are so many here. Thanks for the installation tips.

Jan Juran

Hi Marc: BTW I recently swapped out all the showerheads in my house with the Niagara and the AM Conservation 1.25 gpm non-aerated models. I cannot discern any difference re quality of shower compared with the old 2.5 gpm standard showerheads. Simple way to approx halve the water usage, halve the heat BTUs used, double the HW heater capacity for showers, and extend the est. life of both the septic system and HW heater. Efi.org carries the AM Conservation 1.25 model for $5.

Marc Rosenbaum

Which of the two showerheads did you prefer?

Jan Juran

Both the Niagara and the AM Conservation 1.25 gpm models work well. I like the Niagara a little bit better, also I prefer the look of the chrome Niagara vs. the white AM Conservation.
I also swapped out the bathroom sink faucet aerators for 0.5gpm and 1.0 gpm models. The flow of the 1.0 is more than adequate, while the 0.5 flow is a bit less than adequate. Have been looking for something in between, but cannot find a manufacturer making a 0.7 (or thereabouts) gpm faucet aerator.

Marc Rosenbaum

Take the 1.0 aerator and make an insert from a piece of copper flashing that restricts the opening a bit.

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