Opinions on This Plan to Replace an Electric Hot Water Heater
I am thinking of replacing my 20o2 80gal electric HWH. My guess is it is not that efficient and may leak at some point. It seems that that size is no longer made due to efficiency requirements, and instead a hybrid heat pump/electric version is my best option without gas service.
However, the HWH sits in my first-floor bathroom next to the washer and dryer. The area is unheated, and so having had hybrid HW heaters in other living locations I know that efficiency-mode will steal significant residual heat.
My solution is to avoid ducting to and from the crawl space, and instead to only run it on efficiency/hybrid mode from May to October, and then run it in electric-only mode in the winter. Is this a feasible workaround? Are there any downsides to my method?
With rebates, the cost of this https://www.homedepot.com/p/Rheem-ProTerra-80-Gal-10-Year-Hybrid-High-Efficiency-Smart-Tank-Electric-Water-Heater-with-Leak-Detection-Auto-Shutoff-XE80T10HS45U0/312741448#product-overview seems like a decent deal.
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Replies
Where are you located?
Northeastern PA. Zone 6.
trapdoor,
Personally I would go with a standard 240v electric rather than the HPWH. The one you cited is $1800 before rebate, a Westinghouse 80 gal is $1300 and the Rheem 75gal is ~$1300 as well. I have an 80 gal Marathon plastic tank that is a bit harder to find. Your in bath/laundry location could make the fan noise and cool air output problematic to live with. You are on the right path about using "unpaid for" heat during warm months and not paying "pump fees" to steal the heat you paid for to heat the house. Any laundry heat or bath heat that might be harvested will be trivial. Besides, the fan unit is most likely to come on just as you finish your shower due to the hot water demand. Cold air blowing around the bathroom would make for a bracing end to your shower.
You think your current heater is inefficient. Have you ever flushed it or attempted to de-calcify the tank and heater loops? Being 18 years on it may not be a worthwhile effort. I once replaced an electric with a gas heater (since I did have gas available). After draining the old electric I soon discovered why my hot water supply gave out so quickly. The drained heater still weighed an enormous amount. After dragging it into the yard, I cut into it for grins and giggles to find a 2-3" coating of rusty crud on the sides. The heater rods looked equally bad.
The relevant point is that hard water will also take its toll on a HPWH albeit more slowly since the heat coils from the heat pump section generally wrap around the tank body. The resistance loops are not active as frequently as a straight up resistance HWH so the rate of build up would be slower with the HPWH.
I am guessing you at least have a winter where you are, so planning on ducting into your crawlspace is probably not going to yield great heat value. Crawlspaces generally don't run as warm as the house, so your feed air might be close to the lower limit of the HPWH unit. I think most have a cut out feature if the feed air drops below 45. Ducting will also tie up space where the heater sits.
The ability to force only resistance as a setting may or may not be programmable. The resistance heaters are usually programed to assure adequate rise rates and output. Forcing an only heat pump mode typically means longer recovery times. If you can download the manual for a unit you can sometimes figure out what kind of cycle life the resistance heaters will have.
While the HPWH shout out COPs of 3-4, the values are not quite what they seem. These values are often for best conditions and only refer to the efficiency of the pumps moving BTUs not creating them out of thin air. All COPs drop as the tank temperature rises and if you have cold feed air conditions for extended periods, the resistance mode will eat into the overall efficiency. I have seen some analysis that suggests overall efficiency can be as low as 1.75 times that of regular HWH.
Electric only is a standard mode on all the hybrid heat pump water heaters I've looked at.
They also don't specify COP. They use something called EF (energy factor), a nebulous term that I suspect has the specific purpose of making people think it's actually COP.
Is there any efficiency difference between a hybrid running in electric mode and electric hot water heater?
It seems like a dumb question, but if the answer is no. Then I am likely better off with the hybrid which I can run in various modes depending on the season. The rebates offered by my electric supplier ($400) and federal gov ($300) result in the cost of a hybrid being equal or less than an standard electric.
Electric-only mode is electric resistance heating without the heat pump part running. This mode essentially turns the HPWH into a "regular" electric resistance water heater. Electric resistance heat is essentially 100% efficient, so all the losses are heat leaking out through the insulation around the tank -- exactly the same as what happens with a "regular" electric water heater.
The short answer is that your HPWH running in electric-only mode is the same in terms of efficiency as a regular electric water heater would be.
Bill
As long as I can force the unit to stay in that mode, it seems like a hybrid would be the way the go.
The hybrid heat pump will have some additional electronics versus an old school electric, but that additional electricity will be negligible. Whichever model has the better tank insulation will have the lowest power usage during electric only mode. That's not a published spec, so no point in giving it much thought.