Author Topic: Hybrid Water Heater  (Read 461 times)

kenmoremmm

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Hybrid Water Heater
« on: January 10, 2019, 09:52:19 PM »
Our water heater is nearing the end of its useful life and it's starting to show in the amount of hot water we're getting. I'm considering a hybrid water heater: https://www.homedepot.com/p/Rheem-Performance-Platinum-50-gal-10-Year-Hybrid-High-Efficiency-Smart-Tank-Electric-Water-Heater-XE50T10HD50U1/303419574

After a $500 rebate from the local power company, it's only $250 more than a standard water heater for the 50 gal tank, so it's a no brainer even with the goofy plumbing line locations and the added hassle of condensate.

However, I think we're on the border between 50 gal and 65 gal based on expected usage. We will soon have 2 kids. I take 3 min showers; my wife is around 8. Low flow showers. Efficient d/w and washer. I feel like most of the time we should be well-served by the 50, so I'm leaning that way. However, I understand that in heat pump mode, the unit only heats 8 gal/hour compared to 20 with electric resistance.

We're in the Puget Sound area, so maritime climate. Winters could be a challenge for the unit to heat quickly enough, and of course, this is when you want the water the most. I'm curious if anyone out there has installed this model and has opinions on size. My gut tells me that 98% of the time we'll be just fine with 50 gal, which obviously screams to get the cheap one. But, water heaters are more efficient with larger tanks, so the maintenance costs could pencil out vs. purchase price assuming the thing lasts 10+ years.

Prairie Stash

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Re: Hybrid Water Heater
« Reply #1 on: January 11, 2019, 10:39:52 AM »
If you have the time to onsider a drain water heat recovery unit, it cuts down on the size of tank needed. It transfers the heat from your drain to the cold inlet water to the tank while you shower.

Check your power company to see if theres rebates, its a good way to cut electric power costs. The payback only works when you heat with electric, I have gas and my hot water costs are about $80/year, I don't have one but I would if I had electric hot water.
https://www.energy.gov/energysaver/water-heating/drain-water-heat-recovery

Put it down as option C, a smaller tank with a heat recovery unit to increase the amount of hot water available at peak usage times.
https://www.homedepot.com/p/Power-Pipe-3-in-x-36-in-Drain-Water-Heat-Recovery-Unit-R3-36/203455990

kenmoremmm

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Re: Hybrid Water Heater
« Reply #2 on: January 11, 2019, 10:52:47 AM »
my main drain is buried behind a wall and then it drops into the basement floor slab. i don't see this option working out well.

BudgetSlasher

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Re: Hybrid Water Heater
« Reply #3 on: January 11, 2019, 05:33:58 PM »
We have a Rheem which allows you to set the temperature higher than is "safe."

What we did was start with an oversized, for us, tank to allow us to run in heat pump only mode. Then we dialed up the tank temperature to ~138F and installed a mixing valve set to 120F on the output. Effectively our 80 gallon tank can put out more than 80 gallons at 120, how much more depends on incoming water temperature (which varies greatly by season).

When I purchased I did not see a 65 gallon option available and while we probably would have been fine with a 50 gallon tank, around here for a house with our layout a 50 gallon would be undersized and many people are used to unlimited hot water coming off of the boiler.

kenmoremmm

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Re: Hybrid Water Heater
« Reply #4 on: January 11, 2019, 05:41:01 PM »
yeah, that's kind of my thought too. if it's not kicking out enough hot water, then we just up the temp (which loses efficiency). first hour rating on this is 67 gallons, so i struggle to see a normal situation in my house where we exceed that.

BudgetSlasher

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Re: Hybrid Water Heater
« Reply #5 on: January 12, 2019, 09:34:03 AM »
yeah, that's kind of my thought too. if it's not kicking out enough hot water, then we just up the temp (which loses efficiency). first hour rating on this is 67 gallons, so i struggle to see a normal situation in my house where we exceed that.

Do take a deeper into the conditions of that "first hour" rating and your situation and how you will set it up and what your climate is like.

I can almost guarantee that number is not running in heat pump only mode and it may be running in one of the higher demand modes(ours goes something like heat pump only, high efficiency, hybrid, high demand, and all electric; it is a scale of never use the electric element to never use the heat pump). That may not be an issue for you, but we chose to run in heat pump only which means lower first hour numbers in exchange for more efficiency. You may also want to look at your local conditions vs the first hours numbers; our basement is ~54 all winter (due to "waste" heat from the boiler) and maxes out in the upper 60s during the summer probably not the test conditions for their first hour numbers.

Edit: I forgot the mention that the first hour rating also assumes a certain incoming water temperature, which our well water was below, especially in the winter.
« Last Edit: January 12, 2019, 03:19:36 PM by BudgetSlasher »

FiftyIsTheNewTwenty

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Re: Hybrid Water Heater
« Reply #6 on: January 13, 2019, 01:58:12 PM »
^^^ Are specs available for all the stages from pure heat pump through hybrid to electric element?  Can we set the modes?  It may be worth buying a bigger one to stay in heat pump mode.

Good point about input temperature.  If 70 deg water takes 4-5 hours to heat, then 50 deg water might take all day (for example).

Though compared with most households we're not big users of hot water, it's still a good chunk of a power bill ($50 or so for us).

BudgetSlasher

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Re: Hybrid Water Heater
« Reply #7 on: January 13, 2019, 06:43:32 PM »
^^^ Are specs available for all the stages from pure heat pump through hybrid to electric element?

I do not believe that the specs are published by the manufacturer for every mode. If you look their may be a DOE study that has deeper information.

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Can we set the modes?  It may be worth buying a bigger one to stay in heat pump mode.

On my Rheem I can set the mode and keep in heat pump only mode.


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Good point about input temperature.  If 70 deg water takes 4-5 hours to heat, then 50 deg water might take all day (for example).

Our incoming water temperature can drop to sub-40F in the winter. So far running in heat pump only mode we have only had 2 times in 2 years (with 2 people) that hot water has been an issue. And those have been days with 6+ loads on laundry and a lot of hand washed dishes, or days where the utility sink was used a lot (no flow restriction).

We receive occasional of "trouble satisfying demand" "alarms" or notices on the hot water heater, but I, as the last person to take a shower at the end of the day do not notice a drop off in hot water.


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Though compared with most households we're not big users of hot water, it's still a good chunk of a power bill ($50 or so for us).

We switched from an indirect tank off of a boiler which had issues, both supply and efficiency, most likely due to stratification, scaling, and improper plumbing diameter to our hybrid and did not notice a large increase in kwH (we also changed to a heat pump clothes dryer at the same time so that probably pulled power usage down). This was also done in anticipation of installing a solar array.

SweatingInAZ

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Re: Hybrid Water Heater
« Reply #8 on: January 14, 2019, 10:36:20 AM »
Our water heater is nearing the end of its useful life and it's starting to show in the amount of hot water we're getting.

When was the last time you drained your water heater?

Checked the anode?

kenmoremmm

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Re: Hybrid Water Heater
« Reply #9 on: January 14, 2019, 11:36:14 AM »
drained 2 years ago. checked anode, never. it's 12 years old. theoretical cost savings will more than pay for the new unit in <3 years, so as long as there are no problems, it's a good choice anyway (i hope).

SweatingInAZ

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Re: Hybrid Water Heater
« Reply #10 on: January 14, 2019, 06:42:49 PM »
drained 2 years ago. checked anode, never. it's 12 years old. theoretical cost savings will more than pay for the new unit in <3 years, so as long as there are no problems, it's a good choice anyway (i hope).

Someone had to ask :)
Sounds like you've done your homework.

m8547

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Re: Hybrid Water Heater
« Reply #11 on: January 15, 2019, 01:58:11 PM »
I think you'l be fine with 50 gal. You might need to make some slight adjustments to when you use hot water to maximize heat pump usage vs resistance heating. With low flow and high efficiency appliances it seems like would be hard to use up a 50 gallon tank. And if showers become a problem you can put in even lower flow shower heads. I have a 1.5 GPM High Sierra shower head, and it's great. It uses a lot less water than a standard 2.5gpm "low flow" shower, and I don't miss the extra water.

You can use the timer feature on your dishwasher and laundry so those run at night or mid-day after the heater has recovered from showering.

As an experiment, try turning off your water heater and see how long you can go before the water gets cold.

I'm thinking about putting in a 50 gallon unit myself, so I'm interested in any discussion about them. I would like to know more about how they really work, for example if the outside temperature is 37 degrees (the minimum for heat pump mode IIRC), can does the heat pump still heat as fast as if it's warmer outside? I can't imagine that it would. And it's hard to imagine that it could take icy cold incoming water and heat it to 120-140 using only a heat pump and 37 degree ambient air, while still being much more efficient than resistance heat. It might not be a problem for me anyway, because waste heat from my boiler keeps the utility room at a toasty 90-100 degrees F all winter.