Hybrid Electric Pump Water Heater in Northern Climate?

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Fordguy88
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Hybrid Electric Pump Water Heater in Northern Climate?

Post by Fordguy88 »

Does anyone on here have experience with installing an electric pump water heater in their basement in a northern climate zone (WI,MN, Michigan, Dakotas etc) and what the electricity savings/actual usages were?

My basic understanding is you install these and they extract the heat out of the ambient air and use it to heat the water. Annual electricity costs would be $120 per year versus my current 80 gallon old water heater that is about $600/year. With the fed rebate this would be $1300 before install. Average water heater is $500 so the pay-off would be 2 years.

This type of water heater would make sense to me to install in the South in the garage where there's ample heat to pull in, but what about in the northern climate zones in a basement that is generally going to stay in the 60 degree range all year long +/- 10 degrees at the very most.

https://www.homedepot.com/p/Rheem-Perfo ... 81#overlay

Thanks in advance for any thoughts you can share,

Fordguy88
Wellfleet
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by Wellfleet »

Do you have a boiler throwing off heat that the heat pump could extract in the winter? Otherwise your basement will be quite chilly in winter.
talzara
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

Fordguy88 wrote: Fri Sep 17, 2021 10:17 am My basic understanding is you install these and they extract the heat out of the ambient air and use it to heat the water. Annual electricity costs would be $120 per year versus my current 80 gallon old water heater that is about $600/year. With the fed rebate this would be $1300 before install. Average water heater is $500 so the pay-off would be 2 years.
Water heaters are tested at an air temperature of 67.5°F, a supply water temperature of 58°F, and a setpoint of 125°F.

The Rheem XE50T10H45U0 heat pump water heater has a rated Energy Factor of 3.75. In your climate, you should expect to achieve an Energy Factor in the 2s. You'll get a payback in 3-4 years instead of 2 years.

Keep in mind that the rating is for a 50-gallon water heater. You are replacing an 80-gallon with a 50-gallon. If you draw that much hot water at one time, a 50-gallon unit will not be able to recover using only the heat pump.
BreadandButter
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by BreadandButter »

In your climate most of the ambient heat used by the water heater will probably come from your heating system. It will work a bit harder to heat the house to provide this heat. This will raise heating costs a bit, which reduces the benefit of the heat pump water heater. This is hard to quantify though.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by dratkinson »

BreadandButter wrote: Sat Sep 18, 2021 11:07 am In your climate most of the ambient heat used by the water heater will probably come from your heating system. It will work a bit harder to heat the house to provide this heat. This will raise heating costs a bit, which reduces the benefit of the heat pump water heater. This is hard to quantify though.
+1

I was considering replacing my old WH---NG, standing pilot light, normally aspirated, no moving parts. My home heating is NG forced air, normally aspirated.

I remembered this from a HS physics class. Energy can be transformed from one type to another (mechanical, electrical, chemical, heat,...). But every transformation results in a net loss of total energy. A heat pump WH inserts a mechanical transformation, for what was direct NG consumption.

If I changed to a heat pump WH:
--My home NG heating bill must rise to offset any NG savings from replacing a NG-fired WH.
--My home electric bill must rise for that consumed by the WH's heat pump, and for my home furnace running longer.
--And I now have a WH with a heat pump's moving parts---another point of failure.

So I opted to put in a new NG, standing pilot light, normally aspirated WH. It's major benefit is it's simplicity and it'll work during a power outage; so I can take a hot shower and jump in bed.


If (a heat pump's) electric consumption were efficient, most would use electric heat. But we don't because NG heat is reported to be more efficient. So any transformation(s) that get between direct NG consumption, and heat produced, I believe, must be less efficient.

I could be wrong, but am blind to any flaws in my logic.
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talzara
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

BreadandButter wrote: Sat Sep 18, 2021 11:07 am In your climate most of the ambient heat used by the water heater will probably come from your heating system. It will work a bit harder to heat the house to provide this heat. This will raise heating costs a bit, which reduces the benefit of the heat pump water heater. This is hard to quantify though.
Even in that climate, the heat pump will still be pulling heat from outside the house for 4 months a year. Minneapolis has a summer design temperature of 88°F, and the average temperature is above 67.5°F from late-May to mid-September.

For the other 8 months, the heat pump will be pulling heat from inside the house. However, it will be reducing heat loss to the environment by reducing the temperature of the basement. The heat pump will also be pulling less heat out of the house when its own COP is lower.

The OP should be able to achieve an Energy Factor in the 2s even after adjusting for increased space heating demand. It may be 2.0 instead of 2.9, but even at 2.0, the heat pump still pays for itself in 4 years.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

dratkinson wrote: Sat Sep 18, 2021 4:13 pm I remembered this from a HS physics class. Energy can be transformed from one type to another (mechanical, electrical, chemical, heat,...). But every transformation results in a net loss of total energy. A heat pump WH inserts a mechanical transformation, for what was direct NG consumption.

...

I could be wrong, but am blind to any flaws in my logic.
The flaw in your logic is that the first law of thermodynamics applies only to closed systems.

The house is not a closed system. It is exchanging energy with the environment. During the summer, heat is infiltrating through the building envelope. During the winter, heat is being lost through the building envelope.

Since you don't want to gain this heat in summer, and you don't want to lose this heat in winter, any of the heat that gets captured by the heat pump is free. Of course, the heat pump cannot actually capture all of this heat since its performance drops when it gets cold. That is why the OP's heat pump has a rated Energy Factor of 3.75, but the OP will only achieve an Energy Factor in the 2s.
dratkinson wrote: Sat Sep 18, 2021 4:13 pm If (a heat pump's) electric consumption were efficient, most would use electric heat. But we don't because NG heat is reported to be more efficient. So any transformation(s) that get between direct NG consumption, and heat produced, I believe, must be less efficient.
Heat pumps are more efficient than natural gas water heaters, even when the electricity is generated by burning natural gas.

A natural draft gas water heater has an Energy Factor of 0.6. The OP can expect to achieve an EF of 2.0 in that climate, and natural gas power plants are 44% efficient in the current US energy grid. 2.0 * 0.44 = 0.88.

Heat pumps perform even better in warmer climates, where the heat pump can actually achieve its rated EF. 3.75 * 0.44 = 1.65. The heat pump is 2.8 times as efficient as burning natural gas on-site!

Cost is the main reason that people don't use heat pumps when natural gas is available. Electricity costs a lot more than natural gas, 4-5 times as much in some states. You may be putting less carbon dioxide into the air, but you'll pay more for the privilege.
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dratkinson
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by dratkinson »

^^^ Thanks. That helps.
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brianH
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by brianH »

Unless you heat your home with electric resistance heat, even if the HPWH is 'stealing' some of that in the cold months, you probably still come out ahead on a $ basis. Mine is in an unfinished basement, so there's some geothermal benefits. I also get 'free' dehumidification during the Summer.

Most HPWH allow you to run in heat pump only or resistance heat only modes, so worst case, you could keep it on resistance heat during the Winter and it would be a wash with a regular electric tank. When I bought mine, the electric utility was offering a rebate (as well as the Federal credits.) It ended up being about $200 more than a regular electric tank, which would be paid for in the first year.
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Fordguy88
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by Fordguy88 »

We heat our home with Propane as we are in a country/rural setting. This year I contracted 1500 gallons at $1.50/gallon to heat the house.

It's a complete guess since this is our first year and the previous homeowner heated the house with the wood burner outside, but I don't have the time to cut down wood at the moment with 2 and 4 year old kids.

We too have an unfinished basement currently. Where do you vent you water heater in the winter time? Or do you always vent to the outside and pull from the inside?

The perfect setup to me would be to have the option to pull air from the attic in hot months or inside during cold months . And then exhaust outside during winter and inside during summer for free A/C? I have an existing whole home air ducting already in place, so I am debating the feasability of being able to execute this ducting idea. Thoughts?
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by NoblesvilleIN »

Since you say you heat with propane and are a rural setting, are you on a well? The incoming water temperature of your well water might impact the efficiency of your WH. I looked at a tankless water heater several years ago and our well water was too cold for it to work well. I also considered a heat pump WH, but decided to go with conventional electric because the water heater is under our bedroom and I didn't want the noise of a compressor running.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by Fordguy88 »

Correct, I am on a well also. It's an 80 foot deep well (pretty shallow compared to most around here being 500' deep +, but still a well).

Ours would be housed in a walled off utility room, but yes the compressor noise would travel upwards under my daughter's room.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by mervinj7 »

Fordguy88 wrote: Mon Sep 20, 2021 9:39 am Correct, I am on a well also. It's an 80 foot deep well (pretty shallow compared to most around here being 500' deep +, but still a well).

Ours would be housed in a walled off utility room, but yes the compressor noise would travel upwards under my daughter's room.
Is the utility room part of the conditioned space of the house? If it's a typical unconditioned below grade level basement, as somebody mentioned, you get a geothermal effect since it pulls heat from the surrounding ground. Folks keep mentioning that the HPWH will be "fighting" the furnace but I don't see an issue unless you are actively heating your basement. 60F +/-10F is a great range for operation and near ideal.
Don't overthink the ductwork. You don't need it if the installation space is large enough. You will need a condensate drain pipe, though.
Does ambient air temperature remain between 40°- 90° F year-round? (An ideal spot would be near a furnace in a basement that is very warm all winter or a garage in very warm climates.)
https://www.energystar.gov/products/wat ... iderations
Last edited by mervinj7 on Mon Sep 20, 2021 5:53 pm, edited 1 time in total.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by brianH »

Fordguy88 wrote: Mon Sep 20, 2021 6:56 am The perfect setup to me would be to have the option to pull air from the attic in hot months or inside during cold months . And then exhaust outside during winter and inside during summer for free A/C? I have an existing whole home air ducting already in place, so I am debating the feasability of being able to execute this ducting idea. Thoughts?
I don't have mine ducted.

I don't think these units are really designed for crazy ducting scenarios. The fan is not that powerful, so it won't handle long duct runs. The support for ducting (which newer units don't include without extra parts) is really just for units that are located in a tight closet or something to pull from a few feet away.

You're probably overthinking it. If you were to duct the output outside, you'd be creating a negative pressure in your house that would suck cold air in through gaps anyway. The money you'd spend hacking some crazy duct system would never pay back from the small amount of efficiency you might save. If you really want to go crazy, they make split system water heaters where you'd have the compressor outside (like a regular AC system) connected by refrigerant lines to the inside tank. They are extremely expensive and overkill.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by Valuethinker »

Fordguy88 wrote: Mon Sep 20, 2021 9:39 am Correct, I am on a well also. It's an 80 foot deep well (pretty shallow compared to most around here being 500' deep +, but still a well).

Ours would be housed in a walled off utility room, but yes the compressor noise would travel upwards under my daughter's room.
If you don't have access to Natural Gas, a HPWH is probably worth doing.

This is more true if you are heating by electric induction w a high electricity cost.

In the winter the "waste" heat is of course not wasted - it goes into rest of house. That said it is usually an expensive way to heat v natural gas heating. And I have a hot water storage tank (about 55 gal US) that really does not leak heat very fast (factory applied foam insulation, insulated feet etc).

In summer the reverse. But ACs are quite efficient, so an extra kwhr of heat probably costs something like 0.33 kwhr to get rid of it?

However the overall effect should be small. Unless you have a large family, or teenagers (teenagers are not Energy Star Compliant), you probably spend maybe 3000 kwhr pa on hot water? 5-10x that in heating and cooling your house.

I'd worry most about noise and vibration. It sounds like there is a clear payback case.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

Fordguy88 wrote: Mon Sep 20, 2021 6:56 am The perfect setup to me would be to have the option to pull air from the attic in hot months or inside during cold months . And then exhaust outside during winter and inside during summer for free A/C? I have an existing whole home air ducting already in place, so I am debating the feasability of being able to execute this ducting idea. Thoughts?
They're called inlet and outlet ducts. The term exhaust is not used because there are no no harmful gases in the air, as there would be for the combustion products from a gas furnace.

You should not cross the building envelope. If the inlet is drawing from the house, then the outlet should send air back to the house. If the inlet is drawing from the attic, then the outlet should send air back to the attic.

You can't use the attic air anyway because it'll still be too hot. The Rheem Performance Platinum water heaters only have a 4200 BTU/h heat pump, which is smaller than most window air conditioners. The manufacturer does not specify the temperature drop across the evaporator coil, but it's probably no more than 30°F. If the attic is 140°F in summer, you don't want to discharge 110°F air back into your house.

Using attic air could even be counterproductive. The manufacturer specifies an ambient temperature range of 37 to 145°F. If your attic gets hotter than 145°F, the heat pump will shut off!
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

brianH wrote: Mon Sep 20, 2021 12:03 pm I don't think these units are really designed for crazy ducting scenarios. The fan is not that powerful, so it won't handle long duct runs. The support for ducting (which newer units don't include without extra parts) is really just for units that are located in a tight closet or something to pull from a few feet away.

You're probably overthinking it. If you were to duct the output outside, you'd be creating a negative pressure in your house that would suck cold air in through gaps anyway.
The fan is powerful enough for this application. The manual says that you can have up to 25' of 6" flexible ducts or 65' of 6" rigid ducts. That's long enough to get from the basement to the attic, even in a two-floor house.

Air infiltration can be minimized by using balanced airflow. If the inlet is drawing from the attic, then the outlet should also go back to the attic. This will cool down the attic and reduce the heat gain to the rooms underneath.

I would be worried about exceeding the maximum air temperature of 145°F, but maybe the attic never gets that hot in the OP's climate.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

NoblesvilleIN wrote: Mon Sep 20, 2021 9:35 am Since you say you heat with propane and are a rural setting, are you on a well? The incoming water temperature of your well water might impact the efficiency of your WH.
Heat pump efficiency increases when the incoming water is colder. However, it will take longer to heat the water.

A larger storage tank will help to buffer the hot water draws. The Rheem Performance Platinum series uses the same heat pump and the same heating element on the 40-gallon model and the 80-gallon model. The only difference is the size of the tank.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by brianH »

talzara wrote: Mon Sep 20, 2021 6:08 pm
The fan is powerful enough for this application. The manual says that you can have up to 25' of 6" flexible ducts or 65' of 6" rigid ducts. That's long enough to get from the basement to the attic, even in a two-floor house.
I saw that in the manual, but I don't buy it. It's basically a computer fan. Based on some of your replies, you're in the industry. Would you warranty an install with 65' of 6" rigid duct into the attic to hack a few points of efficiency?
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by ncbill »

talzara wrote: Mon Sep 20, 2021 6:18 pm
NoblesvilleIN wrote: Mon Sep 20, 2021 9:35 am Since you say you heat with propane and are a rural setting, are you on a well? The incoming water temperature of your well water might impact the efficiency of your WH.
Heat pump efficiency increases when the incoming water is colder. However, it will take longer to heat the water.

A larger storage tank will help to buffer the hot water draws. The Rheem Performance Platinum series uses the same heat pump and the same heating element on the 40-gallon model and the 80-gallon model. The only difference is the size of the tank.
If there's room one can also add a tempering tank before the heat pump water heater.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by Valuethinker »

talzara wrote: Mon Sep 20, 2021 6:18 pm
NoblesvilleIN wrote: Mon Sep 20, 2021 9:35 am Since you say you heat with propane and are a rural setting, are you on a well? The incoming water temperature of your well water might impact the efficiency of your WH.
Heat pump efficiency increases when the incoming water is colder. However, it will take longer to heat the water.
Heat pump efficiency is inverse to the gap between incoming and outcoming water temperature?

So the bigger the gap, the lower the efficiency? (ie COP approaches 1.0 from above).

Could you explain why that is not the case, here? (not wishing to sound sarcastic or disagreeing - genuine curiosity that I have not understood something basic?_
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by Valuethinker »

talzara wrote: Mon Sep 20, 2021 5:59 pm
Fordguy88 wrote: Mon Sep 20, 2021 6:56 am The perfect setup to me would be to have the option to pull air from the attic in hot months or inside during cold months . And then exhaust outside during winter and inside during summer for free A/C? I have an existing whole home air ducting already in place, so I am debating the feasability of being able to execute this ducting idea. Thoughts?
They're called inlet and outlet ducts. The term exhaust is not used because there are no no harmful gases in the air, as there would be for the combustion products from a gas furnace.

You should not cross the building envelope. If the inlet is drawing from the house, then the outlet should send air back to the house. If the inlet is drawing from the attic, then the outlet should send air back to the attic.

You can't use the attic air anyway because it'll still be too hot. The Rheem Performance Platinum water heaters only have a 4200 BTU/h heat pump, which is smaller than most window air conditioners. The manufacturer does not specify the temperature drop across the evaporator coil, but it's probably no more than 30°F. If the attic is 140°F in summer, you don't want to discharge 110°F air back into your house.

Using attic air could even be counterproductive. The manufacturer specifies an ambient temperature range of 37 to 145°F. If your attic gets hotter than 145°F, the heat pump will shut off!
Is the saving anything more than marginal?

If you live in a winter climate the "waste" heat is simply a relatively expensive way to heat the house (electricity >> gas price).

If you live in a more southern climate then the additional heat added to the house (from the operation of the HP) is quite small, relative?
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

brianH wrote: Mon Sep 20, 2021 6:24 pm
talzara wrote: Mon Sep 20, 2021 6:08 pm
The fan is powerful enough for this application. The manual says that you can have up to 25' of 6" flexible ducts or 65' of 6" rigid ducts. That's long enough to get from the basement to the attic, even in a two-floor house.
I saw that in the manual, but I don't buy it. It's basically a computer fan.
It's only a 4200 BTU/h heat pump. It doesn't need a big fan.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by brianH »

talzara wrote: Tue Sep 21, 2021 6:17 pm
brianH wrote: Mon Sep 20, 2021 6:24 pm
talzara wrote: Mon Sep 20, 2021 6:08 pm
The fan is powerful enough for this application. The manual says that you can have up to 25' of 6" flexible ducts or 65' of 6" rigid ducts. That's long enough to get from the basement to the attic, even in a two-floor house.
I saw that in the manual, but I don't buy it. It's basically a computer fan.
It's only a 4200 BTU/h heat pump. It doesn't need a big fan.
Yes, with no duct work, but you quoted the manual back at me implying that it would operate fine with 65' of ducting to an attic space. I highly, highly doubt that it would in the real world.

Since you seem to have experience, would you accept the risk of a callback due to a frozen coil when it can't get the airflow with that anemic fan?
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

Valuethinker wrote: Tue Sep 21, 2021 5:34 pm
talzara wrote: Mon Sep 20, 2021 6:18 pm Heat pump efficiency increases when the incoming water is colder. However, it will take longer to heat the water.
Heat pump efficiency is inverse to the gap between incoming and outcoming water temperature?

So the bigger the gap, the lower the efficiency? (ie COP approaches 1.0 from above).

Could you explain why that is not the case, here? (not wishing to sound sarcastic or disagreeing - genuine curiosity that I have not understood something basic?_
It's Newton's Law of Cooling. The greater the difference between the temperatures of an object and the environment it's sitting in, the faster the rate of heat transfer.

In this case, the object is the condenser, and the environment is the water. The condenser is hot, and the water is cold. The colder the water, the faster the rate of heat transfer from the refrigerant to the water. Since the condenser is using the same amount of electricity to transfer more heat, the efficiency of the condenser goes up.

Since more heat has been removed from the condenser, there will be more subcooling. This reduces the temperature of the refrigerant at the evaporator, which also increases the rate of heat transfer. Since the fan is using the same amount of electricity to blow air across the evaporator, but more heat is being transferred to the refrigerant, the efficiency of the evaporator goes up.

Both the condenser side and the evaporator side becomes more efficient, so the whole heat pump becomes more efficient.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by levelride »

In short, yes. I live in Michigan and we almost bought the model you shared (ended up going geothermal and w/ a different model instead). Air-sourced heat pumps, in general, are viable for water heaters and HVAC in the Great Lakes region. I live in a city that's pushing towards carbon neutrality by 2030. Air-sourced heat pumps, including water heaters, are being installed all over town.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

Valuethinker wrote: Tue Sep 21, 2021 5:36 pm
talzara wrote: Mon Sep 20, 2021 5:59 pm Using attic air could even be counterproductive. The manufacturer specifies an ambient temperature range of 37 to 145°F. If your attic gets hotter than 145°F, the heat pump will shut off!
Is the saving anything more than marginal?

If you live in a winter climate the "waste" heat is simply a relatively expensive way to heat the house (electricity >> gas price).

If you live in a more southern climate then the additional heat added to the house (from the operation of the HP) is quite small, relative?
Probably not, but the OP is going to a lot of trouble to draw air from the attic. The whole point is to save energy.

If it ends up using more energy because it shuts off the heat pump, then why do it at all? Just leave it alone and draw air from the basement.
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Re: Hybrid Electric Pump Water Heater in Northern Climate?

Post by talzara »

brianH wrote: Tue Sep 21, 2021 7:23 pm
talzara wrote: Tue Sep 21, 2021 6:17 pm It's only a 4200 BTU/h heat pump. It doesn't need a big fan.
Yes, with no duct work, but you quoted the manual back at me implying that it would operate fine with 65' of ducting to an attic space. I highly, highly doubt that it would in the real world.
4200 BTU/h is only 70 BTUs per minute. It doesn't need a big fan, even if there are ducts.

Rheem has engineers to do the duct calculations and make sure they can supply enough air for the fan. If the engineers were really as bad at doing the calculations as you believe, then the fan on the heat pump is the last thing you should worry about.

Power-vented gas water heaters have small blower fans, and they're allowed to vent through the roof from the basement. Gas furnaces also have small inducer fans, and they're allowed to draw air from the attic, to the basement, venting through the roof. If they get those duct calculations wrong, then people will get poisoned by carbon monoxide.
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