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Question DetailsAsked on 3/8/2015

Hybrid Heat Pump Water Heater installation location? attic? closet?

This is for new construction residential later this year. Where the home is big enough that I'll probably need 2 water heaters. One of them will probably be in the garage with the other near the bedrooms. Back by the bedrooms; options seem to be in the attic or maybe in a closet on the side of the house.

I'm assuming the attic would be fine for airflow but I'm concerned the weight and having that much water above living space. Are these installed in attics very frequently and is that problematic?

If I had a "closet" that could fit the water heater with a duct/connection to the attic for airflow would that be acceptable? Or would I need active airflow(fan) to pull the cold air up into the attic?

Any advice is appreciated.

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3 Answers


The attic trusses can be engineered to support the weight,extra cost of course.

Fan that comes in the unit can't be ducted to the attic. If you use a separate fan, it will be pulling "conditioned air" from the home, this would negate any savings from the Heat Pump water heater,maybe more.


Answered 5 years ago by BayAreaAC


As BayAreaAC said, the fan in the unit just pulls ambient air into the unit for the heat pump to "extract" the energy out of it to heat the water - it cannot pull from or route the air elsewhere, it is not powerful enough.

The issue of water heater above the rest of the house is a legitimate concern - I could never understand putting boilers or water heaters anywhere but in dedicated utility closets on the outside of the house (in warmer climates) or on the lowest floor in the house - whcih is usually the garage.

Support is an issue - usually it is overcome by putting the unit on a platform straddling several joists (or truss bottom chords) where they are supported on an underlying wall. THis of course makes that a load-bearing wall,which it may or may not be designed for - many installers forget that minor fact, which can cause long-term floor joist sag issues.

The way the heat pump in the hybrid heater works is it extracts heat from the surrounding air to heat the water, then exhausts that air (now chilled below ambient temperature) back to the ambient area. So, it cannot be installed in a "closet" without good fresh air inflow or it rapidly loses its heat source. if it is installed in a conditioned space there are several drawbacks - while in the summer it removes heat and cools the ambient area to a limited extent, in winter it is pulling heat out of your air - basically stealing it from the furnace, which then replaces the heat with say a 60-90% efficiency. This can be a major lose-lose proposition with electric heat. With gas furnace but electric water heater (an unusual combination) depending on gas furnace/boiler efficiency this can be a negative or not, depending on furnace efficiency and gas costs versus electric. The most efficient operation is if it is pulling hot air from outside or is located near a furnace or boiler that is generating "excess" waste heat in the area it is located in, so stealing some of that heat is a benefit.

Attic location can make sense in the summer when the attic is hot so the water heater has an ample source of heat, and the cooled air reduces the heat in the attic - sounds like a win-win,right ? However, assuming you have cold winters and an unheated attic, in the winter the attic can easily get so cold (below 35-45 degree cutoff for most brands) that it can no longer extract heat from the air, so it is then acting as a straight electric water heater trying to keep the water hot in a cold environment - not an energy efficient solution., and not much better than an outdoors utility closet - with the attendant additional risk of freezing pipes up quickly if the power fails, and eventually freezing the tank itself.

I have seen new house plans with a seasonal variation - installation in a separate utility closet on an outer wall or right inside an outside wall with low-resistance large-diameter fresh air ducting and insulated enclosure and doors, so it draws outside air for its heat in the warm season and exhausts the cooled air into the house, and in the winter is rerouted so it uses indoor air and exhausts to the outside, but this is a new design feature not in common use, and some building departments would have an issue with it because the fan is so weak you might get reverse flow due to the differential air pressures between the house and outside.

There is at least one brand out there now with an optional stronger fan that allows for up to 8-10 feet of ducting on both the inlet and outlet side, to accomodate this sort of ducting. Properly done, with proper automatic controls to reroute the airflow (similar to what a heat pump does with its refrigerant reversing valve in changing from A/C to heating mode) this does have a significant potential to overcome the inherent problems with a heat pump operating inside a building HVAC envelope.

There are also hybrid gas water heaters out there that avoid some of the energy cost issues with electric heaters - but you have to really be into crunching numbers to be able to figure out whether a hybrid heater of either type is actually going to save you money or not - and if it is going to be significant enough for the duration you expect to live in the hosue to have it make sense for you. That is one of the big flaws in many energy conservation programs and ads - they look at the overall big picture from a "house" efficiency standpoint, but ignore the fact you may be moving typically every 5-6 years so you may not be interested in installing a higher efficiency unit or a thousand or two more for a few hundred $ a year in energy savings which will mostly benefit future homeowners who may pay little or any more for that higher efficiency when they buy your house.

Of course - the downside is commonly substantially higher cost for limited annual energy savings unless you have inordinately high energy costs and no access to cheap gas.

Here is another recent discussion on hybrid water heater FYI -

Answered 5 years ago by LCD


Warm climate: in the garage

Cold climate: in the basement (and it will dry the air)

Answered 3 years ago by albator

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