using dampers to swap between winter/summer for heat pump water heater in garage
due to crazy high gas prices but cheap electricity — paying $ 70 a month to heat my water with nothing else on gas, i’d like a heat pump water heater.
my water heater is in the garage and i’d like to be able to have the intake on a damper so that i could switch between hot attic air in the winter, or hot garage air in the summer.
i have a ventilated attic and in the summer when its 105f outside, it is an unbearable temp up in the attic. from what i’ve read, there seems to be about a 20-25 degree temp drop between intake and exhaust. so dumping the exhaust into the garage would only make it hotter.
there is plenty of easy attic access above the garage, so i’d be able to place the intake/exhaust far from one another.
the attic will get decently warmer over ambient depending on the amount of overcast, but generally the winters here are 40-60 degrees. very very few days below freezing.
but i definitely don’t want to dump the cold air into the garage.
does any of this sound reasonable? theres plenty of manual or low voltage dampers available.. doesn’t seem overly difficult as far as ducting goes.
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In my experience HPWH's are intolerant of any obstruction on the air intake -- they shut off the compressor if the flow is restricted.
That said, I think the only way to know is to try. Do note that the normal thing to do is have the water heater take air from and return it to conditioned space. During cooling season it assists the air conditioning.
I would filter air before pulling it from either the garage or attic.
This is probably not a good idea per fire code. You are required to have a fire barrier between the garage and the living space, which is usually 5/8" drywall. That fire barrier has to include the attic space, which is either done on the garage ceiling or with a partition within the attic. You do NOT want to penetrate those fire barriers with a vent -- if you did, you'd have to use a fire rated damper in the vent. I see that kind of thing often in commerical buildings, which tend to have dampers large enough to crawl through, but I've never seen it done in a residential building.
I would just use the garage air in the normal way, and not try to get into the attic due to the fire barrier issues.
Bill
maybe im misunderstanding that, but the gas water heater in the garage already has several penetrations. one is a pipe leading out to the roof and 2 pipes are going into the attic to pull in air for combustion.
but im guessing that is not standard way to do things anymore. or maybe it never was. 🙂
cs55,
I don't know what he rules are around electric heat pumps, but here anyway, no gas appliances can draw or exhaust air from an attic.
wild. theres definitely 2 large open air pipes between the water tank closet going into the attic.
If the vents go THROUGH the attic and out through the roof to the outdoors, you're likely OK as long as the penetrations (where the vent pipe passes through the fire barrier) is properly sealed and fire stopped. You're permitted to "penetrate" a fire barrier as long as you seal up that penetration around the object, such as using fire stop caulk around a pipe, for example. What you CAN'T do is just cut a hole to allow air to circulate, or directly pull air from (or blow air into) one side of a fire barrier to the other.
As Malcolm mentioned, I'm also not aware of any codes that allow combustion appliances to draw or exhaust air from/to the attic. Heat pumps aren't combustion appliances, but I don't think they'd be permitted to exchange air with the attic, either, although it may be permissible to install the entire heat pump water heater IN the attic and just run plumbing and electrical lines to it.
Bill
https://imgur.com/a/7u1ck2p
thats how the current gas water heater is setup. the middle pipe goes to the roof, the other two are just open air.
:|
Why do you want to switch according to your statements the attic air is always warmer than the garage air?
Is there any chance of the garage getting below freezing?
If you use the HPWH to suck hot air from the attic the some of the air that replaces it is likely to be conditioned air from the gaps in your ceiling. You will likely increase the run time of that equipment.
How much of the $70 is the monthly connection fees?
If you are cooling your home most of the year is seems like putting the HPWH inside the home would be a better idea.
Walta
i would want to switch because i want to be able to cool the garage at least somewhat about 9 months out of the year.
in the summer; if i use attic air as the intake and exhaust it to the garage then it would actually just heat the garage because the attic air is too hot.
i would have the intake and exhaust decently far apart in the garage.
next to zero chance the garage will go below freezing in the winter
but im on a slab and theres literally nowhere a hot water tank could go inside the house :/
$35 service fee, $25 or so in taxes and other fees. like $5-10 worth of fuel.
If the water heater gives you a 20-25deg F air delta. Letting it recirc and cool garage air is probably the best. You may get better performance with hotter intake air (less lift) but there is likely a limit. Also I would only duct one side either intake or exhaust and be mindful of sizing and the effect of elbows, or you may run into airflow issues. Personally I would rather have it in the conditioned building envelope so it leaves a long clean life at moderate temperatures. Having it in a hot dirty (subjective) garage will likely lead to a shorter service life. My primary driver for location would be proximity to fixtures so you're not waiting for DHW delivery thru long pipes (assuming the adequate air volume /temp and noise concerns).
I'm presuming you're in a climate where the garage never freezes?
Just put the water heater in the garage, no ducting. In cold climates they're commonly put into basements that are probably colder in the winter than your garage.
it gets below freezing in general for maybe a few weeks in total where i live.
but i'm probably just overthinking this.
You might also consider a simple electric tank. Cheaper to install but more expensive to operate, they have lots of good use cases when low usage meets low electricity costs.
Why do you care if the water heater makes the garage 2° cooler in the summer? What it is 105 outside and it feels great going into the 103 garage?
Pipes in a slab seem like a problem until they fail and suddenly the plumber finds a clever way to put then in the attic, walls or a bulkhead.
Walta
the outside peaked at around 104 today, the garage peaked at 85.
unfortunately around 98% of houses built in the south are on a slab and have been for decades.