Heat pump water heater ducting question?

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torpesco

New Member
Jan 7, 2022
15
BC
I have the Rheem and it is whisper quiet. I can barely hear it running and have to stand right next to it.
Wow... this makes me wonder if something is wrong with mine (Rheem installed in March 2021). I just used an app on my iPhone, so probably not as good as a proper meter, but above the unit it measures 75dB. Near the outlet, 67dB. 3ft away, 65dB. If I close the bifold door in front, then at 3ft away it's 52dB. The app says "quiet home" for 52dB... but it certainly doesn't feel quiet to me. Maybe it's partly the frequencies that make it seem worse. When the compressor is off, the room is more like 30dB.

Mine sounds more like mellow's AO Smith, I think. If not worse.

Edit: A google search led me to a couple posts of people commenting on the current generation being loud. One person described it sounding like "an industrial ice maker at a cheap motel." Seems about right.
 
Last edited:

torpesco

New Member
Jan 7, 2022
15
BC
Well following up on this two years later…. Maybe only one since I installed the ducting. The room is no longer a bedroom it’s a library with an open door way connected to the rest of the basement. Mechanical room is now closed off by louvered bifold doors.

The reason is it it completely vented indoors. With the ducting kit and 2 adjustable elbows an some flex duct, the intake draws air from above the the bifold doors from the library through an extra filter (and a bit from the suspended ceiling space). The exhaust elbow points down to the floor. This arrangement keeps the air very stratified. Hot moist air up too cold dry air down low.

I've been considering ducting for my HPWH because it's in a somewhat inappropriate space... so I wonder what you & others here might think of this wacko idea.

It's in a tiny little utility closet in the centre of my main floor that barely fits it and the air handler for the ducted heat pump we replaced our furnace with. I was left feeling like the sales guy wasn't interested in selling us the right system for our application. (Proper air volume, proximity of noise to living area.)

To deal with the tiny room getting very cold and probably operating inefficiently, I removed a piece of sheet metal that was screwed over a hole that duct cleaners punched in the air return for the heat pump (top right in the photo). Its fan runs at a low speed continuously, so the cool air from the water heater mixes into the air in the whole house. Seems ok. The house is comfortable. What I don't like is that the gap under the utility closet doors now functions as an air return.

I was wondering how crazy it'd be to connect the HPWH to that air return duct on both intake and outlet.

Now that I'm actually writing that out, I can think of a some possible negatives:
  • If I just connect both ends to the air return duct, it'll create a loop (say if the air heat pump is off)
  • If I split that loop, then air will be continuously moving through the HPWH and its filter will become a pre-filter for the air heat pump. The pipe diameter would be smaller, too, so it couldn't be a full split.
  • There may not even be enough clearance by the outlet -- there's just 4.5" between it and the air handler.
Now I partly wonder if I should add an intake vent above the doors like Evan, with the cool air just making its way out under the doors... but what I don't like about that is the thought of dumping cool air onto any area of our concrete floor in cooler months. The semi-adjacent kitchen is bad enough already. I also don't like the idea of the visuals of a vent like that in our family room. :-\

IMG_1504.jpeg
 

EbS-P

Minister of Fire
Jan 19, 2019
2,419
SE North Carolina
I've been considering ducting for my HPWH because it's in a somewhat inappropriate space... so I wonder what you & others here might think of this wacko idea.

It's in a tiny little utility closet in the centre of my main floor that barely fits it and the air handler for the ducted heat pump we replaced our furnace with. I was left feeling like the sales guy wasn't interested in selling us the right system for our application. (Proper air volume, proximity of noise to living area.)

To deal with the tiny room getting very cold and probably operating inefficiently, I removed a piece of sheet metal that was screwed over a hole that duct cleaners punched in the air return for the heat pump (top right in the photo). Its fan runs at a low speed continuously, so the cool air from the water heater mixes into the air in the whole house. Seems ok. The house is comfortable. What I don't like is that the gap under the utility closet doors now functions as an air return.

I was wondering how crazy it'd be to connect the HPWH to that air return duct on both intake and outlet.

Now that I'm actually writing that out, I can think of a some possible negatives:
  • If I just connect both ends to the air return duct, it'll create a loop (say if the air heat pump is off)
  • If I split that loop, then air will be continuously moving through the HPWH and its filter will become a pre-filter for the air heat pump. The pipe diameter would be smaller, too, so it couldn't be a full split.
  • There may not even be enough clearance by the outlet -- there's just 4.5" between it and the air handler.
Now I partly wonder if I should add an intake vent above the doors like Evan, with the cool air just making its way out under the doors... but what I don't like about that is the thought of dumping cool air onto any area of our concrete floor in cooler months. The semi-adjacent kitchen is bad enough already. I also don't like the idea of the visuals of a vent like that in our family room. :-\
You I think you need the ducting kit. The air return is now unfiltered with that hole. At least tape a washable window ac filter over it. Could you do what I did and put an 8” air intake above the closet door? Doesn’t have to be ducted if you duct the exhaust to the air return. Ie is there a header for that door? I have a washable filter on mine. If I were you I would.

Do you even have room to add the ducting kit for the HPWH, or will you have to make your own?

It’s a tough space but you have the air return. I say use it for the exhaust. If you do duct it you will need need to clean the filter much more often. I have a filter on my intake above the closet doors and the mesh screen that the units uses. If you did add a vent over the doors you could work to better sound seal and insulate the doors. Then make/buy a duct silencer for that it might not even need to be attached to the unit. Just An air return for the room.

My thoughts were these. Take the warmest air up by the ceiling in and dump it out on the floor would give me the best efficiency.

For you I don’t know if the intake even needs ducted if the exhaust is.

If you are running the hvac fan 100% of the time that seems unnecessary. Does your thermostat have a circulate setting where it might cycle? Mine does.

The most uncomfortable the library room gets is in the winter when the incoming water temp drops and the HPWH runs more. I like the cold room in the summer. It would be unbearable in the winter when we are running the wood stove and the heatpump is off. Think like 57-60 degrees.

Man that space is tight. Good luck.
 

torpesco

New Member
Jan 7, 2022
15
BC
Wow... this makes me wonder if something is wrong with mine (Rheem installed in March 2021).
...
Edit: A google search led me to a couple posts of people commenting on the current generation being loud. One person described it sounding like "an industrial ice maker at a cheap motel." Seems about right.
Read the rest of the comments on a Green Building Advisor thread on it and it sounds like units built in Feb 2022 or later are quieter. I'll have to look into a warranty replacement.
 

torpesco

New Member
Jan 7, 2022
15
BC
You I think you need the ducting kit. The air return is now unfiltered with that hole. At least tape a washable window ac filter over it. Could you do what I did and put an 8” air intake above the closet door? Doesn’t have to be ducted if you duct the exhaust to the air return. Ie is there a header for that door? I have a washable filter on mine. If I were you I would.
The filter is right at the top of the unit, where the return connects to it. (It's technically installed upside down -- our ducts exit at the bottom, under the slab foundation.)

Do you even have room to add the ducting kit for the HPWH, or will you have to make your own?
I'm not very optimistic about the kit fitting. It'd be nice to get more dimensions than Rheem has on their website.

It’s a tough space but you have the air return. I say use it for the exhaust. If you do duct it you will need need to clean the filter much more often. I have a filter on my intake above the closet doors and the mesh screen that the units uses. If you did add a vent over the doors you could work to better sound seal and insulate the doors. Then make/buy a duct silencer for that it might not even need to be attached to the unit. Just An air return for the room.
That sounds pretty reasonable. Yeah, I'd probably add a 2nd filter for the intake if I ducted the exhaust.

My thoughts were these. Take the warmest air up by the ceiling in and dump it out on the floor would give me the best efficiency.

For you I don’t know if the intake even needs ducted if the exhaust is.
Probably not, yeah. The main reason I can think of would be for noise, but if I'm lucky and get a newer, quieter replacement, maybe that will be less of a concern.

If you are running the hvac fan 100% of the time that seems unnecessary. Does your thermostat have a circulate setting where it might cycle? Mine does.
It's the way the system is designed. There is no 'off' option other than to turn the system off completely. Variable speed fan and variable speed compressor. I guess the theory is that running the fan on the lowest speed continuously keeps the temperature a bit more uniform and comfortable? Seems to work well.

Actually, one neat thing is when I use our fireplace (zero clearance, wood), the house warms up higher than the thermostat is set, the compressor doesn't kick in, and the temperature stays pretty even - (though warmer in the room with the fireplace, of course).

The most uncomfortable the library room gets is in the winter when the incoming water temp drops and the HPWH runs more. I like the cold room in the summer. It would be unbearable in the winter when we are running the wood stove and the heatpump is off. Think like 57-60 degrees.

Man that space is tight. Good luck.
Hah. Thanks. Seems like I may end up trying to make my own duct fitting for the exhaust. :(
 
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schweigert85

New Member
May 20, 2022
2
Honolulu
Heres my novel experience with my heat pump water heater so far touching all the topics covered in this thread -

I just got an AO smith 80 hybrid couple weeks ago and installed it in a small 4x10x8 utility closet - with the intention of ducting the exhaust to the larger "laundry room" its connected to - as I live in a year round warm climate, and and to take advantage of the cool exhaust air - as well as getting that cold air out of the closet to improve the tank and warm water pipes efficiency. I'm also running the condensate line through the wall and raining into a wash basin that my washing machine also drains into.

I installed it on a tile floor, on a pizza pie layout of bricks so its off the ground - did not use a drain pain.

I used the water heater for a week with the door to the closet door off just to make sure everything works before i drill holes into it for the vent kit, and also running the exhaust vents through the drywall to the laundry room.

NOISE -
Its not quite when you're next to it with the heat pump going... sounds exactly like the youtube video posted (I read its a fan rattle) - I've called AO smith for replacement fan and motor (which is the reason I went with AO smith as they have the best customer service) and they're sending the parts our immediately. with the door open, it echoes around the house about 30 feet away or so.

With the door closed, you cant really hear it at ALL - so drywall on stud (no insulation) seems to be enough to muffle the noise.

When its in a small room, they say you can run a louvered door, or duct kit. I think obviously the best is to use a duct kit - that way the noise stays in the room, and you get the cool air away from your warm stuff - i just wish they specified how MUCH of a louvered door they need.


DUCTING
My current configuration - is I installed two different 8" registers/vents in the drywall from the closet its in to the larger room - with the intention of one being for intake, and one for exhaust - however as I thought about it you dont really need to run duct for the intake, as it will be sucking in air through that vent anyway. I connected the exhaust and ducting to the other vent, and its pumping cold air out into the other room.

Heres the problem with venting the cold air away into another room - now you have a "warm" air space, and a heat pump pushing "cold" air through the ducting out of it. That means MAJOR condensation - all around the exhaust of the water heater, and on the ducting leading out - just like a a cold glass of water on a hot day - and all this condensation is on the exterior of the unit now. It... might be harmless... but it doesn't seem right.


I might try to swap my venting to the exterior room so that instead - its pulling the air directly from the exterior room, and instead the exhaust can escape from the other "unducted" vent - not as ideal, as then that closet would be cooled down instead, but probably preferable to all the condensation
 

EbS-P

Minister of Fire
Jan 19, 2019
2,419
SE North Carolina
Heres my novel experience with my heat pump water heater so far touching all the topics covered in this thread -

I just got an AO smith 80 hybrid couple weeks ago and installed it in a small 4x10x8 utility closet - with the intention of ducting the exhaust to the larger "laundry room" its connected to - as I live in a year round warm climate, and and to take advantage of the cool exhaust air - as well as getting that cold air out of the closet to improve the tank and warm water pipes efficiency. I'm also running the condensate line through the wall and raining into a wash basin that my washing machine also drains into.

I installed it on a tile floor, on a pizza pie layout of bricks so its off the ground - did not use a drain pain.

I used the water heater for a week with the door to the closet door off just to make sure everything works before i drill holes into it for the vent kit, and also running the exhaust vents through the drywall to the laundry room.

NOISE -
Its not quite when you're next to it with the heat pump going... sounds exactly like the youtube video posted (I read its a fan rattle) - I've called AO smith for replacement fan and motor (which is the reason I went with AO smith as they have the best customer service) and they're sending the parts our immediately. with the door open, it echoes around the house about 30 feet away or so.

With the door closed, you cant really hear it at ALL - so drywall on stud (no insulation) seems to be enough to muffle the noise.

When its in a small room, they say you can run a louvered door, or duct kit. I think obviously the best is to use a duct kit - that way the noise stays in the room, and you get the cool air away from your warm stuff - i just wish they specified how MUCH of a louvered door they need.


DUCTING
My current configuration - is I installed two different 8" registers/vents in the drywall from the closet its in to the larger room - with the intention of one being for intake, and one for exhaust - however as I thought about it you dont really need to run duct for the intake, as it will be sucking in air through that vent anyway. I connected the exhaust and ducting to the other vent, and its pumping cold air out into the other room.

Heres the problem with venting the cold air away into another room - now you have a "warm" air space, and a heat pump pushing "cold" air through the ducting out of it. That means MAJOR condensation - all around the exhaust of the water heater, and on the ducting leading out - just like a a cold glass of water on a hot day - and all this condensation is on the exterior of the unit now. It... might be harmless... but it doesn't seem right.


I might try to swap my venting to the exterior room so that instead - its pulling the air directly from the exterior room, and instead the exhaust can escape from the other "unducted" vent - not as ideal, as then that closet would be cooled down instead, but probably preferable to all the condensation
I get the condensation on the unit and my exhaust short duct elbow too. It has never dropped off though. It will probably condense on the unit no matter what you do.

I have considered insulating with bubble wrap or the foil faced bubble wrap. Cut everything to fit. Spray on some adhesive. Stick it all up. Haven’t done it yet.

Just my thoughts.
 
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