Ducting for Hybrid Hot Water Heater

[dlu]

We're installing a Rheem Hybrid (heat pump & electric) hot water heater. The space where the heater goes is very tight and I need to use elbow on the cold air discharge as I come out of the heater. The discharge is 8" and this results in the elbow protruding about a foot from the heater -- I've only got about 10" so it's time to get creative!

The discharge ducting will be short, so I could step down to 6" or even 5" ducting, but I need to make the first turn right at the heater.

So, what I think I need is either a reducing elbow or a very short straight reducer. Does such a beast exist? Google is finding me all sorts of irrelevant suggestions...

 

[peter halle]

The instruction / installation manual does have instructions on ducting.  I have one of these in my garage.  Out of curiosity where are you installing this?  How are you dealing with the condensate?

Peter

 

[dlu]

The instruction / installation manual does have instructions on ducting.  I have one of these in my garage.  Out of curiosity where are you installing this?  How are you dealing with the condensate?

It's replacing an all-electric water heater in our bathroom. The old heater was completely boxed in -- literally no access -- so I'm making some changes, but didn't want to do a major overhaul of our plumbing. This means that I don't have a ton of room for the ducting. My plan is to exhaust the waste cold air into the attic -- I don't think this will make things worse in the winter and it may help some with A/C costs in the summer. I'd like to use the unit for cooling during the summer, but I'm not sure that there is a way, short of major ductwork, to get the cool air into the house. During the summer we'll draw the intake air from the attic, when it starts getting cold we can draw the intake air from the bathroom.

Since the bathroom is above grade, I was planning on plumbing the drain pan to a trap and then to the nearest gray water line. My plan is to put a tee just outside of the drain pan and run the condensate line to there -- my thought is that this way I'd end up with adequate capacity to deal with a significant water heater leak and not have to worry about the trap drying out due to the condensate flow.

The instructions have good information for designing the ducting system (in terms of lengths and losses) but they assume that you know what parts are available. Hence my question about reducing elbows 

 

[Cheese]

If you change the ducting to 6" immediately exiting the heater, you'll save about 2-1/4".

A 6" elbow is about 9.6" tall while an 8" elbow is about 11.8" tall. That's you're 2-1/4" that you need.

So, installing a 6" start collar on the heater and then going with a 6" elbow may get you what you need. [smile]

If you go this route, make sure you thoroughly seal the start collar with ALUMINUM duct tape...NOT cloth duct tape. Also, I'd Pop Rivet the start collar in 8 places rather than using screws.

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[smorgasbord]

We're installing a Rheem Hybrid (heat pump & electric) hot water heater. The space where the heater goes is very tight and I need to use elbow on the cold air discharge as I come out of the heater. The discharge is 8" and this results in the elbow protruding about a foot from the heater -- I've only got about 10" so it's time to get creative!

You should carefully read the installation manual - I installed a propane high efficiency water heater and the ducting requirements were quite stringent in terms of duct size and elbow radius, especially close to the water heater. Once I got about 2' away I could reduce and restrict according to a formula provided.

 

[todd_fuller]

Off topic, but I am considering a Rheem hybrid to replace two propane water heaters. On another forum, one user said that these were very loud in operation. I hadn’t heard that before. Did they just get a bad one or what? I expect it’s more like a fridge running than a vacuum.

 

[peter halle]

The Rheem does have a fan that is louder than a refrigerator.  It actually moves quite a bunch of air.  Mine is in the garage and you can hear it inside the house along an adjoining wall.  Mine has been installed two years now.  it does save a bunch of $$ in utility costs versus a conventional electric hot water heater.  In your situation you will have much worse recovery time - the heat pump mode is cheap but isn't rapid recovery.  Also if you a odd water need like I do (my hot water smells like rotten eggs at times) and need to change your anode to something different than the standard one be advised that the anode is basically permanently installed.  Rheem claims that it can be replaced but two professional companies plus my attempt have proven otherwise.  I can get around my water problem by running a quart of hydrogen peroxide thru the hot water heater every couple of months.

Think about the recovery time please.

Peter

 

[jeh]

Seems to take the simplest device and make it substantially more expensive and complicated. Two heating coils (or burner), two thermostats, a pressure release valve and a tank. In your case you lose the burner but pickup what I believe is a heat pump possibly requiring a new circuit (More likely coming from propane).

I feel your pain on the propane, but why not get  an commercial electric water heater. Probably close to the same cost but way simpler. You can get high capacity ones. I picked up spare 105 gallon as a backup for when they no longer can be sold which is coming soon. My spare is a residential Marathon model and it is leak proof. Stainless steel tank, surrounded by 2-3 inches foam enclosed in a nylon-ish case. If my electric truck coop did not have one left I would have bought a commercial one to be ready for when the day comes.

 

[dlu]

Off topic, but I am considering a Rheem hybrid to replace two propane water heaters. On another forum, one user said that these were very loud in operation. I hadn’t heard that before. Did they just get a bad one or what? I expect it’s more like a fridge running than a vacuum.

The new (Gen 5) ones are noisier than the previous iteration (and so, far also more reliable -- the noise is akin to a loud fridge. Nothing like a vacuum. If you duct the heater, especially the exhaust, that really helps with the noise.

 

[dlu]

Think about the recovery time please.

Our solution to the recovery time issue was to get a bigger water heater. It works, but I'm not sure it was worth the hassle with the extra space it takes up. If you run the heater in "energy saver" mode the heater's "smarts" attempts to balance efficiency with demand. There is also a high-demand mode that runs both the resistance heaters and the heat pump -- that's expensive but the recovery is quite fast.

The Rheem EcoNet app can schedule the heater's mode, so you could, for example have it automatically put itself into high-demand mode at bath time. You can also do that manually from the app or the control panel on the heater.

 

[Michael Kellough]

The above post is in the pattern of the typical BOT that posts here and this BOT’s previous post, although shorter than usual.

1 Commiseration
2 “Personal” experience
3 Solution consisting of regurgitated material from earlier posts

 

[Ron B]

What is the purpose of these "BOTs".  What are they trying to achieve on FOG?

 

[ariellewilliams]

You could try adding a 6" start collar on the unit and then using a 6" elbow; that’ll likely get you the clearance you need.
Just make sure to seal everything up good with aluminum tape, not the regular cloth stuff. I also riveted mine in a few spots to keep it solid, but screws would work if that’s what you’ve got. And yeah, if you’re in plumbing in Las Vegas, might be worth having someone with experience check it out too, just in case you run into more duct or venting quirks with the hybrid setup.

 

[Mini Me]

I am curious, why does a heat pump HWS need to be ducted at all?

 

[squall_line]

I am curious, why does a heat pump HWS need to be ducted at all?

Since most heat pump hot water systems have the pump mounted to the tank, the ducting would help keep from freezing out the room in which it's installed, especially if it's in a tightly enclosed space.

 

[Mini Me]

I am curious, why does a heat pump HWS need to be ducted at all?

Since most heat pump hot water systems have the pump mounted to the tank, the ducting would help keep from freezing out the room in which it's installed, especially if it's in a tightly enclosed space.

I am still curious because we don't have cold climate problems you guys have. If a duct is installed a fan will be needed?? to extract the air but possibly not. To extract the air make up air from outside the room has to enter from somewhere or the duct would not work and if that make up air is from outside where the air is cold the air in the room will drop anyway. I have been using heat pump HWS's for nearly 40 years and they have always been outside but 10 degrees C is cold where I live and I can undestand the need to have the HWS inside.