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Old 03-24-11, 09:36 AM   #1
Daox
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Default automatic water heater flue damper

As most of us know, conventional gas fired hot water heaters are very inefficient. Mine is rated at a whopping 55% efficiency, plus it uses a pilot light. And, as we've discussed in the past, pilot lights can use a fair amount of gas over a month (5-12 therms). So, a few people have opted to heat their water entirely with the pilot light alone. Unfortunately for me, this is not an option. My hydronic floor in my sunroom is run off of the hot water heater, and when that is running it can pull a fair amount of heat out of the tank. Enough to the point where I need to adjust the temperature up during the heating season to ensure there is hot water for showers.

So, is there a way to use the pilot light to heat as well as allow for the burner to run? That is my goal here. And, I think I have an idea to make a very simple damper that will keep the pilot light heat in, yet allow the burner to run without dumping CO into my basement. The idea is one or multiple super lightweight dampers. The damper would sit on the top of the water heater flue. It would be made up of only a piece of aluminum foil cut roughly to fit the flue diameter, and a support rod of some sort. In this case, I think a straightened paper clip would work. Being that it is so light, the hope is the hot flue gasses when the burner fires will be enough to lift the damper enough so that the exhaust can make its way up the exhaust flue. Here is an illustration of what I'm thinking of.




Now, some tweaking may be in order. Perhaps biasing the damper to one side so it naturally tips a little and makes it a little easier for the flue gasses to escape when the burner turns on. Also, if one large damper seems like too much to lift, perhaps two smaller dampers would work better?

Anyways, the idea would be to set this up with a carbon monoxide detector very close by and some manual testing to see if the flue gasses can in fact push the damper out of the way enough.

So, what do you guys think?

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Old 03-27-11, 12:40 AM   #2
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If it could be done safely it would likely yield you some great savings. Do you plan on letting the increased flow of exhaust open and close the damper?
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Old 03-27-11, 08:49 AM   #3
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55% efficient? I assume the remaining 45% includes heat escaping up the pipes and through the walls of the HWH, because 55% efficient combustion is hard to achieve.

I just tuft-tested my flue vent. Basement air is drawn into and up the flue with just the pilot light running. This is an instance of my HWH stealing heat from my house.
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Old 03-27-11, 11:57 AM   #4
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I was actually going to play around with this more today. Yes, the heater is rated at 55% efficiency. There is a turbulator inside the flue to enhance heat transfer. I am hoping the hot exhaust from the burner turning on will be enough to push the damper out of the way. Only testing will show.
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Old 03-27-11, 03:19 PM   #5
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Well, I did as I said and tested it out. The results were quite interesting. It was pretty much installed as its shown in the picture below, but I rotated it to fit in the little flue grooves. When the pilot light was on, it seemed to be fine. There was definitely a reduction of the amount of convection going on and heat escaping the flue. However, once the burner turned on, it actually picked up the damper and moved it. So, it needs to be tied down or something.


Here is the flue without anything over it.



Here is the flue with the damper.
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Last edited by Daox; 03-27-11 at 03:22 PM..
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Old 03-28-11, 08:29 AM   #6
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Very interesting.....I'll be watching with keen interest as I have a natural gas HWH. I thought my biggest concern was the open vent pipe sucking heat out of my house. Even so, if can cut down on wasted heat from the HWH, well, that saves money too. Keep up the good work.
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Old 04-02-11, 11:26 AM   #7
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Any updates on this yet .. I assume your still alive, everyone I have talked to say don't block or reduce flow at the flue at all the CO gass will kill you.
Please tell me you have a CO alarm nearby.
I however believe that theres room to play ..but how much is the question.
And then you also have to question whats your life worth.
I know that you can get a hot water tank that has electronic flue control, but thats also no standing pilot.
I am very interested in what your findings are.
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Old 04-02-11, 11:46 AM   #8
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Haha, still quite alive. I haven't yet put a CO alarm near by but that is definitely the plan if I ever get something close to working properly.
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Old 05-12-11, 11:47 AM   #9
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I'm interested in this little experiment also.

While by no means perfect: the house that we just moved in came with a cheepie 6-yr warranty A.O.Smith water tank (natural gas of course, thus the interest in this subject) that may have a few more years left (inner glass lined tank has a bit of rust water coming out even though I flush/drain from the bottom petcock every several weeks)...and I'm actively shopping for a better deal (still into storage hot water tank units as I don't want to do any cosmetic "damage" to the house by running PVC-based hoses for high-efficiency/condensing venting methods), not wife approved..

Budget is a concern at this moment but granted: I can find something that doesn't cost more than double (compared to typical 6-yr warranty heater tank), or close to an additional 60% to that of a standard 10yr warranty tank, then I'm all for it.

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Old 05-12-11, 01:04 PM   #10
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I haven't tinkered with it since the last post. I do think its viable, but would take work to get it working really relaibly.

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