Melted grommets

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Old 07-08-20, 12:29 PM
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Melted grommets

I installed a 40 gallon Richmond Water Heater in November 2019. Everything was fine until I discovered two melted grommets (see attached) at both the cold water inlet as well as hot water outlet. Does anyone have an idea why this happened & why 7 months later?

 
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Old 07-08-20, 12:51 PM
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The heat from the exhaust is what melted them. I don't know enough about gas water heaters to know what the fix would be.
 
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Old 07-08-20, 02:23 PM
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I am also not gas water heater pro.
The only thing I can think of is that there is a restriction in your chimney and hood.
Normally the hot gasses go up the chimney and also pull some room air up into the hood.
It looks to me that for some reason this is not happening so that area is overheating.

I cannot see but is it possible that there is no open space between the water heater chimney and the house chimney so that no room air can enter the hood and go up the chimney?
 
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Old 07-08-20, 02:52 PM
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I have a gas heater in my home and a good number in my rental properties. I have never had the plastic trim rings melt like that. The exhaust gasses are not going up the flue like they should. Do you have a carbon monoxide detector? If not I would get several. Put one in the room with the heater and another in your bedroom just to be safe.

I would inspect the whole exhaust flue if possible to make sure there is nothing clogging or blocking it. Also inspect the cap on the roof. It prevents downdrafts from blowing the hot exhaust gasses out the bottom and keeps animals and debris out.

Have you done any renovations that would have restricted airflow to the room where the heater is located? You need to insure there is a good, free airflow into and up the flue.
 
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Old 07-08-20, 04:33 PM
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... restricted airflow to the room where the heater is located? ...
You mean fresh airflow into the room, known as makeup air and also necessary ...

Nowadays it is common to have a vent in the wall to the outside near the heater. Decades ago, buildings were not that well sealed against outside air leaking in and a wall vent was not provided if the square footage was great enough and there were enough doors and windows.

There is suipposed to be a gap under the little hood, between the end of the flue pipe coming out of the water heater and the flue pipe continuing up to the discharge to the outside. This gap is intended to reduce the effects of pressure changes in the flue due to wind, and resulting combustion problems down below. An unfortunate and unavoidable side effect is that on average some additional room air not used for combustion oxygen will go under the hood and accompany the exhaust gases up the flue.
 

Last edited by AllanJ; 07-08-20 at 04:55 PM.
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Old 07-08-20, 05:41 PM
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The inlet and outlet pipes look awfully close to the vent to me. Without going down to check mine I'd say they are closer to the vent than on most gas water heaters.
 
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Old 07-09-20, 06:33 AM
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An occasional burst of exhaust gases out from under the hood atop the water heater cannot be ruled out but should be short, few, and far between. Go thorugh the preceding replies and see that the problems mentioned are corrected, and that should prevent melting of the grommets.
 
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Old 07-09-20, 01:24 PM
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Was there any warranty regarding the installation? You might get the installer to fix it if there is something he didn't do correctly installing the flue .... but it the flue got plugged/restricted after the fact - that would be on you.
 
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Old 07-09-20, 07:25 PM
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He said he installed it.
I think he messed it up re: has blocked the hood so it does not let in any auxiliary/room air into the chimney.
I am not a pro at this but I would think this could be a dangerous situation.
Unfortunately he has not posted any updates.
 
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Old 07-09-20, 09:52 PM
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Melted grommets

At the time of the installation, the entire vent pipe, all the way down to the draft hood was without obstruction. My wife stood in the empty utility room & I went on the roof & dropped a golf ball down the pipe & it fell to the floor. The previous water heater was also a 40 gallon Richmond, with virtually the same specs. The only thing changed was the draft hood, whose dimensions were identical to the old draft hood.
I've placed a carbon monoxide detector in the utility room, which contains the water heater; it reads normally & hasn't alarmed. I've worked at the hospital every day since discovering the melted grommets. I've checked the straight run of PVC from the roof down & no obstruction exists. On Friday, I'll disassemble the vent pipe which connects to the draft hood, in search of some type of obstruction.
 
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Old 07-10-20, 03:48 AM
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Is there a gas furnace or air handler in the same room? I've seen this condition once before, and attributed it to negative pressure in the room created by a poorly-sealed (as in not sealed at all) return duct to the adjacent gas furnace.
 
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Old 07-15-20, 11:14 AM
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Melted grommets

I removed a section of the water heater's vent pipe at the draft hood as well as the vent cap on the roof; the vent pipe was clear with no obstruction whatsoever.

(Disregard this statement from my post of 7-9-20 at 11:52 PM: "I've checked the straight run of PVC from the roof down & no obstruction exists." That was from a previous AC repair.

My old Richmond Water Heater didn't have the grommets/plastic trim rings. Perhaps, this has been a preexisting issue, discovered only because of the grommets/plastic trim rings on the new one, or a design flaw that casualjoe alluded to: "The inlet and outlet pipes look awfully close to the vent to me."

If preexisting, why did it take 7 months to occur?

 
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Old 07-15-20, 11:20 AM
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The pipes may look close but that is how the manufacture built it so that is not going to be the problem.

If there is no blockage then there is a draft problem. That leaves the room to tight and not getting enough fresh air or the possibly the vent on the roof is not high enough above the roof.
 
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Old 07-15-20, 12:00 PM
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Is the water heater in a closet? Usually when they are in a closet the door is either louvered or has a grille cut into the door.
 
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Old 07-16-20, 08:03 AM
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Melted grommets

Yes, the water heater is in a closet, but the door is neither louvered, nor does it have a grille cut into it. The flooring, 12" in front of the water heater, has a vent (14" x 6") cut into it, which vents to a crawl space under the house. We tested for backdraft with the closet door opened as well as closed & waiting an appropriate amount of time after increasing the water heater thermostat's temperature; no backdraft.

What we did discover, after doing doing some Internet research, is that an exhaust fan, & in this case, our whole house fan, can cause a water heater backdraft. By the way, our water heater is the only major appliance connected to this vent pipe. As an experiment, we opened the windows the same amount we do when running the whole house fan, increased the water heater thermostat's temperature, & waited an appropriate amount of time after increasing the temperature. Then we turned on the whole house fan. Sure enough, warm-hot air was blowing from the draft hood area with the closet door open. I didn't check with the door closed, but several nights ago, the outside temperature was cool enough & we turned on the whole house fan two consecutive nights; the first time since having installed the water heater (7 months ago). Showers were taken after turning on the whole house fan, partially emptying the water heater & causing it to cycle as it did during our experiment. Following that second night is when I discovered the melted grommets.

Based on the room parameters I mentioned (vent cut into the floor, etc.), is there a way to prevent this backdraft when turning on the whole house fan? Otherwise, every time we turn on the whole house fan, we're creating an unsafe condition, correct?
 
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Old 07-16-20, 08:17 AM
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Definitely unsafe! You might try weatherstripping the closet door to see if that helps. Another option might be to provide a supply fan to slightly pressurize the home when the whole house fan runs; not sure how practical that is.
 
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Old 07-16-20, 09:06 AM
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You need to isolate the closet from the negative pressure created in the house by the fan. How does fresh air from outside (not from the house) get into the crawl space? The effective area of those openings need to be at least as much as if not more than the area of the floor vent into the closet. Even better would be to run a duct from the outside through the crawl space into the closet and seal the door as was suggested since you may not know how much negative pressure is caused in the crawl space by the fan. Check the heater manufacturer's specs to know how much free area for input air is needed for the heater and size the duct and vents accordingly..
 
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Old 07-16-20, 11:32 AM
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The pipes may look close but that is how the manufacture built it so that is not going to be the problem.
I checked the spacing of the piping on my unit that I was comparing in my mind to the OP's unit. I believe the spacing is the same. When checking I also noticed a very slight distortion of plastic grommets on my Bradford White unit too. Not nearly as bad as the OP has, just very slight distortion from heat, but not enough to worry about. When I think about this issue it just reminds me of everything I have read about not connecting pex pipe directly to a gas water heater because of excessive heat from the vent.
 
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Old 08-04-20, 07:48 AM
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Melted grommets

After reading all the comments, I'm a bit confused as to which result is desirable. In one post, it's stated that some doors are louvered & in another, it's stated to weatherstrip/seal the door.

I tried a recent experiment with the whole house fan on, which is causing the backdraft. I stood in the closet with the door closed & there is absolutely no infiltration of air flow coming up from the floor vent. Then, I opened the door & air came rushing up from the floor vent. Which of these results are desirable?

Taking into account the post by by 2john02458 (Even better would be to run a duct from the outside through the crawl space into the closet and seal the door as was suggested since you may not know how much negative pressure is caused in the crawl space by the fan), how does this help neutralize the negative pressure created by the whole house fan? Please see the attached manufacturer's "combustion & ventilation air" requirements.

 
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Old 08-04-20, 08:43 AM
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Using the terms in the instructions that you posted:

If there was no door or if the heater was in an open room it would be an "unconfined space." The required air is drawn from the air in the house. However the house fan would still be drawing air back through the flue.

Using a louver door or high and low vents to the house would make it a "confined space." The required air is drawn from the house and/or crawl space by gravity (in the absence of a negative pressure, i.e. house fan off.) The house fan would still be drawing air back through the flue when on.

Sealing the door and closing crawl space vent to isolate the space from house air would make it a "confined space" that would need separate ducted venting for air. Since the space would be sealed off from the house air (with the door closed) little or no air could be drawn through the flue by the house fan. With the door open it could.

opened the door & air came rushing up from the floor vent
This indicates that the negative pressure caused by the house fan is definitely pulling air through the crawl space and the closet. If you check the draft at the hood on top of the heater in that same condition you would probably see a backdraft there as well. (A lit match or candle held near the hood opening will show the flame pulled away from the hood.)

What you need to do is isolate the closet from the effect of the negative pressure. Sealing the door would apparently do that since

with the door closed & there is absolutely no infiltration of air flow coming up from the floor vent
but you should check the hood for backdraft then as well. There may be some due to air being pulled in around the door. If there is no backdraft in this condition (door closed, house fan on, no air being drawn through floor vent) then the problem is solved. Put a door closer on the door to ensure that the door is not left open.

If there is still a backdraft once the closet is isolated (with the floor vent closed) it then needs its own supply of air ducted from outside as stated in the instructions.

how does this help neutralize the negative pressure created by the whole house fan?
It does not neutralize the negative pressure. It isolates the closet from the effect of the negative pressure. If air from outside cannot go through the closet (via floor vent or heater flue) it will come from other sources in the house such as stove hood, bathroom exhaust, cracks and crevices around windows and doors, etc. Obviously opening windows and doors will reduce the negative pressure created by the house fan but until enough area is opened to supply all the air needed by the house fan then the potential for backdraft through all the other vents and flues is still there.
 
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