Hot water heater bad backdraft

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vprgtsr001

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Currently have a 74 gallon hw heater. Noticed that our recently finished basement has been very hot and humid even w dehumidifier running (almost constantly). Walked into the mechanical room today and it was like a sauna. extremely hot and humid. the hw heater was running due to 2 people currently showering. putting my hand above vent hood i noticed a large amount of steamy air bypassing the vent all together. This, i assume, is why the mechanical room was so hot, and why the now insulated finished basement has been hotter and more humid.

we had the hw heater installed several years ago, and it was upgraded from a 50 to 74, the plumber upgraded the exhaust vent pipe at the same time to make it up to code in nj. The town came out and inspected as well. currently the exhaust pipe inside the hw heater is 5" but the vent pipe is only 4". I assume thats correct (to minimal standards at least) considering the plumber upgraded it and the town inspected it. But would it vent better if it was a 5" or 6" vent pipe?

Things definitely effecting backdraft and the negative pressure in the house currently are 2 portable AC units that vent outside, 2 100cfm+ bathroom fans, a range hood that's at least 350cfm. plus dryer. All of the above vent directly outside, and during the summer months many running at same time.

Going to call a plumber this week to come check it out and hopefully fix the problem. I was looking for some advice from this forum for proper fixes to make sure we don't get jerked around and so its done right.
 

vprgtsr001

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Your flue has a blockage in it
It’s clear. Had the vent pipe off crystal clear to chimney. Can see inside chimney at bottom it’s clear and clean. Threw a ladder up and looked down chimney. Also clear and clean put a hockey stick into vent and had someone move it around and i can see it perfectly down chimney.
 

vprgtsr001

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can you send picture of hwt vent...also is is room have proper fresh air makeup
i'll take a picture tomorrow. i had a plumber out since i last posted. he said all looked well w/ the plumbing. said we needed fresh air intake into house most likely. we did opt to have him upgrade the 4" vent pipe to a 5" pipe in hopes that, that would help with the venting but it unfortunately did not. i also cut in and installed a 6" round fresh air intake into the mechanical room. but with the insect screen on it, it impedes airflow and it doesn't seem to help either. we just got a brand new dryer as well which seems to have a more powerful blower motor. when the dryers running as well as the 2 portable ac units its causing quite the negative pressure issue in the house. i walked into the mechanical room today and it was blazing hot and steamy again. i felt the vent pipe and it was ice cold. all the combustion gases were coming into room. i ran upstairs and cracked a window in the kitchen which is between the dryer and 1 of the portable ac units. went back downstairs and immediately the down draft to hwh was gone and it was venting properly. the only problem is then on hot days if i have a window in the house open it defeats the purpose of the ac's and the house is gonna be hot. I was thinking about getting one of those inline duct fans and attaching it to the fresh air intake in the mechanical room directed inwards to actually PULL air into the mechanical room. might need to get an hvac guy out next.
 

fixitron

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The limiting factor on horizontal venting of Category I (natural draft) gas appliances is usually the 1 1/2 rule. The vent can go 1 1/2 feet times the diameter of the vent and then it has to be up-sized. The starting size is the diameter of the vent connector provided by the manufacturer, which is usually 3". Although not code, it is good practice to come straight off the draft hood with at least 12" of straight pipe before adding an elbow (same goes for bath fans).
So you have discovered that your house is fairly tight and now the water heater is competing with other exhaust fans, and they are winning. They are depressurizing the whole house, which will pull air down the flue of the water heater, even when the water heater is nor running! You have to provide air for combustion to the water heater. Running a pipe from the outside to near the water heater won't do it because it won't overcome the power of the exhaust fans in the house.
You could install a "Fan-in-a-Can" from Fields Controls which would turn on when the water heater turns on. I have seen tight houses where the appliance would still backdraft with that installed, because it could not overcome the effect of more exhaust "power" from other fans in the house.
The best solution is a sealed combustion water heater. If you have a lot of demand for hot water, or occasional need for a lot of hot water, then it should be a tankless water heater. You also need to consider that you may have a hard time finding a sealed combustion water heater larger than 50 gallons.
As for your comment about having to open a window defeats the purpose, that backdrafting brings a lot more hot air into the house than an open window, never mind the danger of high CO (Carbon Monoxide)! Make sure that you have current (not expired) CO alarms and be aware that they will never do off below 35 ppm or display anything less than about 25 ppm, so you could still feel a bit sick from CO and not know it.
 

RenewDave

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You need combustion air or “make up” air. That HWH is probably 74000 btu unit. You need a minimum of 50 cf per 1000 btu to have enough fresh air to have an adequate flame with correct exhaust. What is happening is that your HWH is pulling air down the flew to get air to burn. Very dangerous situation. I have seen fires because of this. And you should not be sleeping down there either. Co poisoning, “go to bed don’t wake up, ever”. You need a fresh air vent low maybe 14x14 and one high, 14x14 to get enough air. Please don’t play with this, it’s very dangerous.
 

FishScreener

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First get a CO alarm. You said you tried installing an outside air feed from the outside but the screen is retarding the flow. Could you put a fan on it?
 

Jamesplumbing06

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I bet you got a tiny pin hole in the stack of the tank. You mentioned moist air? Burnt gas is dry. Moisture is coming from somewhere and the center flue pipe is a hidden culprits. Do you have a way to make smoke? Or put a lighter up to hood while lit. Also you mentioned it’s going into an old chimney. Check that the heater flue is going upward the way to chimney.
If the air is moist then you got water coming from somewhere getting steamed. Or you could have massive amounts of condensation due to oversized flue. I am not a gas or vent specialist. Just grasping at straws. Good luck and god bless. Co2 detector is always needed. Please get a pro for this one. Gas and unknowing victims don’t match.
 

mike fiore

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I just had a customer with 40 gallon ao smith nat. gas tank that wasn't drafting properly. checked all usuall suspects with no luck. called ao smith tech support and they said they have had issue before and gave me a new tank under warranty. never seen this before. just thought of this thread and wanted to pass on info.
 

Nukedaddy

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It would be a good idea to check the top of the vent. Is it downwind and below the roof peak? Is it surrounded on 2 sides with roof or second story? Short “stub” stacks are notorious for poor draft. Outdoor vents that go from the appliance then straight out the wall, then up past the eaves are terrible, too. Especially if made of single wall pipe instead of type B double wall vent. The flue gas has to stay hotter than outside to draft.
Oh, and burning natural gas DOES produce water as a product of combustion. It is NOT dry..
 

Jamesplumbing06

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It’s vented into a chimney. So we assuming it’s up above roof peak.



It would be a good idea to check the top of the vent. Is it downwind and below the roof peak? Is it surrounded on 2 sides with roof or second story? Short “stub” stacks are notorious for poor draft. Outdoor vents that go from the appliance then straight out the wall, then up past the eaves are terrible, too. Especially if made of single wall pipe instead of type B double wall vent. The flue gas has to stay hotter than outside to draft.
Oh, and burning natural gas DOES produce water as a product of combustion. It is NOT dry..
suming
 

Jamesplumbing06

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Here you can tie into a chimney as long as it’s a proper chimney. If it has been closed off then I usually call a chimney sweep to inspect first but that chimney sweep has talked me into very easily running vent thru chimney and just using chimney as a chase. Also I wasn’t aware gas made the condensation. I gonna start putting a pan drain under my vent free gas logs. That I had to install a humidifier beside because our air dries out when the vent free logs are on. I always thought the instant heat going thru the colder pipe produced the condensation. Then once everything gets hot the condensation slows down enough for the hot MOIST (?) air to dry it up and make it dusty in combustion chamber. My bad. Either way check vent. I going to buy a dehumidifier before winter.
 

PattyD

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I bet you got a tiny pin hole in the stack of the tank. You mentioned moist air? Burnt gas is dry. Moisture is coming from somewhere and the center flue pipe is a hidden culprits. Do you have a way to make smoke? Or put a lighter up to hood while lit. Also you mentioned it’s going into an old chimney. Check that the heater flue is going upward the way to chimney.
If the air is moist then you got water coming from somewhere getting steamed. Or you could have massive amounts of condensation due to oversized flue. I am not a gas or vent specialist. Just grasping at straws. Good luck and god bless. Co2 detector is always needed. Please get a pro for this one. Gas and unknowing victims don’t match.
One of the byproducts of proper combustion of natural gas is water. The other is carbon dioxide.
I think the OP needs a draft insider for the existing heater or an upgrade to a power vent model.
 
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