Any HVAC guys that can help?

RobMcBee

RobMcBee

Slow n easy when you're not gettin greasy....
Joined
Jan 12, 2009
Location
Fort Mill / Indian Land SC
This morning I noticed what smelled like natural gas exhaust coming from the room where my hot water heater is. Checked it out and found that Im getting a backdraft through my flue. It does vent, but b/c of the cold weather the first 30 seconds or so of running it has to warm the air to draft. This puts some exhaust into the house. Once it gets warm it drafts fine. My question is, should I create a fresh air supply like pictured below and seal the room/closet? Or does someone have a better solution? Also the flue pipe runs straight up and is a dedicated line for the water heater.

awww.nachi.org_forum_attachments_f20_25130d1226374323_combustion_air_0735.jpg



I didnt have this problem last year, so Im thinking sealing the crawlspace may have contributed to the problem. Im also getting a backdraft through my kitchen exhaust fan that I never had before, but Im going to install a damper there.


Thanks in advance!
Rob
 
For a draft to happen, replacement air has to come from somewhere. Ideally the replacement air originates from a different area from the exhaust. Otherwise you pull in exhaust and smell. If your house is too tight, no draft. This is why people with woodstoves and fireplaces sometimes report that the smoke smell they have goes away when they crack open a window.
 
Thats why i was thinking of giving the room its own fresh air supply and sealing the door. Just didnt know if anyone had any other recommendations.
 
From outdoors is the best. You can use indoor air per code but the communicable spaces have to have 50 cubic feet of volume per 1000 BTU/h of the appliance. Residential applications rarely meet this provision. You can use either one or two permanent openings to accomplish combustion air. Either one within 12" of the ceiling with a free area of 1 square inch per 3000 BTU/h or two openings, one within 12" of the ceiling and one within 12" of the floor with somewhere between 1 square inch of free area per 2000 BTU/h or 4000 BTU/h depending if the openings are horizontal or vertical.

*disclaimer - recalling these numbers from memory. The effort is there but the actual numbers may vary...
 
Ok, so i definitely need to bring in outside air. Ive been calling it a room, but its more like a small closet. Barely big enough to house the water heater. The water heater is 40k BTU in a 4x3x8 room (not even 96 cuft). Also going by your numbers with 40K BTU's Id need at least a single 6" inlet.

Thanks for the info, I've never really liked having this thing stuck in the closet with no ventilation anyways. The part that sucks is the vent going to have to go on the front of my house, by the front door. Now I gotta figure a way to make it blend in... or see if I can run it up to my soffit
 
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I dont think by code you could. I am not a code official however LOL

Take it out and put in an electric or electric tankless. I never understood the appeal of a gas HWH.
 
Electric.... Naaa, thats not gonna happen. I've had electric water heaters in the past and they just dont recover as well as gas. I wish I had all gas appliances and will slowly convert all to gas. A gas tankless is in the plans for the future but this one is <2 years old, so its got some life left before it gets replaced. After looking at it closer it looks like I will be able to run the vent into the soffit over my front porch where it wont be so visible. Hopefully this will alleviate any more issues I have.

Thanks for the help and info guys.
 
Lankford said:
From outdoors is the best. You can use indoor air per code but the communicable spaces have to have 50 cubic feet of volume per 1000 BTU/h of the appliance. Residential applications rarely meet this provision. You can use either one or two permanent openings to accomplish combustion air. Either one within 12" of the ceiling with a free area of 1 square inch per 3000 BTU/h or two openings, one within 12" of the ceiling and one within 12" of the floor with somewhere between 1 square inch of free area per 2000 BTU/h or 4000 BTU/h depending if the openings are horizontal or vertical.

*disclaimer - recalling these numbers from memory. The effort is there but the actual numbers may vary...
Click to expand...
Your numbers are spot on.

You can vent outlet air to an attic, provided that the attic is ventilated with louvers on both ends. To calculate the outlet air connection, you would use 2 square inches per 1000 btu of appliance rating (80 square inches for you).

Louver size is based on net free area. If you don't know the net free on your louvers, wood is assumed at 25 percent free, metal at 75 percent. Screen is required and may not be smaller than 1/4 of an inch.

What type of room does your appliance closet open into? You may be able to get some indoor combustion air that way by cutting a vent in the closet door. My gas hwh uses combustion air from my kitchen.

As an aside, if you want to check out anything in the code book yourself, you want to look in the NC Fuel Gas code, not the mechanical code book.
 
The door opens in the foyer right by the front door. I had thought about venting the door but my main issue is the back drafting into thehouse. With my crawl space being sealed the house is much tighter, I've noticed a decrease in my utility bills since last Jan. already. I have been burning a fire lately too and thats probably why air is being pulled through the kitchen vent and hwh flue.(didnt quite hit me at first). That's why I was planning on just sealing the door with weather strip and providing the hwh with outside air for combustion. Here's a few pics....


Front door, closet to the left
IMAG1399.jpg


HWH
IMAG1400.jpg
IMAG1401.jpg


melted indicators from backdrafting
IMAG1402 (1).jpg
 
ponykilr said:
I never understood the appeal of a gas HWH.
Click to expand...

They heat water faster and more inexpensively than their electric counterparts. Gas is objectively better by every performance metric.
 
So wait, there are NO openings in that closet? Just the gas vent on top? That's absolutely terrifying. Another item of note that I do not see, do you have a shutoff valve for the gas line before it runs into the water heater regulator?

I'd look at the two opening method, one into the attic and one going outside. Do they offer like a homeowners crash course in to the code books? Like a 1 or two day weekend deal? I have taken the full code class for mechanical, but it was 2 weekends of 8 hour classes, maybe a little much for someone not in the field.
 
One of the problems with gas water heaters is combustion (fresh or outside air) air and flue gas air . One goes in one goes out. there are rules to do it properly. Can you put water heater somewhere else? Like in an outside storage area or attic? Sealing the crawl space changes air into house. Your water heater problems may have alerted you to a larger problem. Is one wall of closet an exterior wall if so then cut two proper size holes in wall to outside, one high and one low with insect screens. Then install weather stripping on closet door. You also can add some outside air to your hvac unit to add more air to house interior which will help when kitchen hood, bathroom fans, and clothes dryer are operating.
 
There is a shut off where the gas line enters the room, but there is no other air inlet except the gap beneath the door. I havent ever noticed the backdraft until the other day (the coldest day of the year). Moving it is pretty much out of the question bc then I'd have to re plumb most of the house. I kinda like having it where its at also. It's centrally located and doesnt take long to get hotwater anywhere in the house. Think I'm just gonna do the 2 vent method and seal the closet door.
 
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