Water heater venting problem in Winter

[lhort]

Hi. I am having an issue with my water heater and would like some advice. Water heater is LP gas, located a few inches away from the basement wall with a vertical rise of 18 inches going straight up to the elbow with a proper pitch. All piping going out of the house meets code, doubled wall pipe, exhaust pipe above roof. I live in New York and if the weather is very cold (0-20 degrees or so) the fumes occasionally can be smelled in the basement. When this happens, the pipes are cold and have condensation, if I open the outside door to provide a draft then the pipe warms up and the fumes go up the exhaust pipe. However, now it seems that this is happening occasionally when the weather is in the lower 30s. My house is not super tight or energy efficient so a draft issue shouldn't really be a problem. There is no blockage in the vent pipes. I have a carbon monoxide monitor and it has never gone off. I am looking for a solution to this problem.

Could it possibly have anything to do with my heater being older and maybe doesn't burn as hot as it should to warm the exhaust pipe in cold weather? Could replacing this water heater with a new one be a solution to the problem?

Thank you

 

[Jadnashua]

There are industry guidelines on how much room volume a burner needs based on its BTU rating. There is often a more specific guideline in the installation manual.

I know when I was considering a new boiler, I looked at several options, and found that the volume of the room where it needed to go was insufficient based on those guidelines. The alternatives were, use a different boiler that used closed combustion, or add in an atmospheric vent to the outside to provide the needed combustion air. The tighter the house, the worse it gets. If you do not have enough free air, the draft on the burner may not support proper operation of the burner. It can be a self-propagating problem...not enough air, burner is not as hot, making the draft worse.

How big is the burner on the thing?
How large is the room (HxWxL)?

Keep in mind...all of that air that goes out the flue needs to be replaced by fresh air coming into the burner. In a conventional burner, that air typically comes in through cracks in the foundation, walls, or other penetrations. As people tighten up their houses or buy a bigger device, that load increases. A burner won't vent properly unless it is getting enough replacement air. Since you likely have paid to condition that air, it really makes sense to consider upping the game and use a closed combustion burner system that then uses outside air for the combustion process, not the air from within your home that you then throw out the flue.

 

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[Dana]

Hi. I am having an issue with my water heater and would like some advice. Water heater is LP gas, located a few inches away from the basement wall with a vertical rise of 18 inches going straight up to the elbow with a proper pitch. All piping going out of the house meets code, doubled wall pipe, exhaust pipe above roof. I live in New York and if the weather is very cold (0-20 degrees or so) the fumes occasionally can be smelled in the basement. When this happens, the pipes are cold and have condensation, if I open the outside door to provide a draft then the pipe warms up and the fumes go up the exhaust pipe. However, now it seems that this is happening occasionally when the weather is in the lower 30s. My house is not super tight or energy efficient so a draft issue shouldn't really be a problem. There is no blockage in the vent pipes. I have a carbon monoxide monitor and it has never gone off. I am looking for a solution to this problem.

Could it possibly have anything to do with my heater being older and maybe doesn't burn as hot as it should to warm the exhaust pipe in cold weather? Could replacing this water heater with a new one be a solution to the problem?

Thank you

Does any of the vent pipe travel up the outside of the house?

Is it vented into a masonry chimney? If yes, does the chimney also vent a furnace or boiler (or did it used to be shared by a furnace or boiler?_

What is the total vertical distance from the draft hood on the water heater to the top of the flue?

Is your house heated by ducted hot air?

Duct imbalances on the heating can result in air-handler induced depressurization of the basement, which can overcome normal stack effect pressures, and backdraft the flue. This is more likely to happen when stack is cold than when the burner has been running for awhile. But once the flue has been actively chilled below some point it creates an "anti" stack effect when there is no burner adding heat to the stack, and cold air will continue to come down the flue until the flue warms up again (from either the burner firing for some period, or more slowly from the heat of the house.)

The taller the stack and the greater fraction of it that is within insulated conditioned space, the better the stack-effect draft is. But if you have tall well-ventilated attic that the flue runs through it could get cold enough between burns that it backdrafts on it's own simply from stack effect forces until the burner heats it up again. It can be complicated to analyze fully even on-site, harder still on a web forum.

If you have ducted air heating, with a smoke pencil, stick of incense or something try testing the direction of flow at the draft hood on the water heater (when the heater's burner is off), under a variety of conditions when the air handler is running. Open & close doors to different rooms to see if it ever changes. Rooms with supply-only registers and no dedicated returns are prime suspects, since a supply-duct-only pressurizes that room, and the "great outdoors" becomes part of the return path, possibly via the water heater flue.

Venting into an oversized flue that it used to share with another burner (but no longer does), is a classic "orphaned water heater" case, which will backdraft fairly readily under a variety of conditions.

You'll only get sufficient carbon monoxide to trigger the detector if there is something off with the burner, but that doesn't mean you want to be breathing the other exhaust products.

 

[lhort]

There are industry guidelines on how much room volume a burner needs based on its BTU rating. There is often a more specific guideline in the installation manual.

I know when I was considering a new boiler, I looked at several options, and found that the volume of the room where it needed to go was insufficient based on those guidelines. The alternatives were, use a different boiler that used closed combustion, or add in an atmospheric vent to the outside to provide the needed combustion air. The tighter the house, the worse it gets. If you do not have enough free air, the draft on the burner may not support proper operation of the burner. It can be a self-propagating problem...not enough air, burner is not as hot, making the draft worse.

How big is the burner on the thing?
How large is the room (HxWxL)?

Keep in mind...all of that air that goes out the flue needs to be replaced by fresh air coming into the burner. In a conventional burner, that air typically comes in through cracks in the foundation, walls, or other penetrations. As people tighten up their houses or buy a bigger device, that load increases. A burner won't vent properly unless it is getting enough replacement air. Since you likely have paid to condition that air, it really makes sense to consider upping the game and use a closed combustion burner system that then uses outside air for the combustion process, not the air from within your home that you then throw out the flue.

 

[lhort]

There are industry guidelines on how much room volume a burner needs based on its BTU rating. There is often a more specific guideline in the installation manual.

I know when I was considering a new boiler, I looked at several options, and found that the volume of the room where it needed to go was insufficient based on those guidelines. The alternatives were, use a different boiler that used closed combustion, or add in an atmospheric vent to the outside to provide the needed combustion air. The tighter the house, the worse it gets. If you do not have enough free air, the draft on the burner may not support proper operation of the burner. It can be a self-propagating problem...not enough air, burner is not as hot, making the draft worse.

How big is the burner on the thing?
How large is the room (HxWxL)?

Keep in mind...all of that air that goes out the flue needs to be replaced by fresh air coming into the burner. In a conventional burner, that air typically comes in through cracks in the foundation, walls, or other penetrations. As people tighten up their houses or buy a bigger device, that load increases. A burner won't vent properly unless it is getting enough replacement air. Since you likely have paid to condition that air, it really makes sense to consider upping the game and use a closed combustion burner system that then uses outside air for the combustion process, not the air from within your home that you then throw out the flue.

Hi, basement is about 30 x 40. Hot water heater is 40 gallon
I understand about the replacement air, but nothing has changed ventilation wise in my house, so why the venting problem now? That's what's puzzling me.

 

[Dana]

Something clearly HAS changed in the ventilation profile of your house, you just haven't figured out what that is yet. Even if you never figure it out there may be good solutions, but without more information it's hard to advise. It's tough to make intelligent conjectures or suggest experiments without more basic information:

Is the flue for the water heater shared with other appliances? Y/N

Does the flue run primarily outside of the thermal boundary of the house (eg, a masonry chimney on an exterior wall), or inside?

The flue size is...? The BTU/hr rating of the water heater burner is...? (or just the model number so it that can be looked up.)

New York is a big state, spanning US climate zones 4A through 7A. Not that it should make a huge difference, it might- have a ZIP code?

 

[Jadnashua]

Something as simple as running the dryer, the stove's hood vent, the furnace, or maybe even a bathroom exhaust fan can upset the balance of things. They call venting of a flue the 'draft' for a reason...it requires air movement. Installed new windows or a door? Done any seam caulking? Is there any obstruction in the flue (leaves, bird nest, dead squirrel)?

The newest WH designs can be disrupted by lint on their inlet air vent screen (design varies by company, but its intent is to prevent igniting any flammable vapors, preventing an explosion).