Backdraft on New Install

[John Sullivan]

We recently installed a new Bradford White (replacing a 22 yr old Bradford White) gas water heater. We used the old venting which has the small turn pictured then goes up 10 ft and has a 6 foot section in the attic which goes over at ~45* angle and vents out the roof. The vent is dedicated hasn't ever shared with furnace. The water heater is located in our garage, I need to explore if it's not getting enough make up air when garage doors are shut but trying to cross everything else off the list too.

I need to get up and make sure the vent isn't plugged up on the roof but there is a cap on it. I'm concerned about the change in vent size pictured - it wasn't a problem with the old water heater but if it might be the cause of backdraft with the new system of if I should be looking at other reasons.

Anyone have any other ideas?

 

[breplum]

The 3" single wall flue going in to double wall flue is more or less ok.
Code normally only wants a double wall flue adapter, then all double wall in unconditioned space. Reason is to maximize draft by not having the cold single wall pipe create cold mass of air to overcome. The flue run you describe sounds fine.

 

[John Sullivan]

Thanks for your thoughts.

It would have been nice if it was a matter of changing out fitting, but probably an issue of lack of make up air in the garage I guess. I'll have to figure out the easiest way to do that, probably have to install some ducting on the side of the garage I guess, I can see if leaving the garage door open a crack solves the problem temporarily.

Anything else you can think of I should be on the look out for?

 

[RonAKA]

Holding a BBQ lighter flame near the vent cone will help you determine how much draw is being established. You could test it with and without your garage door open. If it is not drawing with the garage door closed then a 3" fresh air vent into the garage should help. Not sure why the old one would work, but not the new though.

 

[Bird Doo Head]

Perhaps an Automatic Make Up Air Damper will help in your situation.

Search for Make Up Air Damper, Combustion Air Damper, Relief Damper, Barometric Damper and Backdraft Damper.

They come in many types:
Some have tubes leading to a manometer switch. When the water heater fires and creates negative pressure in the building, the switch will sense the difference between indoor & outdoor pressure and a motor will open the damper. Depending on the heater, some can be wired in series with the burner control to stop the heater if the make up damper fails to open. ($$$)

Others have a simple flap with a weight. It takes a little trial and error to set the weight, but once set it is good for life. Usually those are titled Barometric Damper (Picture is attached below) ($$)

In the way back, the heating people would run a piece of duct from outside (maybe through a window) down to the floor level, ending near the burner. At the bottom they'd make a sort of P-trap. When the heater came on and combustion air was needed, outside air was drawn through the tubing & into the building. When the heater was off, no air was needed and the p-trap stopped breezes. No moving parts to fail.
Running the duct into an empty gallon paint bucket (no p-trap) works, too, to stop the breeze. ($)

With any option, you have to figure out the size of duct opening required by using the BTU rating for your water heater & all other air using devices in the room. (Furnace, space heater, etc.) Charts and formulas for this are easy to find on line.

Worst Case: A Tjerlund fan on the heater's vent pipe with a screened opening or passive roof vent in the building. ($$$$)

A short article about combustion air requirements is here: Boiler/Burner Combustion Air Supply Requirements and Maintenance

Also- It's CRITICAL that your garage has a carbon monoxide detector.

Paul

 

[John Sullivan]

Perhaps an Automatic Make Up Air Damper will help in your situation.

Search for Make Up Air Damper, Combustion Air Damper, Relief Damper, Barometric Damper and Backdraft Damper.

They come in many types:
Some have tubes leading to a manometer switch. When the water heater fires and creates negative pressure in the building, the switch will sense the difference between indoor & outdoor pressure and a motor will open the damper. Depending on the heater, some can be wired in series with the burner control to stop the heater if the make up damper fails to open. ($$$)

Others have a simple flap with a weight. It takes a little trial and error to set the weight, but once set it is good for life. Usually those are titled Barometric Damper (Picture is attached below) ($$)

In the way back, the heating people would run a piece of duct from outside (maybe through a window) down to the floor level, ending near the burner. At the bottom they'd make a sort of P-trap. When the heater came on and combustion air was needed, outside air was drawn through the tubing & into the building. When the heater was off, no air was needed and the p-trap stopped breezes. No moving parts to fail.
Running the duct into an empty gallon paint bucket (no p-trap) works, too, to stop the breeze. ($)

With any option, you have to figure out the size of duct opening required by using the BTU rating for your water heater & all other air using devices in the room. (Furnace, space heater, etc.) Charts and formulas for this are easy to find on line.

Worst Case: A Tjerlund fan on the heater's vent pipe with a screened opening or passive roof vent in the building. ($$$$)

A short article about combustion air requirements is here: Boiler/Burner Combustion Air Supply Requirements and Maintenance

Also- It's CRITICAL that your garage has a carbon monoxide detector.

Paul

Thank you for the detailed response. I installed a carbon monoxide detector right away when I realized it wasn't going to be fixed right away. I didn't want to be worried every time I opened the door to the garage. Luckily it hasn't gone off in the last week (after making sure it had fresh batteries and tested before install).

If I install a damper on an outside wall in the same room does it matter how far away from the burner it is? Ideally I would install the damper on the far side of the garage, ~30 ft from the water heater.

 

[Bird Doo Head]

If I install a damper on an outside wall in the same room does it matter how far away from the burner it is? Ideally I would install the damper on the far side of the garage, ~30 ft from the water heater.

Functionality wise, distance won't matter.
Think of it this way: The burner comes on and tries to exhaust flue gasses. This creates a negative pressure in the building. As long as replacement ("make up") air can get in the room anywhere, the building pressure will be neutral, allowing flue gasses to easily rise up the vent pipe.

But... The closer to the burner the damper or outside air opening is, the less cold air there will be traveling across the floor.

Also note that a barometric damper usually won't open unless combustion air is needed, but sometimes indoor-outdoor pressure differential can cause them to flap partly open for a second. (Like when opening the door on a windy day.)

 

[John Sullivan]

Thank you, that's what made sense to me, but I kept seeing videos where the make up air vent is place right next to it, which makes sense I guess when you don't want to create a draft in the house. Good to know it wasn't something I just wasn't considering.