Cold draft from range hood. Do I need to add a damper?

shamu1023

I have a large range hood, 1000cfm.

It's either 8 or 10 in solid pipe from kitchen to the roof.

The roof has a combo cap and damper.

I'm in Michigan, and get a cold draft still from the hood. I checked roof cap, and the damper appears closed. So, where is cold air coming from? Is it just the outside air is making the cap cold, then the pipe cold, and the cold air just falls naturally?

Do I need to add another damper inside, between the end of the pipe and my range hood?

Is there something else I should check?

Thanks in advance.

bjohnhy

Make sure no breaks in that exhaust pipe, such as in attic.

But the house may have enough negative pressure to draw air in around/through the closed damper. Those dampers are usually not perfect. Do you have leaky ceiling elsewhere in house creating stack effect?

shamu1023

Thanks...

Regarding Stack effect, leaky ceiling... probably, as it's a 1960 home, so it's definitely not sealed well.

How do identidy the issue? How do I fix that?

rynoheat

Get an energy audit, sometimes you can get them for free through your state. They will use thermal cameras, a blower door test and sometimes a smoke machine to find out where your air infiltration issues are. It's usually worth it even if you have to pay for it.

Stopping air infiltration is the best way to save energy costs, especially in an older home.

Dennis

How much of the pipe is extending out the roof an how much in running through a cold unconditioned attic?
What you might be feeling is convection currents, not damper leakage. Warm air will rise through the duct and displace the cold air downward. The solution is a damper at the range hood or as close to it as possible.

HVACNUT

Is the fan in the range hood? If there's access near the roof line, the make butterfly dampers specifically for that purpose. It comes as a section of pipe with the damper already installed.