Fresh Air Vent In Ducting?

carlspackler

I went to install some canned lighting in a basement ceiling and ran into an issue. This house was built in the mid 60's and ran an oil fired furnace. It was switched over to a natural gas Lennox system in the 70's. I noticed this vent pipe that's about 6 inches round and leads from the outside along a joist all of the way to the furnace return air duct. I believe the vent has a valve in it that allows you to close it (and I believe it is closed.) You think this was a fresh air intake for the oil fired furnace system? I would love to cut it out while I'm up there but need to know for sure it's of no use. I felt no suction when the furnace was turned on.

There is also a control near the thermostat in the house that is an air controller from Mammoth Industries and Honeywell. I don't think it is being used as it has always been off.

Byproducts of the olf oil fired furnace system?

Thanks in advance for your help.

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MarQ Remodeling (no website)

carlspackler

Any ideas on this setup?

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MarQ Remodeling (no website)

mdshunk

Fresh air intakes are there to prevent backdrafting and air starvation for fuel burning appliances. Tight homes that have fireplaces, fossil fuel furnaces, gas water heaters and dryers, and exhaust fans normally have fresh air intakes to the return ductwork to equalize the pressure in the house. There's really no "suction" on the f/a pipe. The will only inhale when negative pressure is approached in the house. If people are in and out of the doors regularly, they will not inhale. A 6" pipe does seem large to me. They are normally 4". If the original system designed determined that there needed to be a fresh air intake, it should stay. Eliminating it risks the possibility of CO spilling out of the furnace if a negative pressure condition develops. You can re-route it, if that would get it out of your way better. There is no special science to the routing of the f/a pipe to the return side. It can exit the home anywhere, and hit the return anywhere.

carlspackler

Thanks for the reply. That makes sense to me. I'll look for another way.

Edit: I also wanted to add that I've reviewed a lot of schematics on the web for gas forced air systems and none of them have an exterior venting that routes through the return air duct.

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MarQ Remodeling (no website)

Hurley

There's a chance the vent might be a juryrigged atemp at an HRV. Heat Recovery Ventilator. If it is there would also be a similar vent on the pressure side that criscrosses with the one you found. The idea being to bring fresh air into the house in winter when when it might get a little stale.

carlspackler

Is all this necessary? I thought these systems were closed systems with no external air needed. This house wasn't built very tight either.

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MarQ Remodeling (no website)

Hurley

Not at all. HRV's are add ons after the fact and have no effect on how the furnace runs.