Make up Air Vent, What to do With It?

[notlohdahc]

I recently married and moved into my now wife's home. Her home is 7 years old and located in Wisconsin.

She has already put me to work on a project to finish off the basement.

While figuring out what I needed to do down there I noticed what I believe is a make-up air vent. It is not connected to our furnace and does not contain any kind of damper.

The 6 inch duct comes in maybe a foot into the basement then curves down 90 degrees and has a plastic vent cap on the end that can be removed. Standing under it I can feel a constant draft coming into the basement.

I've temporarily plugged the duct with insulation until I figure out what needs to be done with it.

So, that is my question . . . What do I need to do with this vent?? Leave it plugged? Seal it off permanently? Install a damper and leave it disconnected from the furnace? Connect it to the furnace with a damper via the cold air return? Connect it to the furnace without a damper via the cold air return? Unplug it and leave it as is?

I can say this, now that it is plugged, the temperature in the basement has gone up almost 5 degrees. I've always thought the basement was cooler than normal even for winter so I put a thermometer down there last month. Prior to plugging this vent, the temps in the basement were around 58 - 60 degrees. With this vent plugged, temps are constantly above 62 degrees.

Thank you!

[Bud9051]

You say it is powered, so It sounds like it has a motorized damper inside. Those are good, but when they are necessary they have to be an approved part of the system. Necessary means someone has determined that the furnace NEEDS an outside air source as determined with a worst case test. In other words, it may not look like it is necessary, but it might be. To block it with insulation and unplug it without knowing why it was installed would not be advisable.

Now, 7 years ago, someone might have built a very tight home and thus outside air was necessary. In any case, outside combustion air entering where you need it is better than it being pushed in through the walls. What goes out will need to be replaced.

One option is an outside combustion air kit. It eliminates the cold air when you don't want it, but provides the combustion air when the furnace needs it.

If that duct was intended to be a fresh air source, similar discussion in that it may be needed.

Any idea as to whether this is a fresh air source or a combustion air source?

Bud

[Concretemasonry]

That sounds like a very common fresh air intake to the furnace in a cold weather climate and is often required by code. The concept is not used with high efficiency furnaces and I could not justify the problems and complexities and went with an 80% furnace a couple of years ago because our heating for 1400 sf needs are not that much (never over $80/mo including water heating and connection charges and taxes).

Usually, there is a flex vent running down into something like a 5 gallon pail on the floor that causes a break in the thermal suction and exterior air is drawn in when only when there is negative pressure inside.

I have one in my townhouse (and every unit has a similar set-up) and it is in my utility room where it also serves to provide make-up air for my gas water heater when needed. Mine is only about 3 gallon because of space requirements and the fact that we have a second refrigerator in the room.

I did not catch that the OP said it was powered, but it there could be a direct connection made to the furnace if there is no gas water heater.

Do not make the "vent" you discovered connected to any part of the return air system or the entire distribution system could be upset.

Dick

[Bud9051]

I stand corrected Dick, his plugged and unplugged was referring to the fiberglass stuffed into the duct. I was hoping for a controlled damper.

Bud

[notlohdahc]

It is not powered in anyway, just a 6 inch tube, no damper, coming into the basement.

I gather from posts so far, that attaching a flex tube and running it down the wall to a bucket will stop the draft I am getting from the current setup. Do I need to install a damper with this setup?

I am looking for a solution that allows this vent to be usable, but I want the constant draft eliminated.

[Concretemasonry]

I just bought the townhouse the way they were all fitted out.

It seems to work and we use the room to dry out some laundry for a couple of hours and when the door to the room is closed the room is warm.

The strange thing is that the utility room is not as warm in the warmer days, so we just close the door to keep the heat in when it is cold. I think a lot of it has to do with the thermal inertia of the surrounding block walls to even out temperatures and humidity.

Dick