HVAC questions - Too much fresh air intake, sucking in bad smells.

[ExtraSlow]

oh hai guyz! I'm a total HVAC newb, so I'd love some input from someone who knows more about this stuff.

My HVAC is sucking in exterior smells. Like if a skunk walks through my yard, or the neighbors have friends over who smoke, or if there's forest fire smoke in the air. That smell gets sucked in and distributed around my house immediately. It's bad.

The house was built in 2008 or so and it's a "mid" efficiency furnace I think. Not High anyway, vents out conventional chimney in roof not side wall. I run the furnace fan 24/7 to help even out the temperatures in my house, because it's 2 stories and if I don't the back bedrooms get scorching hot in the summer, and stay quite cool in the winter. So, I run that furnace fan 24/7.

I leave my ventilation fan, that one that sucks from cold air return and exhausts outside OFF all the time.
My furnace has two fresh air intakes. One that goes to the side of the furnace and is open and another that goes directly to the cold air return side of the furnace. after investigating these two intakes, it's clear the one that goes to the cold air side of the furnace is sucking in quite a bit of air.

So, I want to continue to run the furnace fan 24/7 to keep house temps even, but I want that one intake to draw in less/no fresh air. Can I shut it down without causing a big issue? Will that somehow mess up the air balance in my house or something? Have I been explaining this well?

Here's the two air intakes because I know people love pictures.

[revelations]

This is probably not the 'correct' way to do it, but I cut off the external furnace intake completely and control the airflow recirc with windows. Even in the winter I have a window in the basement open a crack (we do have HE furnaces though so they have their own intake/exhaust). When skunks strike, I just close the window(s).

I monitor the indoor air quality with several foobot devices.

[Darell_n]

Don’t touch the duct in first picture. In the second picture there is a metal handle that should have a damper blade behind it, turn that 90° to close it and stop the smells from outside. You should probably remove the flexible duct and look inside to make sure there is actually a blade behind it, as I’ve seen many cut off. A new damper is around $2-3 at Home Depot.

[ExtraSlow]

So here's a question. If the one intake that comes in low is for combustion air, what is the purpose of the intake that connects to cold air side of furnace? Do you need that at all? Could I just block it?

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Don’t touch the duct in first picture. In the second picture there is a metal handle that should have a damper blade behind it, turn that 90° to close it and stop the smells from outside. You should probably remove the flexible duct and look inside to make sure there is actually a blade behind it, as I’ve seen many cut off. A new damper is around $2-3 at Home Depot.

Wow you typed just as I was typing. So, what's the point of that intake anyway?

[Darell_n]

It is just for fresh air. 10% minimum fresh air is basically a starting point for commercial buildings to prevent sick building syndrome. Like cracking a window in your car while parked. It will also keep the house slightly pressurized with the fan running and prevent winter issues like windows and doors freezing shut.

[suntan]

I bought those really expensive 3M filters last summer because of the smoke, and it worked wonders. I switched them out after one month. They were dark brown.

[revelations]

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I bought those really expensive 3M filters last summer because of the smoke, and it worked wonders. I switched them out after one month. They were dark brown.

Thats exactly what we did too - and why I did not want a 'fresh' air intake open 100% of the time. The AQ in the house definitely improved as measured by our Foobot

[ExtraSlow]

So, I realized the damper on the fresh air intake didn't seem to do much, and today I figured out why. It looked like this:

If you can't tell, that's a 4" damper inside a 5" pipe. It's yand-made too. I'm guessing the original HVAC guy didn't have the correct 5" damper handy and didn't want to go buy one so he built something that looked good enough and called it a day.
Installed the correct 5" damper:


I have the new damper set in the closed position and the airflow is now clearly reduced, but not zero. Since I'm measuring by putting my hand over the intake, I can't be more precise than that.

Anyway, we'll see if this is sufficient or if I want to eventually want to close that off completely.

I think this should help reduce exterior smells, reduce AC and heat needs, as well as increase indoor humidity in the winter, which has always been unbearably low in this house.

Thanks everyone!

[revelations]

We had stupid low humidity in the house too, until I got a drum humidifier. Needs more maintenance though - but so nice when its -25c out to have 40% humidity inside.

[ExtraSlow]

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We had stupid low humidity in the house too, until I got a drum humidifier. Needs more maintenance though - but so nice when its -25c out to have 40% humidity inside.

My problems couldn't be explained by poor humidifer performance alone. Although that's a factor for sure.

[revelations]

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My problems couldn't be explained by poor humidifer performance alone. Although that's a factor for sure.

You would have to quantify what levels of RH you have indoors during the cold spells. I know for me, anything below 30% and I start to get nosebleeds, etc.

[jeffh]

That smaller damper is a standard residential install around here. I believe they do that, so the operator can’t ‘completely’ close off the fresh air intake. That damper and pipe were supposed to be sized and balanced to suit your homes individual air change requirements as per building code.
Your problem may be more centric on where the inlet is on the exterior of your home, as yours just may be in a bad spot for thw wind to bring the stink your way.
To limit the air coming into your home unimpeded by the combustion air pot near your furnace, there is a couple things you could do. One is to have a hoyme or barometeic damper installed, which would open or close based on gas fired appliance needs. Or you could remove it entirely, and replace your furnace and hot water tank with direct vent appliances.

[outsider]

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Don’t touch the duct in first picture. In the second picture there is a metal handle that should have a damper blade behind it, turn that 90° to close it and stop the smells from outside. You should probably remove the flexible duct and look inside to make sure there is actually a blade behind it, as I’ve seen many cut off. A new damper is around $2-3 at Home Depot.

Question for you. My cold air intake isn't attached to anything and is sitting on the floor. Should I go about moving off the floor or is it ok that way?

[Darell_n]

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Question for you. My cold air intake isn't attached to anything and is sitting on the floor. Should I go about moving off the floor or is it ok that way?

Referring to the photos at the start of this thread, which intake is laying on the floor? If you only have one, that is your combustion air and it should be close to the hot water tank / furnace burners. You can simply throw the end of it into a larger plastic garbage can to prevent it from spilling cold air into the basement when no burner is on.

[outsider]

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Referring to the photos at the start of this thread, which intake is laying on the floor? If you only have one, that is your combustion air and it should be close to the hot water tank / furnace burners. You can simply throw the end of it into a larger plastic garbage can to prevent it from spilling cold air into the basement when no burner is on.

Attachment 88389

I attached a terrible photo I took. You can see it on the floor. Could I just put it on top of say a cardboard box to lift it off the ground?Attachment 88389

[Darell_n]

That looks fine. Just screw it to the duct at floor level, if it’s not attached to anything.