# Anybody know what this is for?



## stickman1978 (Sep 15, 2011)

In the basement next to the cold air intake for the furnace.


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## sparky18181 (Apr 17, 2012)

Old dryer vent?


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## Waif (Oct 27, 2013)

Some furnaces had a "make up" air intake.
A hose to near floor from a through wall device similar to yours.
Mine has fiberglass insulation stuffed in the end to reduce bug intrusion.


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## stickman1978 (Sep 15, 2011)

sparky18181 said:


> Old dryer vent?


There is a laundry room on the second floor. House is basically new 11 years old.


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## stickman1978 (Sep 15, 2011)

Waif said:


> Some furnaces had a "make up" air intake.
> A hose to near floor from a through wall device similar to yours.
> Mine has fiberglass insulation stuffed in the end to reduce bug intrusion.


There is already a make up air vent right next to this.


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## stickman1978 (Sep 15, 2011)




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## sparky18181 (Apr 17, 2012)

Maybe at one time there was a dryer down there.


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## stickman1978 (Sep 15, 2011)

sparky18181 said:


> Maybe at one time there was a dryer down there.


There is no other hook ups in that area. 220 or gas line. No water either for a washer.


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## Waif (Oct 27, 2013)

stickman1978 said:


> View attachment 800887


Not make up air to furnace. Just air to allow equalization of pressure of basement/house.


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## onlinebiker (Sep 19, 2019)

Pet door for spiders and cockroaches...


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## Matty Patty (Oct 9, 2019)

Looks like an air intake vent for atmospheric combustion appliances. (Right side pipe in diagram) helps with using outside air for combustion vs sucking surrounding inside oxygen from inside the house.









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## onlinebiker (Sep 19, 2019)

Dupe post.


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## stickman1978 (Sep 15, 2011)

Waif said:


> Not make up air to furnace. Just air to allow equalization of pressure of basement/house.


Was kind of thinking those lines also. But doesn't that happen with the outside air coming in the makeup vent?


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## stickman1978 (Sep 15, 2011)

Matty Patty said:


> Looks like an air intake vent for atmospheric combustion appliances. (Right side pipe in diagram) helps with using outside air for combustion vs sucking surrounding inside oxygen from inside the house.
> 
> 
> 
> ...


That is already there. Grey vent in second picture.


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## MEL (Jul 17, 2005)

Was / is there a basement bathroom? Basement bath vent fan


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## TK81 (Mar 28, 2009)

That's where you exhaust the smell of the green as it dries in the basement. You'd stink up the whole house without it. Just put a fan on low on the far wall and you'll be good.


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## Waif (Oct 27, 2013)

stickman1978 said:


> Was kind of thinking those lines also. But doesn't that happen with the outside air coming in the makeup vent?


It should.
I thought it odd too. Stuck me as redundancy.
Original furnace (since replaced) was new about twenty years ago.
The flange outside the wall has two grates. Inside , two flanges the hoses fit to.
One just drops to near floor. Not unlike the illustration above.

Air balance/makeup was a deal in a paint shop I worked in. 
How air flows by amount of intake vs exhaust .
Exterior weather conditions could change that.
As could resistance as filters loaded up.

Maybe someone was growing hooter in your basement and wanted more fresh air , l.o.l..


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## Matty Patty (Oct 9, 2019)

stickman1978 said:


> That is already there. Grey vent in second picture.


Does the one in the second picture go next to the furnace by the floor? Or does it go into the return side of the ductwork? Basically do you have 2 of the grey vents and the open hole (first picture / 3 total) or just one grey vent and an the open vent from picture one? (2 total)

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## bobberbill (Apr 5, 2011)

My mom's house in town had one. You could see where it was hooked to the cold air return plenum. It was capped off.


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## Wasman2. (Jan 13, 2018)

Grow room vent.


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## stickman1978 (Sep 15, 2011)

MEL said:


> Was / is there a basement bathroom? Basement bath vent fan


Nope


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## Nostromo (Feb 14, 2012)

I'm pretty sure it's for makeup air. Or, the previous resident had equipment that required venting to the outside


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## stickman1978 (Sep 15, 2011)

Matty Patty said:


> Does the one in the second picture go next to the furnace by the floor? Or does it go into the return side of the ductwork? Basically do you have 2 of the grey vents and the open hole (first picture / 3 total) or just one grey vent and an the open vent from picture one? (2 total)
> 
> Sent from my SM-G965U using Tapatalk


Not by floor but it is the intake side.


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## stickman1978 (Sep 15, 2011)

Nostromo said:


> I'm pretty sure it's for makeup air. Or, the previous resident had equipment that required venting to the outside


Just trying to figure out if we should plug with insulation or not. We are getting makeup air already.


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## Matty Patty (Oct 9, 2019)

stickman1978 said:


> Not by floor but it is the intake side.
> View attachment 800902


Intake side to the return side of main duct work? Can you post a picture where the grey vent goes?

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## stickman1978 (Sep 15, 2011)

Matty Patty said:


> Intake side to the return side of main duct work? Can you post a picture where the grey vent goes?
> 
> Sent from my SM-G965U using Tapatalk


That would be the third pic. It goes from exterior wall to intake side of furnace.


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## Matty Patty (Oct 9, 2019)

stickman1978 said:


> That would be the third pic. It goes from exterior wall to intake side of furnace.


Ok then the first picture is the combustion air intake for the furnace/hot water tank.

Typically code calls for fresh air intake (2nd picture going into the duck work) AND a combustion air intake (first picture). They are 2 different things for different purposes that make the home comfortable and safe. 

Newer homes like yours are usually built "tight/more efficient" (less air leakage) vs older home that are drafty (lots of air leakage/less efficient)

Some info on the first picture below and hope this helps. 









Combustion Air Ducts, Part I: Why Houses Need Them


Homeowners, builders, and insulation contractors spend lots of time trying to seal up every little air leak in to a house, but then the building code requires this big hole that allows cold air to just dump in to the basement. Silly, right?




structuretech.com





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## Gamekeeper (Oct 9, 2015)

stickman1978 said:


> Just trying to figure out if we should plug with insulation or not. We are getting makeup air already.


Close all your doors and windows, turn on the kitchen stove, range hood, bathroom fans, turn on your dryer, run the hot water, turn the furnace up to 80, and then go down in the basement and hold a lighter up by that hole.

That’s about the simplest way to check for make up air that I can remember.

seemed like there was a symptom where you get dust deposits a certain distance away from outside walls as well, but you’ll know in a hurry if your house is sucking air and threw that hole.


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## Crestliner 16 (Aug 28, 2019)

Call an Hvac company.


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## Mrfish989 (Dec 6, 2020)

Combustion air for water heater 

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## Gamekeeper (Oct 9, 2015)

Mrfish989 said:


> Combustion air for water heater
> 
> Sent from my moto e6 using Michigan Sportsman mobile app


I don’t think there’s any doubt about what it is.

But I do think the homeowner needs to understand how it works, and why his home needs it.


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## stickman1978 (Sep 15, 2011)

Crestliner 16 said:


> Call an Hvac company.


Was hoping someone on here could help. Just seems redundant that there are two make up air vents.


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## Matty Patty (Oct 9, 2019)

stickman1978 said:


> Was hoping someone on here could help. Just seems redundant that there are two make up air vents.


Maybe think of it this way instead of being redundant. 

Make up air you are paying money to "condition" via the heat exchanger (winter time / natural or propane Gass and electric blower motor) or Air conditioning evaporator coil (summer time / electric condensing unit outside and electric blower motor) 

This will add "conditioned/payed for" fresh air into the living space to make it more comfortable for the occupants. 

And helps with things like sick building syndrome, stagnic air being recirculated, humidity levels, new tight home builds etc. 

Vs. the combustion air intake which is "Free air" not conditioned who's soul purpose is to add oxygen to later be burned by atmospheric combustion appliances (Furnace / Hot water tank) 

In the diagram below the red arrows are payed for conditioned fresh air for the occupants of the living space.

The green cash symbols are free air "oxygen" from outside of the living space (not conditioned) who's sole purpose is to be used by the furnace or hot water tank for combustion.

Without the combustion air intake you would be paying money for "conditioned" make up air ONLY to turn around and use it for oxygen to complete the combustion cycle. 

Hopefully that makes some sense and helps. I'm really trying here! Lol









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## Luv2hunteup (Mar 22, 2003)

For whatever reason both my furnaces have two MUA ducts. Maybe your place had a different furnace at one time.


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## Lucky Dog (Jul 4, 2004)

That is absolutely a glory hole.


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## stickman1978 (Sep 15, 2011)

Matty Patty said:


> Maybe think of it this way instead of being redundant.
> 
> Make up air you are paying money to "condition" via the heat exchanger (winter time / natural or propane Gass and electric blower motor) or Air conditioning evaporator coil (summer time / electric condensing unit outside and electric blower motor)
> 
> ...


Ok. Thank you I appreciate the response.
It is making more sense. My exerience was the make up air to the furnace was the only air needed. Thought MUA was used for cumbustion also.


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## KingHingeCut (Oct 15, 2020)

Code requires a 4" duct into the return plenum and a 4" duct for combustion air. Probably makes your basement freezing cold.


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## TrailMarker (Dec 8, 2012)

Lucky Dog said:


> That is absolutely a glory hole.


sounds like you’re an opportunist ventureist


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## TrailMarker (Dec 8, 2012)

KingHingeCut said:


> Code requires a 4" duct into the return plenum and a 4" duct for combustion air. Probably makes your basement freezing cold.


cold and low on radon


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## Crestliner 16 (Aug 28, 2019)

I wasn't being a wise guy when I suggested that you talk to an Hvac company. To me it's just a hole that may have served a purpose at one time. But as I see it, a hole that let's cold air and vermin in. I don't claim to be an expert in Hvac,and yet you're asking people on here for a real explanation.


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## 98885 (Jan 18, 2015)

I believe it's an addition air intake source for possibly the hot water heater pilot. When I built a new home in 1997, my hot water heater pilot light kept going out. Turned out I didn't have enough oxygen in that space to keep it going. We added a 3" pvc pipe out the side wall of the basement wall allowing more air. Problem solved. Could be that was an issue in that house as well.


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## 98885 (Jan 18, 2015)

stickman1978 said:


> Just trying to figure out if we should plug with insulation or not. We are getting makeup air already.


If you have pilots on the furnace or water heater in that mechanical room, see if they stay lit after plugging that vent. If they do not, you have your answer. If you don't have pilots anymore due to those items being newer and have electronic ignition, eliminate the extra outside air.


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## stickman1978 (Sep 15, 2011)

Crestliner 16 said:


> I wasn't being a wise guy when I suggested that you talk to an Hvac company. To me it's just a hole that may have served a purpose at one time. But as I see it, a hole that let's cold air and vermin in. I don't claim to be an expert in Hvac,and yet you're asking people on here for a real explanation.


All good. When ever one posts on here or any other social media I understand there will always be a wide spectrum of answers. One just has to sift through them all.

Have gotten some very good advice on here and YouTube. Actually just saved my son a trip to the Auto shop. Car was in limp mode for some reason. Check engine light was on and wouldn't go over 25 mile an hour. Got on YouTube. Watched a few videos. Tried the turn on accessories mode hold down the break pedal for 20 seconds. This apparently reset the accelerator modual and off we went.


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## 98885 (Jan 18, 2015)

stickman1978 said:


> All good. When ever one posts on here or any other social media I understand there will always be a wide spectrum of answers. One just has to sift through them all.
> 
> Have got some very good advice on here and YouTube. Actually just saved my son a trip to the Auto shop. Car was in limp mode for some reason. Check engine light was on and wouldn't go over 25 mile an hour. Got on YouTube. Watched a few videos. Tried the turn on accessories mode hold down the break pedal for 20 seconds. This apparently reset the accelerator modual and off we went.


It's always good to get a wide variance of answers to get some ideas of what may be the issue. You tube is definitely a "Go Too" place for trouble shooting a problem.


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## brushbuster (Nov 9, 2009)

MEL said:


> Was / is there a basement bathroom? Basement bath vent fan


Looks like someone vented something there that either got flagged by inspector or no longer used.


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## Petronius (Oct 13, 2010)

Hole for a basement periscope.


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## BumpRacerX (Dec 31, 2009)

That's where you're supposed to run the feed down for the gimp.


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## Crestliner 16 (Aug 28, 2019)

I would try some of the suggestions. Just might be an answer. If not you can plug it up. And if so you should at least put some screen over it to keep out unwanted pests.


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## Wasman2. (Jan 13, 2018)

Side gig, supplement your income. Put the g room back in.


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## grapestomper (Jan 9, 2012)

There is no way it should be open like that whatever it is. 
If it was mine I would plug it.


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## Walleyze247 (Mar 20, 2009)

I have a gas, power vented water heater. I have an open vent in my mechanical room to compensate for the air it removes from the room. It was required when we built the home, circa 2004


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## Crestliner 16 (Aug 28, 2019)

Is this just a Michigan code ? I have never heard of this in Ohio. We a waste vent that has to be x amount of length above the roof and a furnace vent above the roof.


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## Old Whaler (Sep 11, 2010)

I think this is what it's supposed to look like on the outside:


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## Walleyze247 (Mar 20, 2009)

My water heater vents via pvc to the outside. This vent is for fresh air to compensate for what it draws from the room. My furnace has its own feeds.


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## TrailMarker (Dec 8, 2012)

I noticed a water line next to the opening, seems like the cold breeze could potentially freeze the line


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