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I assume the opening going through the floor under the furnace is to draw in fresh air, right.
If this is the case and is the source of least resistance how does the furnace draw air from the rest of the house creating circulation?
In a older poorly constructed mobile there would be plenty of fresh air infiltration to create air exchange but in a tighter newer home what would happen to circulation and air quality if that vent became blocked.
Would the furnace in fact be able to operate properly without that fresh air access point.
I am simply curious as it does appear to be a rather large hole allowing cold air to enter the home especially when the furnace is not running.

You have 2 different air systems. One is for combustion the one that takes outside air in, And the other is for the heat exchange (hot /cold air). If everything is sealed right the two should not mix. Greg

What type furnace and how old is home and furnace ?



Thanks,
Robert

It's about a 5 year old Nordyne and the vent I am referring to is about 1.5 inches wide and about 12-16 inches long located directly in front of the hot air duct in the floor at the base of the furnace. It goes straight down to the space under the home.
My son has a similar vent on a 20 year old furnace that goes through the floor and opens in his basement ceiling.

Is it an older home ?



Thanks,
Robert

My home is about 35 years old and my son's, which still has it's original furnace, is about 20 years old.

Hi,

On your home:

Do you have a gas furnace ?

Where are your supply registers ? In the floor or the ceiling ?


Yours is about a 1975 and homes were different back then.

Your son's being a 1990, should not have anything like what I'm thinking. However, could be a manufacture type thing from your locality .


Old homes often had the old style way of getting combustion air from below. Some alos had the return air come into belly area and up from underneath furnace.

Usually, these are one of the two and having a newer furnace can negate their need, but not always.


Your son's could have been something else by manufacturer or someone ~thinking~ their home was missing something and adding it on IF he is not the original homeowner.

Is there a way to contact the manufacturer of the homes ?




Thanks,
Robert

My place has always had a oil furnace, vents are in the floor, definitely not return air as it connects, opens, directly to the crawl space under the home.
I am positive it must be a fresh air source for the furnace but do not believe it is required.

Not sure about my sons place but because it simply opens into his basement it doesnt really matter what it is for, in my opinion.

Hi,

Yours was most likely for combustion air for the original furnace. Main thing is to always determine what it is before closing off for safety.

Not sure what your son's is unless it is an add on.



Thanks,
Robert

Thanks for the feedback.

Hi Greg,

You're very welcome, happy to help. With yours being 5 years old, it would have the newer two pipe roof jack for combustion air and vented gas.

Floor registers means downflow so return air would be through front door panel or a grille above the furnace.

Supply air through duct in belly and up through floor registers.


IF that is the case, I see no reason or need for the vent to below home as you described.


Thanks,
Robert