I have a gas forced hot air heating system. There is a large filter that is installed in the area where the system's duct work is against the furnace itself.

Shouldn't that filter 'slide' into an area that allows very little, if any air, from the basement to get into the system itself?

My filter has a large gap all around it so air from the basement gets 'pulled' into the furnace during operation.

My thoughts are that is not how this is supposed to work.

Air returning to the furnace to be reheated should come from the rooms that are heated by this furnace.

Am I correct in my thinking?

 

Ductwork is not perfectly sealed so air will get into the system from the basement through seams and within the filter area but NOT after the filter. Unfiltered air getting into the air handler can cause dust and debris to enter causing the system to run inefficiently at beat and breakdown at worst.

One simple solution may be to buy larger filters that cover the entire space.

BTW, if I'm misunderstanding your concern and your issue is the temperature of return air, don't be concerned. Return air ducts aren't usually insulated and and the return air temperature will be impacted by the basement.

 

Than you for your response Tony. My concern is that the air in the system should all go to the rooms by any 'feeder' duct, and then return from the rooms to be re-heated, through the return duct system. I do not think that any air from my basement should get by the large return filter also. Am I wrong to think that is so?

 

I attached a picture of the filter setup. That area should have a 'filter box' in that area IMHO




Like this unit: https://www.homedepot.com/p/MaxxAir-...filter%7D%3Aqu

 

As long as the filter is pulled against the furnace side it should do the job.
On my old furnace I actually has a piece of coat hanger looped over the blower motor to pull the filter against the furnace as they flopped all over the place.. More to keep dust from the utility room out of the ducts/blower than to seal out air.

The amount of air pulled from the basement will be minimal.
Look at the square inches of return duct compared to the square inches of basement air getting in.
It will be a minuscule percentage.

 

Yes..... one would think so but I've rarely seen one in an installation. Usually the filter mount is fabricated on-site and leaves little to be desired.

 

Yes. It's generally referred to as a filter rack or housing. The cost of one should be under $100 unless you need something special or custom, which doesn't appear to be the case.

Take several good photos and measurements then visit HD, Lowes, or a HVAC supply place. They should have what you need and be able to give basic information on the installation.

Alternatively, you can hire a handyman for the install. I suspect the job may be too small for large HVAC contractors.

Finally, depending on what's on the other side, you would substantially reduce the basement airflow by propping a piece of sheet metal against the opening that can be moved to insert the filter.

 

I am quite sure that the feed side of the system is also non-insulated metal duct work. It was installed when the home was built in 1970 or so. They have also installed a dropped ceiling right up against the duct work. Needless to say getting a peek at everything has not been possible thus far. I have to rely on others to check things out for me now. I have stage 4 COPD and I am on O2 24/7. So, stairs/ladders and I do not get along very well. Now with the Holidays coming up it can wait!

 

Usually when the air handler/furnace is located in a climate controlled area..... there is no insulation.
There isn't much benefit to insulating the ductwork in a heat only system as the hot air rises.
Insulating the supply ducts is more advantageous on a heating/cooling system to keep the cold in.

 

I'm not certain this is correct. The system operates like drinking soda with a straw. If the straw is a tiny distance from the soda, the straw will not work and no soda will be pulled up.

Air from the return ducts isn't mechanically forced into the system, it is sucked in, which obviously works fine as long as the system is closed. In this case, the system would certainly suck air from a few feet of the return duct into the system due to the pressure imbalance but that pressure differential would dissipate quickly. It's quite likely the remaining pressure would be insufficient to suck air all the way from the living area so, eventually much of the air would have to come from the basement.

Simply stated, at some point the return duct has to be too far away to function properly (like the straw) and while this may not be too far away it certainly could be.

 

Comments are correct, when the furnace was installed they would have built a filter box to fit between the return duct and furnace.

All you need are the filter size, the width of the gap, size of the furnace box, it's opening size and the duct size and it's opening size.

Make a few calls and locate a smaller HVAC company that will fabricate the insert, they will make it for you and save a house call.

It will then simply slide in the gap and a few sheet metal screws your all set!