Where is the filter for the Central AIr?

[Sir.M.Messervy]

Hi, I've been in my house for a year, I looked inside all of the interior air intakes for my central air system, and none of them seem to have a filter. I was in the crawl space yesterday and saw what look like used filters, left by prefvious owner. Do all Central air systems have filters? If the filters is not in the intakes where are they? The machinery of central air system is in the crawl space, is the filter located in this part of the system? Thanks.

[Eric in North TX]

Mine is on the intake side of the air handler (squirrel cage fan), but mine is an a closet in the house. Seem odd that they would force going to the crawl space to change filters, but who knows what the installer was thinking. If you find it there and don't like that, you could always change out the intake grills to ones that take filters, & just leave the one in the unit out.

[DerbyDad03]

re: you could always change out the intake grills to ones that take filters

Replacing the single filter with multiple filters at the intakes could restrict air flow to the system making it work harder or be less efficient.

The OP might want to get an on-site professional opinion before going down that path.

If you've been there a year and don't know when the system was inspected last, it might make sense to schedule a check-up. When you call to make the appointment, tell them you want to talk about changing the filter layout and that you want to make sure that they send out a knowledgable service rep.

[Joseph Meehan]

...

More likely it would reduce the restriction since it would be equivalent to using a larger filter. Just make sure the original filer is removed and that any opening at that point is sealed.

[DerbyDad03]

What am I missing?

Let's say your system has a 20" x 20" opening (400 square inches) with a single filter causing some amount of restriction. This restriction could be measured on a per inch basis, determined by the filter material.

In this same system, ahead of the single filter, you've got 10 intakes, all measuring 10" x 5" (500 square inches) unrestricted by a filter.

Now you pull the single 400 square inch filter and replace it with ten

50 square inch filters, each of whom restrict the same amount of air per square inch.

Haven't you restricted 100 additional square inches of opening - 500 instead of 400?

[Chris Hill]

Yep, that's generally where the filter is located. It will be where the intake air goes into the unit.

[BobK207]

The pressure drop across each of the multiple intake filters is lower than the pressure drop across the single filter.

Take the example to the extreme case.

Case one replace a single 20x20 with 10 ea 10x5's 400 sq in of filter gets replaced by 500 sq in of filter

Case two replace the single 20x20 with 100ea 10x5 400 sq in of filter gets replaced by 5000 sq in of filter

Now you're "restricting" 12x the area....will this help or choke off the flow?

having a larger filter on your shop vac doesn't restrict the flow more, a larger filter provides less restriction. Tape over half of the filter....the vac will struggle.

Add a filter in parallel & the vac will not work as hard even though you've "restricted" twice the area.

It's the concept of resistors in parallel.

cheers Bob

[BobK207]

The pressure drop across each of the multiple intake filters is lower than the pressure drop across the single filter.

Take the example to the extreme case.

Case one replace a single 20x20 with 10 ea 10x5's 400 sq in of filter gets replaced by 500 sq in of filter

Case two replace the single 20x20 with 100ea 10x5 400 sq in of filter gets replaced by 5000 sq in of filter

Now you're "restricting" 12x the area....will this help or choke off the flow?

having a larger filter on your shop vac doesn't restrict the flow more, a larger filter provides less restriction. Tape over half of the filter....the vac will struggle.

Add a filter in parallel & the vac will not work as hard even though you've "restricted" twice the area.

It's the concept of resistors in parallel.

cheers Bob

[Red Green]

[e-mail] wrote in news:fec4bbe1-557e-4e1f-866c- [e-mail]:

SInce you went to the extreme of looking in the crawl space, I imagine you looked hard here but...

...in one closet unit in an apt I saw it slid in a narrow slot like a card. Once inserted, all you would see is one of the narrow edges.

[Cheri]

filter

imagine you

Mine is in the side of the unit and slides into a slot as you say. It has a metal piece that slides down over the slot after the filter is inserted, so it's hard to see. I looked for it for awhile before finding it.

Cheri