Multiple filters

I’ve always been told there is no need for double filters, and can cause more problems - makes air handler work harder, etc.
Just did a house, has a central air intake inside, in a vaulted ceiling, with a washable filter inside.
There is also a disposable filter in the base of the air handler… It’s a brand-new system, just replaced in a 1991 home. I think they put in the new, and didn’t know there was a filter in the ceiling also…
My thoughts are to recommend the homeowner remove the ceiling filter. It’s not needed, plus it’s very inconvenient for the homeowner to replace regularly… thus, it won’t get replaced regularly…

I am not familiar enough with those systems…I have seem what you describe while in the south. I would make note of the double filter, which is atypical, and recommend the buyer verify the installation instructions with the qualified professional that installed it…maybe through the homeowner…in writing.

Good post I try to not box myself by telling what they need to do in cases like this in case I am wrong .

I let them know that one is sufficient.

IN this case, the system is new, and has the installer decal on it. I’m going to recommend they call him to ask about the double filter. I just wanted to get an idea if others see this. Thanks!

You want to try to extend the life of a more expensive filter with a prefilter design. If the filter that is in the air handler is a throw away you need to note it needs checked periodically for load. Fliters in the ceiling prevent you from ever having to clean the return duct work and that is the only purpose for them. This you can allow the Home Owner to decide if he wants to remove it and have the duct work cleaned by a professional on a regular basis. If the pressure across the filter is too great you will be able to check that by a HVAC technician if you so desire.

Get rid of the washable filter… It’s too small for the system.

Can you explain to us old farmers how one acquires a pressure on the negative side of a blower:shock: me thinks the word differential is a better choice of words.

One of your statements at least was correct it is considered best practice to have a return air grill with filter installed at the inlet of the return VS at the air handler to prevent dust accumulation in the duct work. I would not go so far as to say two filters in series are incorrect but it sure effects the efficiency of the unit and I always recommend just one good quality filter be used

We call it across the filter however the most tech term is differential. All factors of the filter design need to fit with the static pressure allowed with the HVAC. This is what I am recommending for those that are concerned about it now.
By design, HEPA air filters will create resistance to flow, and a high differential pressure drop will exist ** across the filter**. Most HEPA air filter manufacturers literature suggests replacement of HEPA air filters when the resistance due to dust loading has reached 2 in.wg.

I always figure that with a filter installed in a ceiling return, few homeowners will regularly drag out a ladder, climb up, and replace the filter, as opposed to walking out to the garage and replacing the one at the base of the air handler unit…

About the only time I recommend a filter be installed at the return register is: when they are floor or low wall returns and they have pets.
Use the cheapest filter available. You are only after the fur.

Next time you get a chance Stephen put a cheese cloth on a high return flush to the grill and look at it the next week. What really works well is a cheap carbon filter because as it gets loaded with skin flakes,fur,hair and dirt it changes from black to light grey. This way when you look at it you can’t help but clean it…:wink: