Custom size HVAC filters?

[CFIT]

My house has the a/c-furnace on the roof. Inside there are two air returns with filters. Unfortunately, the filters that are required are custom sizes and can't be found at big box stores. In the past I've ordered custom filters online. They are well made and fit right in but cost $65 a filter. I have also hacked up cheap filters from Lowes, mounted them in cardboard and given them the duct tape treatment. Not a pretty solution and by the time I'm finished the expense of ordering online doesn't seem so bad.

Any advice on this or pointers to reasonably priced custom filters?

Thanks.

[livesoft]

I bought BoAir filters online. They are permanent and washable, so I have not bought any other filters since. That is, it was a one-time charge. They can make just about any size you want. Washing is easy and quick. I usually use a pressure washer.

[nominalBob]

I don't know if these are cheaper because you didn't state the size, but try:
http://www.filters-now.com/

[sport]

What would it cost to modify your system so it can use standard size filters? This would be a one-time expense.

[Teague]

What would it cost to modify your system so it can use standard size filters? This would be a one-time expense.

I was wondering that as well. Which brings us to the $64 question. OP, are you saying the filters are actually way up on the roof as part of the unit? Or (more likely I think) are they located behind grilles in the living area?

[mnvalue]

What size filter are you looking for? When answering this question, please note if you're giving nominal or actual size. If you have both, give both please.

Here's a place I recommend:
https://4qualityair.com/custom_orders.php

By any chance, does the filter "hole" have reinforcements (metal bars) every few inches, or could you add them, such that you could use unreinforced filter material? If so, that company has DustLok filter material in big rolls and can cut it to any size you want. For example, I use that for my air exchanger; the metal slats in the exchanger core keep the filter from being "sucked in" anywhere, so it can use unreinforced filters.

[CFIT]

The filters are in the ceiling on the main floor of the house. The a/c-furnace is up on the roof.

I hadn't thought of it before, but having the ductwork changed to accommodate standard sized filters would have another benefit. One of the metal grates that sits in front of (actually below, since it is in the ceiling) the filters is screwed into the drywall of the ceiling with metal screws. This makes it a pain to removed the grate when I change the filter plus I expect that the holes in the drywall will eventually give out. Replacing that would make things much easier.

Thanks for the advice and help.

[Teague]

Ok, now that we know what you have, changing the return filter box should not be very involved. Bigger (more surface area) is better, up to a point. There should be no need to change any ducting, assuming it was done correctly in the first place. Make sure to properly seal with mastic and HVAC tape, or if hiring the job out, make sure the installer does so.