<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div dir="ltr"><br></div><div dir="ltr"><br><blockquote type="cite">On Dec 13, 2021, at 16:20, Jim Stone <1789alpine@gmail.com> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><meta http-equiv="Content-Type" content="text/html; charset=utf-8">The company that installed my HVAC system a few years ago used a filter box on the return line that takes 20” x 25" x<b class=""> 4”</b> filters, which is an unusual, and thus expensive, size - filters generally run about $25 each - that is not readily available other than online. </div></blockquote><div><br></div><div>Is there a reason you aren’t using a washable, reusable filter? That’s what four inch housings are for, usually. </div><div><br></div><div>If you install two 1” filters, put the cheap on as the prefilter. </div></body></html>