<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">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. During construction, my general contractor just had a cheap 20” x 25" x <b class="">1” </b>filter in there that seemed to work just fine. I checked the installation instructions for the furnace and there are no specifications for the filters, other than that they need to be changed regularly, which is getting pretty expensive. Is there any reason I couldn’t just use 1” filters, which are less than half the price? Maybe even put two of them in the box, a good one first to catch most of the dust and a cheap one like the contractor used as a secondary one. It is a snug fit and I don’t think there is any danger of them tipping, but two would make it impossible.<div class=""><br class=""></div><div class="">Thanks,</div><div class="">Jim</div></body></html>