Customer
Actual vs nominal dizes
I had bought filters at Home Depot that oddly didn’t fit my furnace, despite being correct size. I emailed Purolator who educated me about nominal vs. actual filter sizes. I ordered the Purolator brand (you don’t generally see Purolator brand on big box stores). The filters arrived in about a week and fit perfectly. The only downside is you have to buy a minimum dozen filters.

