When the supplier installed our modern heat pump as well as A/C unit, they didn’t tell us what size air filters to use in the machine. The first time I received a message from the thermostat to change the air filter, I was ready to go abruptly. I grabbed a screwdriver as well as removed the outer lid. I looked everywhere on the air filter, although I couldn’t find the size at all. I thought it was weird that the air filter didn’t have any writing, although I guess the Heating as well as Air Conditioning insulation supplier must get them directly from the factory. I tried not to worry, as well as I grabbed a tape measure, pencil, as well as small pad of paper. I measure the air filter from one side to the other as well as back again. The measurements that I got were 21 in long by 20 in wide. I didn’t want to wait to order the part online, especially when the local hardware claimed to have 37 air filters. I jumped in the truck as well as drove directly to the store. I stopped to grab some dinner, although I made my way to the store in record time. I searched through the aisles, until I located the location where all of the home air filter supplies are kept. They had about 50 or 60 weird types of air filters, as well as I had to search for several minutes, before locating my particular size, luckily, the air filter was reasonably priced, as well as I was back home in no time. I locationd the modern air filter into the machine, as well as it almost disappeared. Somehow, I purchased the wrong size or measured in officially, because the air filter was way too small.