If you are looking for the installation of a new filter, screw open the old one and use a scale to measure the size of the furnace filter, or may find that the size is written on the specification chart of the filter. Then you can look for the same sized filter in the online stores as well as go out to purchase it offline. There are times you may find it very difficult to determine the size of your filter. The equipment which is used to measure the HVAC (Heating, Ventilation and Air Conditioning) can get a bit puzzling.
Determining the size of the furnace filter
Generally, manufacturers use the inch unit to measure their filters. 20*20*1 or 20*25*2 is one such example of it. Sometimes there comes a confusion when there is slight variation in the actual size if the filter and the measurement are written on it. It generally differs by half an inch. There are more cases of people getting the wrong sized filters because the user does not any the measurement information written on it; therefore he uses his own tools to measure the filter, which ultimately goes wrong completely.
This highly hampers the confidence and keeps you in worry throughout the time, the time from when you have placed your order with the time it has arrived, and you have fixed it in place. The manufacturers usually keep the listed measurement a little higher than the actual measurement because it will help to keep the margin of error. So it is obvious that if you have ordered a filter which is of the exact size of the size of your cabinet, it is never going to fit in there. You will have to follow the same rule in the case of determining the thickness of the furnace air filters.