Your ac contractor or engineer will determine the correct size.
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∙ 14y agoreally depends on the size of the unit but if your not sure i would go with a 20x20 or a 20x25 filterback grill..
Air return duct and filter grille size is dictated by the size of the unit (CFM) not the size of the house.
The best rule of thumb I have found is: Length X Width / 144 * 288 = Max. CFM I have used this formula to size many HVAC systems. It has always worked. For example, a 5 ton unit should have a 30x36 grille(2-18X30 filters). (30x36)/144*288=2160 max cfm. Return Air should be sized at 200 square inches per ton according to AirMate and other filter grille manufacturers to achieve 2.0 static pressure. The Return Air Duct should have an unobstructed 6 square inches per 1000 BTU of cooling.
a 4 ton unit
A 16" round flex duct will accommodate up to a 3.5 ton unit
quick down and dirty way is the size of your unit (example..4 tons) X 144= the square inches needed for the return vent size or the longer way Max air flow from unit (rated size) / 2.08 cfm/sq in= filter area needed
The grill if I recall correctly is one unit. What I mean by one unit is that the grill housing goes around the headlights / around the whole front of the vehicle. I have a 1998 Ford Expedition XLT. I ended up cutting my grill out of the housing and installing an aftermarket one in its place.
To determine the correct size breaker, you need to ensure that it is rated higher than the running amps of the unit. For a unit drawing 58 running amps, a breaker that is rated for at least 70 amps would be appropriate to provide a safety margin and prevent tripping due to overload.
The size of any unit is, by definition, 1.
There should be appx 15*-20* difference between return and supply air temps measured at the unit (not the registers).
The filter is most likely in the area of the return box. This box is usually located beneath the system. If you have a gas furnace the filter may be behind the bottom door. It is possible that you have a return filter grill which would be on the wall or in the ceiling. You must figure out how the system is getting its return air and that is the most likely place to look for the filter.
it should be well defined it should be of suitable size it should be internationally accepted it should be easily reproducable it should not be affected by the environmental conditions