return grille size times 2 gives u the amount of cfms u are getting out of the return air grille, i.e. 10x10x2=200cfms...
If you are looking for an easy method that is not based in scientific data try this: Heating requirement is the same as cooling. To calculate Btu needed to cool look at the furnace for input Btu then multipy that by effeciency of unit. Now think about the coldest day the furnace will provide okay heating such as 5 degrees outside and 68 degrees inside. Subtract those and you have 63 degrees. If you heating Btu was 80000 input and 80% efficient, you need 64000 btu to heat 63 degrees. Do similar math to hottest day and desired inside cool temperature. Maybe 103 degrees outside and 72 degrees inside. That is 31 degrees difference. Use heat math of 64000 Btu for 63 degree which is very roughly 1000 Btu per degree. Apply that to cooling and it's roughly 31000 Btu, or around 2-1/2 ton cooling. Please don't bark at me about the basic nature of my math-I thought I would explain this as a method to start or get an idea. There is a method that accounts for all factors but no way could I explain it. Also, if using electric heat your btu will be about 4.5 per watt and no efficiency applies. The watts can be found on the inside of the furnace above the blower.
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
There are going to be allot of varying opinions on this one but it's fairly simple to get in a good ball park. You want between 600 to 800 feet per minute of air flow so you need to know the CFM of your air handler and then you can calculate it this way. Ftcube /min divide by Ft / Min = Ft square. At 1200 CFM for a flow rate of 800 Ft/min you get a result of 1.5 square feet which is 216 square inches. If you divide by 8 for the prefab 8 inch duct you need a 27 inch wide dimension or 16 X 13.5. Good luck on your project.
air resistance
A "gas furnace" is called a furnace, an "electric furnace" is called an Air Handler
The furnace or air handling unit in the house.
Furnace filters control the amount of particles that pass out of the furnace and into the house. They are essentially the first line of defence in keeping the air in your home clean.
Replacing the furnace filter can improve air flow in your furnace by allowing air to pass through more easily. This helps the furnace operate more efficiently and can improve air quality in your home.
Is there a flame in the furnace. Precisely where is this air coming from and how strong is it?
the arrow points in the direction of air flow.
What type of furnace do you have?electric
it's the same as the furnace filter. the air conditioner runs through the furnace to push he cold air. change your furnace filter and you are changing the air filter on the air conditioner
The furnace air filter is typically located near the air intake of the furnace, which is usually found in the return air duct or near the blower motor. It is important to regularly check and replace the filter to ensure proper functioning of the furnace.
Air flows in a furnace from the return ducts into the furnace, where it is heated and then pushed out through the supply ducts to heat the home.
Regularly replacing the air filter in a furnace helps improve air quality, increase energy efficiency, and extend the lifespan of the furnace.
Your furnace may be blowing cold air and then hot air intermittently due to a malfunctioning thermostat, a clogged air filter, or issues with the furnace's ignition system. It is recommended to have a professional HVAC technician inspect and repair the furnace to resolve the issue.