your going to get 800 cfm through a 20x20. Its the gross square inches divided by 2
There are 400 cfm in 1 ton
Air return duct and filter grille size is dictated by the size of the unit (CFM) not the size of the house.
1600 cfm
You need 350 to 400 cfm per ton (12,000 btu) of cooling. So, divide your cfm by 400. For example, a 1200 cfm blower on an air handler could handler up to 3 tons. All calculations depend on your duct being the proper size for the equipment.
Well, darling, CFM stands for cubic feet per minute, while CMH stands for cubic meters per hour. So, the relationship between the two is that 1 CFM is equal to approximately 1.699 CMH. It's like comparing apples to oranges, but hey, they both measure the flow of air, just in different units.
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For a 3.5-ton AC unit, the return air grill should typically be sized to allow for adequate airflow. A general guideline is to allow about 400-450 CFM (cubic feet per minute) of airflow per ton of cooling. Therefore, for a 3.5-ton unit, you would want a return grill that can accommodate around 1,400 to 1,575 CFM. It's important to consult with an HVAC professional for precise sizing based on your specific system and home layout.
The size of the return air grill depends on the size of the forced air fan. The return air grid to reduce noise should be 5 to 8 times the size of the fan outlet. A 36000 btu heating system often has between a 500 to 1500 CFM fan the outlets on these fans are often between 30 and 80 square inches so the grid should be between 150 and 600 square inches (depending on the fan), the bigger you can fit the better. If you can fit it I'd put in a 12 x36 grill (432 sq in) but a 12 x 24" (288 sq inch)grill should work well too.
return grille size times 2 gives u the amount of cfms u are getting out of the return air grille, i.e. 10x10x2=200cfms...
Return air vents in each room (none in bath or restrooms) sized for the amount of cfm needed for that specific room are best but if this is not possible then pick a central location and return vent should be sized for total cfm required of house.
There are 400 cfm in 1 ton
Air return duct and filter grille size is dictated by the size of the unit (CFM) not the size of the house.
1 ton A/C have 400 CFM
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.
The recommended return air duct size for optimal HVAC system performance is typically 1 square inch per 1 CFM (cubic feet per minute) of air flow.
To calculate sensible heat, you can use the formula: Sensible Heat (BTU/hr) = 1.08 x CFM x Temperature Difference (°F). Just multiply the CFM value by 1.08 and then by the temperature difference in Fahrenheit to get the sensible heat in BTU per hour.
~ 1000 cfm