PDA

View Full Version : Calculating cfm

Dust2505
03-25-2012, 02:29 PM
Does anyone have a affordable solution for calculating cfm for a/c units?

skidoox800
03-25-2012, 02:33 PM
Calculating CFM for indoor blower?

Total External Static..
Use blower chart in paperwork that came with furnace to see what CFM you are pushing with that static pressure at which fan speed.

Very easy, just use your manometer..

Dust2505
03-25-2012, 03:04 PM
What do you do if charts is not with heater?

HJ Controls
03-25-2012, 03:13 PM
go online and get the paperwork for that unit.

garyed
03-25-2012, 04:22 PM
If you've got electric heat you can use the temp. rise method.

skidoox800
03-25-2012, 05:10 PM
Can always call whoever makes the unit, speak with tech support and they can tell you your cfm with your total external static pressure, and which blower speed you are on. Get that info first, and obviously Model/Serial of air handler. Type of coil is helpful also.

heatingman
03-25-2012, 06:04 PM
as long as you have the ability to run in heat mode.

output btu / temp rise * 1.08 = cfm

Run the heat in the cooling speed.

If electric heat, then kw * 3.414 / temp rise * 1.08 = cfm

run the fan in cooling speed.

example:

Furnace output = input * efficiency

100,000 btu in * .8 (80%)

80,000 btu output furnace / 50 deg rise * 1.08 = 1481 cfm

80,000 btu output furnace / 60 deg rise * 1.08 = 1234 cfm

So the higher the rise, the less the flow.

Dust2505
03-25-2012, 08:26 PM
Heating man thank you for the breakdown that simplifies it big time.

heatingman
03-26-2012, 09:20 PM
Anytime.