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Our next task is to list each room and the square footage as well as the cfm of air required per room.  Living Room 300 square feet x .6 cfm/sq. ft. =180 cfm of air required.

Now our next task is to locate the supply diffusers. In our example house we figure one supply diffuser at a 6" take off size is capable of up to 100 cfm. If you can stick to the 6" size because it makes it a lot easier.

So we need 1200 cfm and that means we need a minimum of 12 diffusers. Remember that word MINIMUM! I always like to place more than the minimum amount of diffusers so as I'm placing the diffusers I look at what areas are going to need the most air. Naturally the kitchen will need more air than any other part of the house because of the heat generated for cooking. As you see I've spotted or placed 16 diffusers rather than the 12 Minimum.

Whoa! Wait a minute! Where did that number 100 cfm per ton come from? Did you just pull that out of the sky or what???

That's where I use a duct calculator or a software design program. We have duct calculators available with explanation sheets for $10.00. In the next paragraph I'll be explaining how to use the duct calculator or any duct software program.

Now that I have my diffusers located, we can begin to design the duct system. Real simple! What's the easiest and shortest route to get from the Furnace to the diffusers using the least amount of elbows? I've laid out the main plenum, the trunks and then the take offs. In the next drawing I've laid out the duct system to connect the system together.

Now we are ready to size the main plenum. We use the equal friction method to size the furnace. The equal friction method is the easiest and most accurate way to determine duct sizing for non-complex duct systems. To size a duct we use what we call an air duct calculator. You will need this for sizing your duct system.

Now our next task is to locate the supply diffusers. In our example house we figure one supply diffuser at a 6" take off size is capable of up to 100 cfm. If you can stick to the 6" size because it makes it a lot easier.

So we need 1200 cfm and that means we need a minimum of 12 diffusers. Remember that word MINIMUM! I always like to place more than the minimum amount of diffusers so as I'm placing the diffusers I look at what areas are going to need the most air. Naturally the kitchen will need more air than any other part of the house because of the heat generated for cooking. As you see I've spotted or placed 16 diffusers rather than the 12 Minimum.

Whoa! Wait a minute! Where did that number 100 cfm per ton come from? Did you just pull that out of the sky or what???

That's where I use a duct calculator or a software design program. We have duct calculators available with explanation sheets for $10.00. In the next paragraph I'll be explaining how to use the duct calculator or any duct software program.

Now that I have my diffusers located, we can begin to design the duct system. Real simple! What's the easiest and shortest route to get from the Furnace to the diffusers using the least amount of elbows? I've laid out the main plenum, the trunks and then the take offs. In the next drawing I've laid out the duct system to connect the system together.

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