Heater BTU vs. CFM

Rank: Amateur
I have a payne PG9MAB forced hot air natural gas furnace. It's rated at 80000 BTU. Is it safe for me to assume that it will deliver 800cfm?
I'm sizing duct and adding branches to match 800cfm. Am I on the right track?
thanks Jerome
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NO

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No, the CFM required is dependent on the required temp rise. An 8K out furnace with a 50F temp rise needs to move around 1500 cfm.

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Jerome;
The Payne PG9MAB you mention produces about 72,000 bth/hr depending on your altitude [derate above 2,000 feet - see instructions] - the 80,000 models comes in several air delivery sizes, namely 3-Ton; 4-ton; and 5-ton. Which one do you have? Will there be air conditioning? Or just heating. Will you be running this unit on medium, low medium or low? Will you be sizing your duct [including return] for .5" w.c. or more, or less? BTW: each furnace has a different temperature rise according to the air delivery. What is your target rise?
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"jeorme" < snipped-for-privacy@ptd.net> wrote in message
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Altitude = 600ft Air Delivery Size = cant find Air Conditioning = No Medium, LM, Low = I don't know is this something I set up? What does this mean? .5" w.c. or more, or less = I don't know what this means? What is your target rise? = 30F to 70F The heater says, "40 to 70" on the data plate.
My plan was to run ductboard off the plenum and tap off vertically to registers on the first floor (640sq ft.). Then, the 3 rooms on the second floor: 117, 160 and 54 square feet get vertical pipes (6", 8" and 5"). I figured with 800cfm I'd just keep subtracting with each register I connected or keep adding on the first floor to bleed off 800cfm.
This is the first home project I've undertaken where a sneaking feeling that I might be totally off base keeps creeping in.
I appreciate the interest and advice. Jerome

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the potential to be a VERY expensive mistake regarding operating expenses and damage to a mis-applied system. You might want to consider an expert for help Bubba

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But he still has not answered the MAIN question........

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jeorme wrote:

http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_systems.html - udarrell

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PROPER A/C UNIT & DUCTWORK Sizing is over 70% of Operating Efficiency
http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_systems.html
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