So I'm installing a furnace in my pole barn. I have a 100K input furnace with a 20x20 supply opening. Upflow design with a 20x20 plenum and a 12x20 trunk to supply my ducts. Simple straight forward shop heat. I have the furnace positioned and from the top of furnace to floor where the trunk line will lay is 10" up. Then a 12" trunk height. My question is how much height should I leave in the plenum? I was thinking 2" seems right. Gives some room for error and connections from plenum to trunk. But I could go more or less. Any thoughts? This is just my homeshop, I'm doing it myself. No Sched D or other. But I would like to make the most out of what I'm doing.
Plenum Height?
- Thread starter RonRock
- Start date
fitter30
Well-known member
12x20 is for 1250 cfm Not knowing what your output is 1300 cfm @60° rise Formula is
Cfm x 1.08x delta t = btu's
2" above is fine. Using prefab duct from a box store? If a shop is making the plenum turning vanes would help or they can make a sweeping L
If you were in the future thinking of ac duct would be to small. AC is 400 cfm per ton.
Cfm x 1.08x delta t = btu's
2" above is fine. Using prefab duct from a box store? If a shop is making the plenum turning vanes would help or they can make a sweeping L
If you were in the future thinking of ac duct would be to small. AC is 400 cfm per ton.
Thanks, Yes I am using a Plenum that I bought from Menards. I will never add AC to this shop. Not that I wouldn't like AC, but it would just be too costly to run. And I like to have the OHD's open.
My unit is a Ruud 96% 100k input 2 Stage. The manual has a chart on air flow based on various External Static Pressure,
0.1 ESP = 1,561 CFM
0.4 = 1,436
0.5 = 1,394
0.9 = 1,186
I don't see any listed Btu output.
I plan to have 2 - 6" runs pretty much right off the plenum. then 7 -8" runs. 24 foot trunk. 12 x 20 reduced to 12 x 16 after 2 -6" and 2 -8" runs. 12 foot to reduction in trunk size.
Any thoughts would be appreciated. I enjoy the work, but never had to figure out the ductwork. I did what they tell me.
My unit is a Ruud 96% 100k input 2 Stage. The manual has a chart on air flow based on various External Static Pressure,
0.1 ESP = 1,561 CFM
0.4 = 1,436
0.5 = 1,394
0.9 = 1,186
I don't see any listed Btu output.
I plan to have 2 - 6" runs pretty much right off the plenum. then 7 -8" runs. 24 foot trunk. 12 x 20 reduced to 12 x 16 after 2 -6" and 2 -8" runs. 12 foot to reduction in trunk size.
Any thoughts would be appreciated. I enjoy the work, but never had to figure out the ductwork. I did what they tell me.