cboley4

I'm just getting started on a large, low-budget rehab project on a farmhouse that was built before they knew what modern heating was. For the past thirty or forty years it's been heated (??) by two propane wall furnaces and a bathroom space heater. Less than half the house is heated directly, and while tearing out ugly plaster in three rooms, I plan to install 3x12 ducts between the joists for the installation of a new heating/cooling system. So far I can't find much info on the volume of ductwork needed to insure adequate airflow. Anything would be better than what it has now, but I don't want to pay for energy that isn't being used efficiently. Any suggestions?

glennjanie

Hello Cboley and Welcome to the Forum:
HVAC contractors use a duct calculator to size their jobs. It is like a little slide rule that gives instant answers. I worked for a National Distributor of HVAC-R for 3 years in the early 90's but, somehow, I have lost my calculator.
The best I remember a 3 X 12 duct will not carry over 100 cfm; same as a 6" round duct.
Unico, Inc. makes a system that is well suited for older homes.
They start with a high velocity/ high pressure unit and use an 8" square duct for a trunk line, a hose that looks like vacum cleaner hose, silencer adapters at the terimnis and use a register that is no larger than a porcelain bulb fixture. They are very convenient to snake through walls, ceilings and floors. I have talked to customers who had them and they were very well satisfied.
Glenn

asbestos

you are getting into the black arts as far as sizing the furnace and such also . take some time, you will NOT want to do this again

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