On 2005-10-07, Joseph Meehan wrote:

Sorry not that easy. You need to do a manual D. I suggest you also
should do a manual J first. These are mathematical calculations
based on your home and HVAC equipment.

For the inquiring reader, do the calculations (heating only) go in the
following way?

Calculate the heat loss of the entire structure given the dimensions
and construction details. Choose a furnace whose capacity equals the
heat loss on the coldest day of the year. Break the heat loss down
room by room.

The furnace will specify a given flow rate at a given pressure drop.
Divide the total flow rate among the rooms proportional to the heat
loss for each room. Lay out the return and supply ducting, and
determine the flow rate through each duct segment. Choose acceptable
pressure drops for each duct segment (representing fittings by their
equivalent lengths), so that the end to end total pressure drop from
any return grill to any supply outlet never exceeds the furnace
specification pressure drop (often 0.5" wc?). Now the minimum cross
sectional profile of each duct segment can be determined from the
total pressure drop allowed for that segment, the length of the
segment, the flow rate through that segment, and a guideline for the
maximum linear velocity of the air in the segment to avoid excessive
noise.

Is that basically how it goes? Are these reasonable maximum linear
flow rates: register 250 FPM, supply branch and return trunk 500 FPM,
supply trunk 750 FPM? For a gas furnace or a hydronic furnace, how
does one determine the appropriate air temperature for the pressure
drop calculations?

Thanks, Wayne