"Arnie Goetchius" wrote in message
A local Plumbing contractor says the following:
“In the case of a central heating and air conditioning system, closing off
has the same effect as a dirty air filter. It simply restricts airflow.
systems are designed to heat the whole home and are sized accordingly.
off a section of airflow increases the air pressure in the system, in turn
increasing the amount of duct work leakage."
"A more energy efficient way to control individual temperatures in unused
is by using a ductless heating and cooling mini split systems that are
on the wall and wired using a simple wiring process to an outdoor unit. No
are used so installation doesn’t take much time at all. Ductless heating and
cooling mini split systems are a flexible solution.”
My question: Is closing the ducts to three unused bedrooms and an unused
bathroom a bad idea and it won’t save any money on the gas bill?
The way that I look at is this way--Heating systems use a centrifugal fan
(and when up to speed) runs at constant speed. It has a characteristic
operating curve of delta P (pressure rise) vs air flow and as the air flow
demand increases there is a slight drop (called Droop) in Delta P. The
change in fan pressure usually is not very significant unless the flow
demand is very high (very low system resistance). The duct work also has a
system characteristic of Pressure Drop vs air flow. Plot the two operating
systems (fan and ductwork) on the same curve and where they intersect is the
system operating point--a fan pressure rise and flow.. Change the system
resistance (close of some of the vents for example) and you will get a new
operating point because the duct work characteristics have changed. Same
fan speed but at a slightly different (higher) Delta P and at some reduced
air flow. Unless the system changes are extreme, I don't see any
significant operating or system problems. I don't think that closing off a
few registers can be considered extreme.
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