DIYbanter - View Single Post - gas furnace register temperature question

Todd H.

writes:
Lately I had been noticing that the temperature of the "heated" air
coming out of my gas furnace was barely above room temperature, 75
degrees by my infrared thermometer. Filter is nearly new, flame is a
perfect blue.

Turns out that the problem was I'd opened up the registers to a couple
of rooms, and the "redumbdant" register in the living room. After I
closed the registers again, the temperature of the heated air shot up
to 110+ degrees at the furnace.

Now, my gut is telling me that this furnace is undersized for the house
if I can't have airflow to more than one register in the living room,
one in the breezeway and one in the main hallway without the register
temperatures dropping to barely-above-ambient. Any expert opinions on
this? House is 1300sq ft, furnace is 64,000 BTU, location is Rochester,
NY. Former owners were snowbirds and the furnace never had to do more
than keep the house at 50 over the winter.

Not enough information to judge the size of the furnace. 75F is
pretty pathetic though. But can you trust that measurement?

As for load/sizing, only an HVAC guy on site looking at your house's
layout, the ductwork, the efficiency of the furnace (which you don't
mention), and a blower door for good measure to judge infiltration
would be able to say with any certainty. Based on square footage
though, it doesn't sound so bad.

Have you ruled out duct leakage on that run?

--
Todd H.
http://toddh.net/