The new furnace is a two stage. The burner comes on initially at a low
temperature and very slowly brings the fan speed up. If, after about 15
minutes, the desired temperature hasn't been reached it cranks up to a
higher burner temperature. Ultimate fan speed is controlled by DIP
switches which can be set by the homeowner independently for heating and
cooling. I believe there are four fixed fan speeds for top speed. Same
as the current unit but it does not have variable speed during startup
and rewiring is required to change the speeds. Furthermore cooling and
heating can't have the same top speed on the old unit. 19 years
progress in low cost electronics.
Chuck Norcutt
On 12/7/2012 11:58 AM, Mike Lazzari wrote:
> I think a major problem in updating a forced air furnace is that the
> ducting is designed for the old system. Frankly many houses I've seen
> were not designed at all rather a seat of the pants installation relying
> upon brute force. Usually the system is sized too small for the needs of
> a modern furnace. Particularly the design of the return air. Before
> investing in a new furnace have someone run the calcs on your old
> existing system to see if it also needs to be updated to move lower
> velocity air.
>
> Mike
>
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