Is the house comfortable with the furnace running this way? *Thats* what
matters most!


"Mike" wrote in message
news:7A2bh.45$hn.19@edtnps82...

"dpb" wrote in message
ups.com...

Mike wrote:
This summer, I upgraded my walls to R20, attic to R40, replaced metal
single
windows with double low-e argon vinyl, replaced all wood doors with
insulated steel, air sealed the house and replaced a 30 year old 120k
gas
furnace with a 75k condensing unit. The old furnace used to run every 5
out
of 15 mins at 0C, now it runs 10-15 mins every 3-4 hours. Something
doesn't
seem right here as my neighbors runs 2-3 times per hour and it's a 100k
furnace in approx the same sized house with similar insulation (maybe
20%
less) I have my tstat set to +/- .5C and CPH disabled.

Don't follow the question (if there is one?). What doesn't seem
"right"?

I see a former case of running 1/3-rd the time, now only about
1/16.8-th of the time (using mid-points of on time and interval given).
That seems pretty good to me. It seems to be taking 2-3X the "on"
time to raise the temperature from "on" to "off" with something under
2/3-rds the capacity of previous (assuming same efficiency which was
probably also worse for older unit) so that also seems quite
reasonable.

Trying to then do something w/ the neighbor's "data" w/o any more
factual basis than this seems futile.

So, I'm at a loss as to what you're asking/expecting...


Old furnace was 65% AFUE steady state, much less on average, new is 92%.

The heatloss rate seems far too low (slow), most tstats have a CPH setting
whereas my cycles are PER DAY!

Maybe the problem is that the furnace btu output is too high for the rate
of heat loss. I did calculate a loss of 40k at -5C so I'm about 50%
oversized which should be ok.