Yet another furnace upgrade question...
 

I live in MD and have a 30+ year old gas furnace that soon needs
replacement. BGE is the local company and their man recommended a two-stage
Carrier unit exactly matching my old one's BTU rating. In the last 2 years
we have added insulation, replaced all doors, (particularly a sliding door
that might as well have well been a hole in the wall!), and put in really
great windows.
With these upgrades, do we have to match BTU for BTU with the old and new
units? From some other posts here, I wonder if it's necessary. Also, can
anyone give me some feedback on BGEs estimates and savings with upgrades?
Gerry

Yet another furnace upgrade question...
 

that's quite a lot of difference in heat load. you should get a new
calculation done.
the new furnace can no doubt be significantly smaller.

bill

"Gerry Gardiner" wrote in message
. ..
I live in MD and have a 30+ year old gas furnace that soon needs
replacement. BGE is the local company and their man recommended a
two-stage
Carrier unit exactly matching my old one's BTU rating. In the last 2 years
we have added insulation, replaced all doors, (particularly a sliding door
that might as well have well been a hole in the wall!), and put in really
great windows.
With these upgrades, do we have to match BTU for BTU with the old and new
units? From some other posts here, I wonder if it's necessary. Also, can
anyone give me some feedback on BGEs estimates and savings with upgrades?
Gerry

Yet another furnace upgrade question...
 

Im sure a much smaller unit will work , you didnt even refer to Output
btu, output btu will be much more with a 90%+ Carrier unit. Your sales
guy is taking the typical lazy ass way out. First you may be oversized
now, but with more insulation and more efficient units there are 3
reasons to demand to see a written load calc. Never replace till you get
the load calculation.

Yet another furnace upgrade question...
 

The guy is most likely just a salesman who gets paid a percentage of the
sale. I doubt if he did a heat loss calculation. Call around for more
estimates until you find someone you can trust.

"Gerry Gardiner" wrote in message
. ..
I live in MD and have a 30+ year old gas furnace that soon needs
replacement. BGE is the local company and their man recommended a
two-stage
Carrier unit exactly matching my old one's BTU rating. In the last 2 years
we have added insulation, replaced all doors, (particularly a sliding door
that might as well have well been a hole in the wall!), and put in really
great windows.
With these upgrades, do we have to match BTU for BTU with the old and new
units? From some other posts here, I wonder if it's necessary. Also, can
anyone give me some feedback on BGEs estimates and savings with upgrades?
Gerry

Yet another furnace upgrade question...
 

Then "their man" is an incompetent or a liar. Didn't do load calc.

Tell BGE "no good, try again." And why.

DAGS on this; it is NOT news.

J

Yet another furnace upgrade question...
 

I thought furnace BTU ratings were output BTU or Bonnet BTU....


BTU per Hour actually.

And to the OP... look at the duty cycle (% of on time to off time) of
your present furnace on the coldest days. If it is say 50% and you get
a new furncace that is 50% BTU rating then it will run 100% of the time
i.e. continuously on the coldest day...

Using the operation of your present furnace is probably the most
accurate way to judge your BTU requirements.

Mark

Yet another furnace upgrade question...
 

Mark wrote:

I thought furnace BTU ratings were output BTU or Bonnet BTU....


BTU per Hour actually.

And to the OP... look at the duty cycle (% of on time to off time) of
your present furnace on the coldest days. If it is say 50% and you get
a new furncace that is 50% BTU rating then it will run 100% of the time
i.e. continuously on the coldest day...

Using the operation of your present furnace is probably the most
accurate way to judge your BTU requirements.

Mark


That's correct. And you don't need to wait for the coldest day
to make measurements. Pick a day when it's overcast, so there
is little heat gain from the sun. Let system stabilize for
say, 4 hours. Measure duty cycle. Now, if the outdoor temp
has been steady 35F and indoor is 70F, the diff is 35 degrees.

Take the furnace "output" BTU/Hr rating and multiply by
the %hour running time. That gives you BTU/Hr.
Divide that by 35 to give BTU/Hr/Degree diff.

If the design temp (minimum) you want is, say, 10 below zero
multiply by 85 (70 to -10) to give the BTU/Hr required.
Add another 10% overcapacity if desired.

Jim

Yet another furnace upgrade question...
 

On 2006-02-02, Bubba wrote:

Holy Crap, Jim. Ive never heard such silly **** out of you in my
life. The guy needs a Manual J load calculation done on his
home. PERIOD! That's THE ONLY way to know. Bubba

Why should a theoretical estimate be better than a direct measurement?

Cheers, Wayne

Yet another furnace upgrade question...
 

"Why should a theoretical estimate be better than a direct measurement?


Cheers, Wayne "

That's exactly what I was thinking. Any inaccuracies in back
calculating it from the duty cycle of
his existing furnace is likely to be less than a theoretical
calculation.