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Posted by m Ransley on December 16, 2005, 10:09 am
By my spec sheet for Infinity, and im a homeowner only , a 60000
infinity out putting 57000 on high could be right for you, but you will
only know after a load calc and your units apx present output. Any
future insulating upgrades should also be considered now.
Only one Carrier Infinity or Bryant [same] is 96+%, the smallest least
sold unit, the 040-14, 37000 out put btu. The rest are 94.1 they just
added apx 20lb more metal to the exchangers on the 040. A BS marketing
ploy for advertising only as they could have done this for all the
units, but they save 20$ a unit, just more marketing BS to learn about.
Comfort is even heat oversizing wont help.
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Posted by mm on December 17, 2005, 5:21 am
wrote:
>Why in the world would you want to go to a larger size??
>Was the old furnace not keeping up?
>Are you adding on to the house?
>You said the old furnace was twenty years old, was it a 90% furnace?
>If it was an 80% and was heating the house well, you could probably go
>SMALLER!!
Is that really true?? Say his old one was 80% When his old one was
rated at 80000 wasn't that AFTER they deducted the 20% loss of
heating power.
Don't they rate the furnace on output and not on how much fuel they
burn? I have no experience with this, but that's what I would do.
I'm sure they assume the furance is clean and well adjusted when they
rate it at 80,000, but I don't think they would rate it at anything
other than 80% efficent if that is what it was.
(Or maybe they don't assume anything Perhaps they rate the furnace by
measuring it's output???. Again, I don't know. This is a question.)
>You do not want to over size a furnace. For the best in fuel efficiency you
>want the furnace to size the furnace to run constantly at the coldest days
>of the year. Over sizing the furnace will cause shorter run times and higher
>gas bills.
>Here in North Dakota we take out high BTU furnaces all the time and install
>smaller units. .One in particular we took out a 100,000 BTU Lenox and put in
>a 60,000 BTU Ruud mod furnace and it heats the house fine. I just replaced
>the furnace in my dad's house and put in a 75,000 BTU, 2400 square foot
>home. In my home I removed a 80,000 BTU and put in a 60,000 BTU Ruud mod. I
>would have gone smaller yet, but Ruud does not build a mod smaller than the
>60,000 BTU.
>Greg
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Posted by Greg O on December 17, 2005, 9:09 am
> I'm sure they assume the furance is clean and well adjusted when they
> rate it at 80,000, but I don't think they would rate it at anything
> other than 80% efficent if that is what it was.
> (Or maybe they don't assume anything Perhaps they rate the furnace by
> measuring it's output???. Again, I don't know. This is a question.)
I have never seen furnaces rated on output BTU, there may be a rating on the
label on the furnace that lists both. If I go to the wholesaler and ask for
a furnace I ask for input BTU, not output.
Greg
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Posted by m Ransley on December 16, 2005, 9:46 am
If he didnt show you the load calc I bet he didn`t do one. I don`t think
you can do it without writing it out, and you should demand a copy. If
80000 worked at your coldest days keeping you at 70f without running
24x7 then 100000 is much more than you need or want An 80000 btu unit ,
your old unit, say its 80% efficient put out 64000 btu, but it may be
much less, 60% efficient, poorly sized ducts, dirty heat exchanger, AC
coil, burner not running right etc etc. so it could be 48000 or less
output for example, mine was 50%. An 80000 btu infinity at 94.1% actual
[not 96] is 49000 on low fire and 75000 high fire btu, so depending on
what your unit really outputs and an honest load calc in writing, an
80000 infinity could be way oversized since it is more efficient. A
100000 infinity is 94.1% efficient not 96, outputs 94000 high 61000 low
fire btu. Oversize and you won`t be as comfortable if you consider it
goes to high fire after a few minutes in standard settings, it will heat
you faster unevenly. I went from 100000 btu to 47-74000, finally I got a
written load calc it was 50000 btu, I heat a bit uneven and am oversized
as I never need my second stage even at -20f with 30 mph winds. My
second stage is good for when I come home from set back temps. But I
will go smaller on my next unit soon. You need to learn more on when the
second stage is used, 1st stage should be lower for milder days with
second needed only when it can`t keep up, unfortunatly I think Carrier
comes to second after like 5 minutes, but im not sure. Oversizing is
common.
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Posted by mm on December 17, 2005, 5:24 am
On Fri, 16 Dec 2005 08:46:39 -0600, ransley@webtv.net (m Ransley)
wrote:
>If he didnt show you the load calc I bet he didn`t do one. I don`t think
>you can do it without writing it out, and you should demand a copy. If
>80000 worked at your coldest days keeping you at 70f without running
>24x7 then 100000 is much more than you need or want An 80000 btu unit ,
>your old unit, say its 80% efficient put out 64000 btu, but it may be
Really? Then I guess I would be wrong. Sorry.
>much less, 60% efficient, poorly sized ducts, dirty heat exchanger, AC
>coil, burner not running right etc etc. so it could be 48000 or less
>output for example, mine was 50%. An 80000 btu infinity at 94.1% actual
>[not 96] is 49000 on low fire and 75000 high fire btu, so depending on
>what your unit really outputs and an honest load calc in writing, an
>80000 infinity could be way oversized since it is more efficient. A
>100000 infinity is 94.1% efficient not 96, outputs 94000 high 61000 low
>fire btu. Oversize and you won`t be as comfortable if you consider it
>goes to high fire after a few minutes in standard settings, it will heat
>you faster unevenly. I went from 100000 btu to 47-74000, finally I got a
>written load calc it was 50000 btu, I heat a bit uneven and am oversized
>as I never need my second stage even at -20f with 30 mph winds. My
>second stage is good for when I come home from set back temps. But I
>will go smaller on my next unit soon. You need to learn more on when the
>second stage is used, 1st stage should be lower for milder days with
>second needed only when it can`t keep up, unfortunatly I think Carrier
>comes to second after like 5 minutes, but im not sure. Oversizing is
>common.
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>Was the old furnace not keeping up?
>Are you adding on to the house?
>You said the old furnace was twenty years old, was it a 90% furnace?
>If it was an 80% and was heating the house well, you could probably go
>SMALLER!!