The unit in question is Goodman GMV9509050XBA gas furnace (95% eff.,
90,000 BTU.)
It says in the Installation Instructions (page 7, Location Requirements
& Considerations) that the following must be observed:

"The temperature of the return air entering the furnace is between 55F
and 100F when the furnace is heating."

I am curious why the 55F requirement. I mean, when I'm not in the
house, I would like to set the temp as low as possible in order to save
on my heating bill. I think I could otherwise set it as low as 45-50F
and still keep the water pipes from freezing. But I wonder why I'm not
supposed to go below 55F. What could happen? Could the unit get damaged
and why?

Thanks

P.S. I'm in the Denver, CO area - 5,300 ft altitude, if that matters.

wrote:
The unit in question is Goodman GMV9509050XBA gas furnace (95% eff.,
90,000 BTU.)
It says in the Installation Instructions (page 7, Location Requirements
& Considerations) that the following must be observed:

"The temperature of the return air entering the furnace is between 55F
and 100F when the furnace is heating."

I am curious why the 55F requirement. I mean, when I'm not in the
house, I would like to set the temp as low as possible in order to save
on my heating bill. I think I could otherwise set it as low as 45-50F
and still keep the water pipes from freezing. But I wonder why I'm not
supposed to go below 55F. What could happen? Could the unit get damaged
and why?

Thanks

P.S. I'm in the Denver, CO area - 5,300 ft altitude, if that matters.

Hi,
I am just guessing. If return air temp. is to low it may not produce
warm enough air. Air is passing thru the heat exchanger at constant
speed and think law of physics.

On Fri, 19 Jan 2007 05:59:45 GMT, Tony Hwang wrote:

wrote:
The unit in question is Goodman GMV9509050XBA gas furnace (95% eff.,
90,000 BTU.)
It says in the Installation Instructions (page 7, Location Requirements
& Considerations) that the following must be observed:

"The temperature of the return air entering the furnace is between 55F
and 100F when the furnace is heating."

I am curious why the 55F requirement. I mean, when I'm not in the
house, I would like to set the temp as low as possible in order to save
on my heating bill. I think I could otherwise set it as low as 45-50F
and still keep the water pipes from freezing. But I wonder why I'm not
supposed to go below 55F. What could happen? Could the unit get damaged
and why?

Thanks

P.S. I'm in the Denver, CO area - 5,300 ft altitude, if that matters.

Hi,
I am just guessing. If return air temp. is to low it may not produce
warm enough air. Air is passing thru the heat exchanger at constant
speed and think law of physics.


Blow me.



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'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
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Tony Hwang posted for all of us...

I am just guessing.

That is ALL you are capable of; the subject does not matter. Go guess back in
a.h.r you might find a sucker there.
--
Tekkie Don't bother to thank me, I do this as a public service.

On 18 Jan 2007 21:12:17 -0800, wrote:

The unit in question is Goodman GMV9509050XBA gas furnace (95% eff.,
90,000 BTU.)
It says in the Installation Instructions (page 7, Location Requirements
& Considerations) that the following must be observed:

"The temperature of the return air entering the furnace is between 55F
and 100F when the furnace is heating."

I am curious why the 55F requirement. I mean, when I'm not in the
house, I would like to set the temp as low as possible in order to save
on my heating bill. I think I could otherwise set it as low as 45-50F
and still keep the water pipes from freezing. But I wonder why I'm not
supposed to go below 55F. What could happen? Could the unit get damaged
and why?

Thanks

P.S. I'm in the Denver, CO area - 5,300 ft altitude, if that matters.

Blow me.



--
Click here every day to feed an animal that needs you today !!!
http://www.theanimalrescuesite.com/

Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/

well lewts say the home is 40 degrees, and moisture is accumulating.
pretty quick the temp should rise, and the moisture go away

perhaps he should call the manufacturer?

long term would more likely be a problem

wrote:
well lewts say the home is 40 degrees, and moisture is accumulating.
pretty quick the temp should rise, and the moisture go away

perhaps he should call the manufacturer?

long term would more likely be a problem


Interesting question. One thing I've observed on my gas forced air
system is that if the house gets very cold, when the furnace first
starts up, the blower will come on for a min or two, then shut off
again. This is because the cold air causes the temp in the furnace to
drop enough that the temp switch turns off the blower. Maybe that is
one consideration. But it shouldn't be harmful, just somewhat
wasteful of electricity. In my case, if the house is down at 45, I
just put the blower on manual for awhile, until the house gets up to 55
or so.

On 18 Jan 2007 21:12:17 -0800, wrote:

The unit in question is Goodman GMV9509050XBA gas furnace (95% eff.,
90,000 BTU.)
It says in the Installation Instructions (page 7, Location Requirements
& Considerations) that the following must be observed:

"The temperature of the return air entering the furnace is between 55F
and 100F when the furnace is heating."

I am curious why the 55F requirement. I mean, when I'm not in the
house, I would like to set the temp as low as possible in order to save
on my heating bill. I think I could otherwise set it as low as 45-50F
and still keep the water pipes from freezing. But I wonder why I'm not
supposed to go below 55F. What could happen? Could the unit get damaged
and why?

Thanks

P.S. I'm in the Denver, CO area - 5,300 ft altitude, if that matters.


Now are you reading that right? Is that a statement of general
operation, or an actual requirement?

tom @ www.YourMoneySavingTips.com

It is my understanding that if the return air temperature is too low
the
heat exchanger can be "shocked"--that is to say it may expand and
contract
beyond design limits and fail.

Any metal will expand and contract with change of temperature
but I do not believe that this problem occurs in low temp.
residential furnaces however anything is possible
Dido

"Redcrosse" wrote in message
ups.com...
It is my understanding that if the return air temperature is too low
the
heat exchanger can be "shocked"--that is to say it may expand and
contract
beyond design limits and fail.

I am told by experts in the field that one of several ways that
high-efficiency furnaces squeeze more BTU's from their fuels is by
using thinner and thinner heat exchangers that naturally have tighter
tolerances for expansion and contraction. Old coal fired furnaces had
cast iron heat exchangers that could and did last for a very long time.
Most "cracked heat exchangers" in those appliances seem to have been a
salesman's way of getting a customer to buy . . . not an actual crack.
Modern furnaces with crimped stainless steel heat exchangers are often
projected to have a life of 15 years +/-.




AKS wrote:
Any metal will expand and contract with change of temperature
but I do not believe that this problem occurs in low temp.
residential furnaces however anything is possible
Dido

"Redcrosse" wrote in message
ups.com...
It is my understanding that if the return air temperature is too low
the
heat exchanger can be "shocked"--that is to say it may expand and
contract
beyond design limits and fail.

On 22 Jan 2007 06:23:03 -0800, "Edward R. Voytovich"
wrote:

I am told by experts in the field that one of several ways that
high-efficiency furnaces squeeze more BTU's from their fuels is by
using thinner and thinner heat exchangers

This seems like one of the false efficiencies, for the most part.
Although it would take a few seconds, even a minute maybe longer to
heat a thick heat exchanger wall, once it was heated all the way
through, it would be just as efficient as a thin one.

Then at the end of the cycle, there would be more heat left over,
which would disperse, some warming the circulating air which would
continue to be circulated by the fan (until the low-limit thermostat
switched the fan off) and the rest would eventually heat the basement
a little bit, or wherever the furnace was. In the case of my
basement, I need a bit of heat there in the winter, and there is a
heating duct, and the furnace radiates is a small amount but probably
needed for my comfort.

If the furnace were in the garage, well one normally goes to a garage
even less than a basement, but doesn;t the whole furnace radiate heat,
not just the rather small amount in even a thick heat exchanger wall.

that naturally have tighter
tolerances for expansion and contraction. Old coal fired furnaces had
cast iron heat exchangers that could and did last for a very long time.
Most "cracked heat exchangers" in those appliances seem to have been a
salesman's way of getting a customer to buy . . . not an actual crack.
Modern furnaces with crimped stainless steel heat exchangers are often
projected to have a life of 15 years +/-.

Oy.




AKS wrote:
Any metal will expand and contract with change of temperature
but I do not believe that this problem occurs in low temp.
residential furnaces however anything is possible
Dido

"Redcrosse" wrote in message
ups.com...
It is my understanding that if the return air temperature is too low
the
heat exchanger can be "shocked"--that is to say it may expand and
contract
beyond design limits and fail.

mm wrote:
On 22 Jan 2007 06:23:03 -0800, "Edward R. Voytovich"
wrote:

I am told by experts in the field that one of several ways that
high-efficiency furnaces squeeze more BTU's from their fuels is by
using thinner and thinner heat exchangers

This seems like one of the false efficiencies, for the most part.
Although it would take a few seconds, even a minute maybe longer to
heat a thick heat exchanger wall, once it was heated all the way
through, it would be just as efficient as a thin one.

That simply isn't true. The heat is going to transfer more
effectively across the thinner material. The thickness of the metal
provides a resistance to heat flow, just as thicker insulation, wood,
or anything else would.





Then at the end of the cycle, there would be more heat left over,
which would disperse, some warming the circulating air which would
continue to be circulated by the fan (until the low-limit thermostat
switched the fan off) and the rest would eventually heat the basement
a little bit, or wherever the furnace was. In the case of my
basement, I need a bit of heat there in the winter, and there is a
heating duct, and the furnace radiates is a small amount but probably
needed for my comfort.

If the furnace were in the garage, well one normally goes to a garage
even less than a basement, but doesn;t the whole furnace radiate heat,
not just the rather small amount in even a thick heat exchanger wall.

that naturally have tighter
tolerances for expansion and contraction. Old coal fired furnaces had
cast iron heat exchangers that could and did last for a very long time.
Most "cracked heat exchangers" in those appliances seem to have been a
salesman's way of getting a customer to buy . . . not an actual crack.
Modern furnaces with crimped stainless steel heat exchangers are often
projected to have a life of 15 years +/-.

Oy.




AKS wrote:
Any metal will expand and contract with change of temperature
but I do not believe that this problem occurs in low temp.
residential furnaces however anything is possible
Dido

"Redcrosse" wrote in message
ups.com...
It is my understanding that if the return air temperature is too low
the
heat exchanger can be "shocked"--that is to say it may expand and
contract
beyond design limits and fail.

Well, the verdict is in. I called a Goodman authorized HVAC
dealer/contractor (in Denver Metro), and their technician told me that
the reason that return air temp must not be less than 55F is because of
the possibility of excess condensation.

BTW, I first called the Goodman hotline, but they told me that, for
liability reasons, they didn't provide tech support directly to
individuals. However, they told me to call one of their authorized
dealers with any questions. They gave me three names, and I called one
of them.

Cheers.


On Jan 18, 10:12 pm, wrote:
The unit in question is Goodman GMV9509050XBA gas furnace (95% eff.,
90,000 BTU.)
It says in the Installation Instructions (page 7, Location Requirements
& Considerations) that the following must be observed:

"The temperature of the return air entering the furnace is between 55F
and 100F when the furnace is heating."

I am curious why the 55F requirement. I mean, when I'm not in the
house, I would like to set the temp as low as possible in order to save
on my heating bill. I think I could otherwise set it as low as 45-50F
and still keep the water pipes from freezing. But I wonder why I'm not
supposed to go below 55F. What could happen? Could the unit get damaged
and why?

Thanks

P.S. I'm in the Denver, CO area - 5,300 ft altitude, if that matters.