New old furnace for the the garage

[VTP99]

I've seen Carrier RTU'S with the in-shot burners leaking and forming puddles below the burners.
Usually on hot humid days.

[heatingman]

thank you for answering..

its has been a very long time since i ever installed an 80%, a very long time....all newer ones for the last 12 years with 90% have the coil inside opposite of the furnace being an all in one unit... the ones that was not , design spec was 12" before the return, because all was horizontal install (with anti vibration hanging from the diagonal 2x10's) ...everything else is heat pumps by popular choice

i have seen a few 90% with the evap coil directly above it with no way to properly clean the inside of the coil as maintenance...

the package units HE have a bad design as the primary tubes dont pitch back to drain the condensate that causes it to rot internally, but i will see light seam rot first....I am in a much warmer climate so most heat exchanges last 7-10 years....

the smooth tube bend heat exchanger last much longer than the ripple bend ones where i find the most amount of pinholes because the metal is stretched thin at those points

Ive never seen a combo indoor unit that is a combination gas heat with evap coil pre-built from the factory.

Everything residential here is a split system, furnace totally separate from evap coil.

Residential air handlers/electric heat furnace - sure evap in on the suction side of the blower from the factory. But never saw a gas fired version of one.

Do you have a model number of the style you are referring to?


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[Unlimited1]

Ive never seen a combo indoor unit that is a combination gas heat with evap coil pre-built from the factory.

Everything residential here is a split system, furnace totally separate from evap coil.

Residential air handlers/electric heat furnace - sure evap in on the suction side of the blower from the factory. But never saw a gas fired version of one.

Do you have a model number of the style you are referring to?


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oh geeze, it was awhile ago.....it was known as the "extended cabinet version " with your choice of coil size..the best reference i could maybe compare it to on looks would be a mobile home downflow unit nowadays....except these was "universal airflow configured" and it was always left horizontal/topflow from the factory


THERMAL ZONE CMC1-75D36N 75,000 BTU DOWNFLOW NATURAL GAS MOBILE FURNACE 95%
https://www.ebay.com/c/14015388408?iid=203076207504

i also used to install these Hydronic style air handlers in replacement of the Apollo units
https://www.alpinehomeair.com/relate...ec%20sheet.pdf

[heatingman]

oh geeze, it was awhile ago.....it was known as the "extended cabinet version " with your choice of coil size..the best reference i could maybe compare it to on looks would be a mobile home downflow unit nowadays....except these was "universal airflow configured" and it was always left horizontal/topflow from the factory


THERMAL ZONE CMC1-75D36N 75,000 BTU DOWNFLOW NATURAL GAS MOBILE FURNACE 95%
https://www.ebay.com/c/14015388408?iid=203076207504

i also used to install these Hydronic style air handlers in replacement of the Apollo units
https://www.alpinehomeair.com/relate...ec%20sheet.pdf

If a coil is going in that thermopride, it would be on the leaving side of the heater, which would be essentially the same as what I have.


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[CHAINIK]

Why the combination of single wall pipe and B-vent? Is there some reason that the draft hood connector cant go right at the inducer?

[heatingman]

Why the combination of single wall pipe and B-vent? Is there some reason that the draft hood connector cant go right at the inducer?

No, it could, its just my cheapness.

Its also the standard method here. Single wall connector to B-Vent stack.


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[mofotech]

Hey heatingman, I have a question.. with your round metal pipes how much btus will one lose if their not insulated in heating mode and if there in a un condition space lets say a open warehouse? But for only heating mode. Also how much a temp differents it may make out of vents? If i was getting 115F out of a supply vent... can it be 120F if the round pipe was well insulated?

[heatingman]

Hey heatingman, I have a question.. with your round metal pipes how much btus will one lose if their not insulated in heating mode and if there in a un condition space lets say a open warehouse? But for only heating mode. Also how much a temp differents it may make out of vents? If i was getting 115F out of a supply vent... can it be 120F if the round pipe was well insulated?

The first is easier to figure then the latter.

Heat loss is dependent on surface area and temperature difference.

But for 6” round I believe its 2.35 square feet per foot. (r x r x 3.14 x 12)/144

So to find the btu loss per foot, you need the temperature difference between the pipe and the surrounding air. And the shininess of the pipe will have some effect at reflecting the heat back in, but minimal once the pipe itself is hot.

The formula would be the same as any heat loss. I believe the R value of sheet metal is about .9 so the U value so the U value is 1.1

Q=Area in Square ft X u factor X temp diff
Assuming a 35 degree difference

2.35 x 1.1 x 35 would be 90.5 btu per lineal foot.

In 10 feet thats 900 btu assuming the duct temp is a constant which it isn’t

The amount of temperature drop across the length is dependent on amount of flow. The less flow, the more the drop as there is less energy replacing the lost energy. And I dont know off the top of my head how to calculate that. But I did find an online calculator that I will reference for you, which I have to assume is at least somewhat accurate.

https://www.wbdg.org/guides-specific...ator-air-ducts


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[mofotech]

The first is easier to figure then the latter.

Heat loss is dependent on surface area and temperature difference.

But for 6” round I believe its 2.35 square feet per foot. (2r x 3.14 x 12)/144

So to find the btu loss per foot, you need the temperature difference between the pipe and the surrounding air. And the shininess of the pipe will have some effect at reflecting the heat back in, but minimal once the pipe itself is hot.

The formula would be the same as any heat loss. I believe the R value of sheet metal is about .9 so the U value so the U value is 1.1

Q=Area in Square ft X u factor X temp diff
Assuming a 35 degree difference

2.35 x 1.1 x 35 would be 90.5 btu per lineal foot.

In 10 feet thats 900 btu assuming the duct temp is a constant which it isn’t

The amount of temperature drop across the length is dependent on amount of flow. The less flow, the more the drop as there is less energy replacing the lost energy. And I dont know off the top of my head how to calculate that. But I did find an online calculator that I will reference for you, which I have to assume is at least somewhat accurate.

https://www.wbdg.org/guides-specific...ator-air-ducts


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Awesome.. thanks for the info

[heatingman]

Awesome.. thanks for the info

No problem.

A few corrections- the pipe temp may not be the inside air temperature, so would be more accurate to go by the surface temp of the pipe.

And get rid of the U factor

So just average surface temp - surrounding air temp x area of the pipe in square feet


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[Unlimited1]

on another positive note...radiant heating and cooling if it stays exposed in the conditioned space! lol

[BaldLoonie]

Find a multimillion dollar house in our little burb and you won't find workmanship anywhere near this nice!

[heatingman]

Find a multimillion dollar house in our little burb and you won't find workmanship anywhere near this nice!

Thats a sad truth. The trades are in a race for the bottom. Especially in new construction. I do find it somewhat uplifting to see so many retrofits posted on this site that are truly professional and well crafted.


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[strogen]

Find a multimillion dollar house in our little burb and you won't find workmanship anywhere near this nice!

Yep, this is some top drawer work. Most everything in Chicagoland is tin and thinwall. But not too many jobs look like this. Nice work Heatingman!

[steelersfan1]

Nice supply duct work! Is your return temporary?? Didn't think your were supposed to be drawing your return from where the furnace is. I'm sure I'm probably missing something.

[GenesisRefrig]

Nice work on the HVAC and really nice work on the electrical. I like both high and low outlets.

Two things I’ve never heard:
“I wish this garage wasn’t so big”.
“I wish I didn’t have so many outlets”.

[heatingman]

Nice supply duct work! Is your return temporary?? Didn't think your were supposed to be drawing your return from where the furnace is. I'm sure I'm probably missing something.

Its not temporary. But that is correct in general. You dont really want the return drawing from the combustion air zone. And Id probably be tempted to write it up if I found such in a customers home. But - this is a garage, and there are no doorways between the furnace and any of the supply outlets. Also no doorways between the 2 floors. So as applied I view the combustion air issue no differently then a hanging heater.

If the furnace were in a sealed closet or even a basement for example, and the return was drawn from the same space as the combustion air, and the supply side was isolated from the furnace like you would find in a house, then that would be a potential issue for lack of combustion air.


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[CHAINIK]

I didn't think that Carrier approved side returns for downflow applications, maybe thats a newer thing. The manual I think is the right one says no.

[VTP99]

I didn't think that Carrier approved side returns for downflow applications, maybe thats a newer thing. The manual I think is the right one says no.

You know what, I believe you're correct on that 🙄

[VTP99]

Although there's no return static pressure so he's probably okay.