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Old 01-02-2007, 05:12 PM   #1
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Replacing My Furnace, few simple questions


My 20+ year old gas furnace finally took a dive. I got a few quotes from local HVAC companies for a replacement and installation and nearly soiled my pants.$3,000-$5,000 was the average.
I dont have that kind of money, and I am a pure DIY.

My uncle said he got his furnace from the industrial supply company Grainger.
So I shopped around and bought an 80% efficiency Dayton unit (made by York) that was properly sized my house and its heat loss. it was about $600.
This is a single story house with the furnace in the garage.

My main issue of concern:
Flue: currently the old furnace blew its Flue gasses up the chimney, its about a 6" diameter sheet metal pipe that goes into the brickwork. There are flakes of corrosion that fall out when you jar the flue pipe, so I am thinking the chimney liner is no good.
Should I bother with trying to reline the chimney, or should I just run a 3" PVC flue pipe from the new furnace up into the attic, then horizontal out the side of the house?
The gas water heater also has a flue pipe, and sits right next to the furnace. I would like to have it join with the furnace flue and then just worry about plumbing one flue to the outside.
Does the water heater Flue need to be sheet metal? If so, can I join it to the PVC furnace flue pipe?

Just looking for general Flue guidance. I think I can handle the rest of the aspects of the installation without too much trouble.

thanks

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Old 01-02-2007, 05:36 PM   #2
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Replacing My Furnace, few simple questions


Hi compression

There are some things I need clarified or to clarify before I go into this. You said you bought a 80% york furnace. I have not seen a 80% furnace to date that you can use pvc pipe on. If it is a 90% furnace you will have to run a seperate flue for both the water heater and the furnace. The 90% furnace will use pvc while the water heater should be a 3" type B double wall. Hope this helps, let us know if you need any more answers.

Good luck
Rusty

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Old 01-02-2007, 05:46 PM   #3
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Replacing My Furnace, few simple questions


its definitely 80%, which means hotter exhaust gasses, right? So PVC is not even an option?
So, I need to do a 3" metal pipe flue, up into the attic (about 5 feet) then over (about 10 feet) to the side of the house and outside. can I join the water heater flue pipe into this one? i imagine if i did, I would need to up the size to 4"?

Last edited by compression; 01-02-2007 at 05:49 PM.
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Old 01-02-2007, 05:57 PM   #4
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Replacing My Furnace, few simple questions


Hi compression

You can tie the water heater to the furnace flue. You will want to use a 5" flue pipe back to a 5" tee. Then you will reduce at the tee for the water heater, it should be a 3" and you will reduce at the tee for the furnace which should be a 4". All of the flue pipe should be type B double wall. Let us know if you need any more answers.

Good luck
Rusty
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Old 01-02-2007, 06:03 PM   #5
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Replacing My Furnace, few simple questions


thanks for the help so far!

I think I am just going to run the flue into the attic then out the side of the house. I dont want to mess with that old chimney....

When the flue pipe passes through the ceiling of the garage, then through the side of the house, what do I use around the pipe at those locations to protect against the hot pipe? Will my local lowes or home depot have the parts to do this?

Also, the furnace exhaust outlet is 3", should I step that up to 4" as soon as possible? or just run a 3" until it meets up with the water heater flue and do the 5" on out from there?
thanks again!
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Old 01-02-2007, 08:19 PM   #6
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Replacing My Furnace, few simple questions


Hi compression

If the furnace BTU's are above 60,000 you definately will want to go to a 4" just off the furnace. It looks like you pretty much have the jest of the rest of it. Lowes should have the type B vent pipe and parts you will need. But be ready, this stuff aint cheap. As far as going through the ceiling you will want no less than 1" clearance around the pipe. You can get escutcheons to cover the oversized hole. And you can get thimbles to finish the ouside wall.

Good luck
Rusty
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Old 01-31-2007, 03:42 PM   #7
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Replacing My Furnace, few simple questions


Just for archival purposes....

The installation went great. I found a local do-it-yourself HVAC place. They answered all my questions and had everything I needed. they stocked all the double-wall flue piping and fittings I needed. They even made my custom sheet metal manifolds with my measurements. Everything went smoothly and this first timer got it done in one day.
I found the company in the Yellow pages under "sheetmetal"

It looks very professional. I have been inspecting all my friends/families furnaces (for my own learning) and my job looks just as good if not better than most of them.

Moral of the story?
Find a local DIY sheetmal/HVAC place!
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Old 02-02-2007, 02:29 PM   #8
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Replacing My Furnace, few simple questions


My concern would be that simply going out the side of the house with a chmney..powerventers are used when venting horizontaly. how did you exit the house with the bvent chimny pipe?
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Old 02-02-2007, 08:03 PM   #9
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Quote:
Originally Posted by coolmen View Post
My concern would be that simply going out the side of the house with a chmney..powerventers are used when venting horizontaly. how did you exit the house with the bvent chimny pipe?
I ended up going straight up through the attic and through the roof. put in new flashing and a vent cap. I capped off the chimney vent pipe so I wouldnt get draft into the garage.
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Old 02-03-2007, 02:58 PM   #10
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Replacing My Furnace, few simple questions


I just moved into a house with a gas furnace, and was surprised to feel how much heat is going up the flue. I realize this is for ventilation purposes, but I wonder if I'm losing too much heat up the chimney and not out to the rooms. Is that possible?
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Old 02-03-2007, 06:00 PM   #11
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Quote:
Originally Posted by aljanney View Post
I just moved into a house with a gas furnace, and was surprised to feel how much heat is going up the flue. I realize this is for ventilation purposes, but I wonder if I'm losing too much heat up the chimney and not out to the rooms. Is that possible?
The higher the efficiency of the furnace, the less heat is lost in the flue. High efficiency furnaces (90%+) have very low flue gas temperatures, and are also much more expensive.

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