# Furnace Venting Requirments



## jamiedolan (Sep 2, 2008)

Hello;
I have a Goodman highboy GMV 95% series furnace. We installed it about 2 years ago. All is well. 

However, due to other projects, I think I may have to move the flue vent outlet for the furnace today. It is 2" PVC. I am looking for the spec on the distance this can run / the run of bends & turns allowed. I checked the goodman site and this is all I found:

_Installer must supply one or two PVC pipes: one for combustion air (optional) and one for the fl ue outlet (required). Vent pipe must be_
_either 2” or 3” in diameter, depending upon furnace input, number of elbows, length of run and installation_​_(1 or 2 pipes)._

Anyone out there have any idea what distance I can run this vent pipe with how many bends in it?

Thanks very much
Jamie


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## Marvin Gardens (Sep 30, 2008)

I don't have the information for your furnace but I would not go longer than 40 feet with more than 20 90's...JUST KIDDING HERE,,,THAT IS FOR HVACLOVER...DON'T TAKE THIS SENTENCE AS ANYTHING BUT A JOKE.

Seriously with a 2 inch pipe no more than 5 90's at 20 feet if I remember correctly. If you have to go more than that then you will have to go with a 3 inch pipe.

Here is the problem.

There are safely mechanisms build into high efficiency furnaces. One of these mechanisms is a pressure sensor for the exhaust. If the pressure gets to high the furnace shuts down assuming that the exhaust is plugged. If you have too much back pressure in the pipe then it will shut down. The reason that it shuts down is do prevent CO from being pushed into the building. I test the pressure sensor by holding my hand over the exhaust and it shuts down right away if the pressure sensor is working.

Things that cause the pressure to build up is the total length of the pipe and the number of angles, especially 90's. It can be a combination of both length and 90's that will cause a problem. The number of 90's and length is just a rough estimate. I have seen situations where 4 90's in a 2 feet has caused enough back pressure to shut down the furnace. It was a self install and the guy didn't have a hole saw and figured that he would just use a lot of 90's. His run to the roof was only 8 feet. Once I took out the 90's an put a single pipe to the roof his furnace worked fine, (except for the t-stat hook up but I won't go into that now).


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## dac122 (Sep 5, 2008)

Your first indication you have it wrong is the furnace will not start and you may get a control module led fault blinking something about pressure switch. If you can rough fit things and do a quick test fire of the furnace that might keep you from having to redo a bunch of work.


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## kennzz05 (Nov 11, 2008)

for what its worth not saying im right but ive never seen any 90+ allow more than 4 90s in the exaust run and the longer the run the better off you are going to the 3in pipe


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## jamiedolan (Sep 2, 2008)

Marvin Gardens said:


> I don't have the information for your furnace but I would not go longer than 40 feet with more than 20 90's...JUST KIDDING HERE,,,THAT IS FOR HVACLOVER...DON'T TAKE THIS SENTENCE AS ANYTHING BUT A JOKE.
> 
> Seriously with a 2 inch pipe no more than 5 90's at 20 feet if I remember correctly. If you have to go more than that then you will have to go with a 3 inch pipe.
> 
> ...


I ended up being able to do the electrical work without having to move the pipe today. However, I deffinatly still want to get the pipe into a better location. Ideally I would like to have it exit the house about 35' from the furnace. I could use just 45's and it would be a mainly straight run. I wonder if this would work then if I used 3"..
Thank You.
Jamie


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## tk03 (Sep 30, 2008)

I would probably call goodman and ask them as it is their product. They will have all the answers.


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## Marvin Gardens (Sep 30, 2008)

jamiedolan said:


> I ended up being able to do the electrical work without having to move the pipe today. However, I deffinatly still want to get the pipe into a better location. Ideally I would like to have it exit the house about 35' from the furnace. I could use just 45's and it would be a mainly straight run. I wonder if this would work then if I used 3"..
> Thank You.
> Jamie


If you used 3" there is almost no back pressure and you could run a long ways. The problem is slope. You have to have 1/4" drop per foot to keep condensation from building up. That's a 9" incline over 35 feet.


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## kennzz05 (Nov 11, 2008)

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## hvaclover (Oct 2, 2008)

Refer to the following table for applicable length, elbows, and
pipe diameter for construction of the vent/flue pipe system of a
non-direct vent installation. In addition to the vent/flue pipe, a
single 90° elbow should be secured to the combustion air intake
to prevent inadvertent blockage. The tee used in the vent/flue
termination must be included when determining the number of
elbows in the piping system.
Pipe
Size (4)
(inc.) 2 3 4 5 6 7 8
045_3 2 68 65 62 59 56 53 50
070_3 2 68 65 62 59 56 53 50
070_4 2 46 43 40
2 16 13 10
3 68 65 62 59 56 53 50
090_5 3 68 65 62 59 56 53 50
115_5 3 68 65 62 59 56 53 50
Non-Direct Vent (Single Pipe)
Maximum Allow able Length of Vent/Flue Pipe (f t) (1) (2)
Models Number of Elbow s (3) (5)
(kBtu_Tons
)
090_4
Not Recommended
1) One 90° elbow should be secured to the combustion air intake connection.
2) Minimum requirement for each vent pipe is five (5) feet in length and
one elbow/tee.
3) Tees and/or elbows used in the vent/flue termination must be included
when determining the number of elbows in the piping system.
4) 3” diameter pipe can be used in place of 2” diameter pipe.
5) Increased Clearance Configurations using (2) 45 deg. Long Sweep
elbows should be considered equivalent to one 90 deg. elbow.
VENT/FLUE PIPE TERMINATIONS
The vent/flue pipe may terminate vertically, as through a roof, or
horizontally, as through an outside wall.
Vertical vent/flue pipe terminations should be as shown in the
following figure. Refer to Section IX, Vent/Flue Pipe and Combustion
Air Pipe - Termination Locations for details concerning
location restrictions. The penetration of the vent through the roof
must be sealed tight with proper flashing such as is used with a
plastic plumbing vent.
Horizontal vent/flue pipe terminations should be as shown in the
following figure. Refer to Section IX, Vent/Flue Pipe and Combustion
Air Pipe - Termination Locations for details concerning location
restrictions. A 2 3/8” diameter wall penetration is required for
2” diameter pipe while a 3 1/2” diameter hole is required for 3”
diameter pipe. To secure the pipe passing through the wall and
prohibit damage to piping connections, a coupling should be installed
on either side of the wall and solvent cemented to a length
of pipe connecting the two couplings. The length of pipe should
be the wall thickness plus the depth of the socket fittings to be
installed on the inside and outside of the wall. The wall penetration
should be sealed with silicone caulking material.
In a basement installation, the vent/flue pipe can be run between
joist spaces. If the vent pipe must go below a joist and then up
into the last joist space to penetrate the header, two 45° elbows
should be used to reach the header rather than two 90° elbows.
Counterflow units.
Remove plastic plug from alternate combustion air intake
location. Relocate and install plug in standard air intake
location (basepan). Plug the remaining hole in the blower
deck with the plastic plug included in the drain kit bag.
4. Upflow and Counterflow units.
With the gasket facing the cabinet side panel, and the
flange’s flat spot facing forward, secure the combustion
air intake coupling to the cabinet using the screws removed


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## pipefitter636 (Nov 1, 2008)

hvaclover said:


> Refer to the following table for applicable length, elbows, and
> pipe diameter for construction of the vent/flue pipe system of a
> non-direct vent installation. In addition to the vent/flue pipe, a
> single 90° elbow should be secured to the combustion air intake
> ...


I think you just gave me a headache


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