Venting high eff. gas furnace through the wall.

Prince1 · 10-20-2008, 09:07 PM

I am installing a 95% gas furnace. Wondering if I can run exhaust out one side of house and intake through the other. As I understand the combustion air may be terminated under a deck, but vent may not. That is my delima. They would be sloped 1/4" / ft and be basically the same hgt as far as atmospheric pressure goes. Can anyone help? Thanks.

Prince1 · 10-21-2008, 08:26 AM

The only reason I ask this is because all the diagrams I have looked at seem to show a min of 3" apart and max of 24" apart. I guess I don't understand that and wondering if anyone knew more about it. Thanks.

Marvin Gardens · 10-21-2008, 11:37 AM

Yes you can do that. I have done that in really tight places. One had to have the vent go up a chimney that was real tight.

You can even terminate the intake inside the house but I don't recommend that although I have seen it done.

hvac122 · 10-21-2008, 04:00 PM

The reason that the manufactures don't want them on different sides of the house is because of the pressure differences that will occur and may cause intermintent unit lockouts. I would highly suggest you follow the manufactures installation manual on this.

hvaclover · 10-21-2008, 06:31 PM

Not a good idea for the following reasons:

The pressure zones are are completely different from side of the home to the other because of air press differences and air currents.

All current production 95% have a two port pressure switch that sense this diff in the vent and combustion air pipes and would cause the the press switch to lock out the furnace burners.

Marvin Gardens · 10-21-2008, 06:45 PM

I just installed an Armstrong 95% and they state that you can vent in different places. They say that the intake can be inside and the exhaust outside.

Now that is a pressure difference. Not a big one but there is a difference in pressure especially when the wind is blowing.

I was going to do an inside intake but the energytrust.org says to get their rebate of $200 I have to have the intake outside.

The one I vented up a chimney and did the intake out the back is working fine.

Where the pressure switch comes into play is if the pressure in the exhaust gets too high, then it will shut down. This assumes that the vent is blocked. In fact to test them I just put my hand over the exhaust and it shuts down.

hvaclover · 10-21-2008, 07:35 PM

Quote:

Originally Posted by Marvin Gardens

I just installed an Armstrong 95% and they state that you can vent in different places. They say that the intake can be inside and the exhaust outside.

Now that is a pressure difference. Not a big one but there is a difference in pressure especially when the wind is blowing.

I was going to do an inside intake but the energytrust.org says to get their rebate of $200 I have to have the intake outside.

The one I vented up a chimney and did the intake out the back is working fine.

Where the pressure switch comes into play is if the pressure in the exhaust gets too high, then it will shut down. This assumes that the vent is blocked. In fact to test them I just put my hand over the exhaust and it shuts down.

They are rated for indoor air, yes. But not for going into diff press zones.

The press differential is measured by the double tap press switch and will cut out if not with in a specific range of WC".
I had a go round with my OLD,old school dist. He told everybody they could run pipes to diff side of home.
I called Allied air tech service and they said "NO WAY JOSE'" direct quote, that. So they gotta go out on the same side.

Don't take my word for it, call Armstrong .

Prince1 · 10-21-2008, 09:12 PM

I appreciate all the info....keep it coming if anyone has more thoughts. I had a contractor give an estimate and he thought it would be fine if they were to do the install. Thanks again.

Prince1 · 10-21-2008, 09:13 PM

MAybe I can run them both out the back, but I am getting near a dv gas fireplace. Ugh.

tk03 · 10-21-2008, 09:30 PM

READ....That will tell you. The I&O will address the venting issues. They tell you what you can do not what you can't do. I they don't show it in pictures and do not talk about it in text best bet is do it.
Two different walls is going to be a problem if they use a suction/pressure switch as opposed to a pressure switch. Two different walls and a suction/pressure switch will give you shut downs.
You stated the vent and air intake need to be no more then 24" apart. How much easier is it to understand. Not to sound coy but it does not matter if we undersatnd it or not, it is what they decided to pay for in the certification process.

**beenthere** · 10-21-2008, 11:20 PM

For every install that works fine with the intake and vent on opposite sides of teh house. There are 100 that don't.

hvaclover · 10-21-2008, 11:36 PM

Quote:

Originally Posted by beenthere

For every install that works fine with the intake and vent on opposite sides of teh house. There are 100 that don't.

C'Mon! Give more detail. You're sand baggin' us.

**beenthere** · 10-21-2008, 11:43 PM

LOL...

If I can't get both to the same wall. I use indoor air for combustion. It works better.

I hate cutting PVC at 1 in the morning to get the heat going again.

hvaclover · 10-21-2008, 11:48 PM

Quote:

Originally Posted by beenthere

LOL...

If I can't get both to the same wall. I use indoor air for combustion. It works better.

I hate cutting PVC at 1 in the morning to get the heat going again.

If it's 1 in the morning no sane customer would have me in house, heat or not...I get cranky after 12am.

hvaclover · 10-21-2008, 11:51 PM

Quote:

Originally Posted by hvaclover

If it's 1 in the morning no sane customer would have me in house, heat or not...I get cranky after 12am.

By the way...how come none us "Pros" brought up a concentric termination? That only needs a half brick.