Does gas furnace need fresh air?

Franky123 · 10-14-2009, 03:28 PM

Hi,

We moved last year and the home has a 5 yr old gas furnace. Due to major renos when we moved I had the ducts cleaned. The cleaner noted that one of my air intakes was going straight outdoors, thus sucking fresh cold air (in winter) to supply the furnace with fresh air. He suggested I replace it with a passive intake : by means of an insulated tube coming from the outside and placing the other end next to the furnace.

I have 4 interior intakes. The flow was found to be sufficient with the 4 (it was measured by a pro).

I’m wondering if I just cancel the exterior intake alltogether and add an interior one for a total of 5 - would this be sufficient or does the furnace need a passive intake for fresh air as suggested by the cleaner?

dac122 · 10-14-2009, 04:01 PM

Not sure you're speaking the right language here. Some high efficiency furnaces call for outdoor air for combustion usually with PVC. I have no idea what is mean by it being passive, or that you have 4 interior intakes.

Are we talking about ductwork returns perhaps? Pics might be in order for you to better explain this.

No offense to whoever cleaned your ductwork but a qualified HVAC pro is who you need to provide reliable information on how to handle your furnaces combustion air, if thats what we're talking about.

**beenthere** · 10-14-2009, 06:46 PM

Your Home may or may not need that fresh air intake.

Can't tell from here.

There should be at least a manual damper to control how much air it brings in. If not, have one installed. Or, better yet. Get the Aprilaire fresh air vent control that will allow it to be controlled automatically.

Red Squirrel · 10-14-2009, 07:00 PM

There is an exhaust for the CO produced by the furnace. The air that is exhausted out needs to be replaced or it would try to create a vacuum and I doubt the motor could, so the CO would have trouble escaping. So yes you do need two pipes, one for intake and one for exhaust. Normally they are black PVC, the same used for drain plumbing. (I think... I'm not an expert).

**beenthere** · 10-14-2009, 07:08 PM

Some areas don't allow ABS, others do.

What the OP has, is not an intake for combustion.

simphead · 10-14-2009, 07:27 PM

Beenthere are you familiar with a problem where the draft motor does not turn on, therefore the pilot does not light? When heat is comanded from t stat, nothing happens. I am at my sisters. I have the same furnace. Mine works like this. Heat comanded. Draft motor starts. Ignitor lights. Thermocoupler sees flame turns ignitor off. Burner lights. fan turns on. I can get draft motor to run by disconnecting one of the in line sensors with red wire connecting all. So I know that it does work. What is my next step. John

Plumber101 · 10-14-2009, 07:38 PM

On the control board is there an LED flashing and if so count the number of flashes. There should be a code chart and post results

**beenthere** · 10-14-2009, 07:54 PM

Could be blown fuse.
Bad wire from stat.
Bad stat.
Bad control board.
Bad inducer motor.

Plumber101 · 10-14-2009, 07:55 PM

Yuri,

He started a new thread

hvac122 · 10-14-2009, 08:31 PM

The pipe that is bringing in air sounds like fresh air for the house. Here it is code to have it and it is tied into the return air duct. It is different than combustion air which sounds like the other vents you have. The idea is that with houses being built tighter these days there needs to be some means of letting the house breath so it does not go into a negitive pressure.

Here our code doesn't let us put any damper of any sort in the pipe. I do agree with beenthere that it would be nice to control it somehow.

I would call your local codes department before you do anything and see what they have to say.

How old is the house?

Franky123 · 10-14-2009, 09:27 PM

House if 45 yrs old.

By passive air I mean it is not motor aided or connected to the intake lines.

The pro who checked our air flow is a furnace tech, not the cleaner (2 separate inspections).

Passive air is an insulated 6" pipe which goes from exterior and the other end is placed near the furnace so that the flame can draw fresh air as needed.

I have been told this is code for our area so I think this is what we have to go with.

Thanks,
Frank

hvac122 · 10-14-2009, 10:08 PM

That would be the combustion air for the furnace and is needed.

Franky123 · 10-15-2009, 06:46 AM

Thanx hvac,

But should I just leave as aforementioned or does it have to be tied into a return vent? (sorry I kept saying intake - not correct term).

Thanx,
Frank

**beenthere** · 10-15-2009, 06:50 AM

Although some contractors will use that as a combustion intake.

It is not. Unless you have a supply vent in your furnace room.

It is a fresh air intake for your house, not a combustion intake for the furnace.