fresh air???

[Thezapper]

hello everyone just wanted to put something out there, my buddy just had his furnace replaced its a keep rite high efficiency furnace, install looks great except for the fresh air intake is sucking the basement air, its not routed outside. he told me that the installer said its better like this, because it would cause less condensation in the air? I agreed and changed subjects, I didn't want to cause a ******* match as im not a hvac tech nor I pretend to be one.
his home is a 1960s bungalow, not well insulated.

so my question is ....is this rite? is there any fact to this?

 

[George-V]

Not a hvac tech but it doesn't sound safe to me.

 

[GDPossehl]

I'm no HVAC specialist either, but I would imagine that the temperatures from the crawl space would be much warmer than the outside air during winter making the furnace more efficient, but as far as condensation goes I'm not sure. I would think the winter air would be less humid than the basement air.

 

[ripperd]

In a tight house some outside air is important for both air quality, and combustion (if the furnace doesn't have a separate combustion air intake).

In an old drafty house you can probably get away without it. But still not a good idea I don't think.

But I am far from an expert.

 

[ripperd]

Wait, is this combustion air intake, or just a fresh air intake?

 

[Thezapper]

its the combustion air intake,

 

[brewchief]

Some furnaces are rated to use either inside air or have an intake pipe, as long as it is allowed by the manufactur then it is OK. Most times I prefer a separate intake but in some cases you can simply look at where the vents need to come out at and see a huge potential for a intake that will get blocked with snow.
I wouldn't worry about it.

Sent from my XT1254 using Tapatalk

 

[Brian_WK]

FYI the colder the air is going into the furnace for combustion air, the denser it is, the more efficient the furnace is. It can be up to 2%. I always ran the 2 pipes unless physically impossible.
Sounds like the installer was being lazy and gave a BS excuse about it being better. If you are pulling combustion air from inside you are just causing your house to be in a negative pressure which allows air infiltration in every crack.

Brian

 

[Thezapper]

FYI the colder the air is going into the furnace for combustion air, the denser it is, the more efficient the furnace is. It can be up to 2%.Brian

could you explain this? if the air is colder wont it have to burn more fuel too?

 

[rlitman]

FYI the colder the air is going into the furnace for combustion air, the denser it is, the more efficient the furnace is. It can be up to 2%.

That's got to depend on the furnace.
Colder air will certainly increase the maximum heat output, but if the air/fuel ratio remains correct, it should not affect efficiency.

 

[bonneyman]

If it's the combustion air, you're messing with possibly killing someone. The furnace is burning gas, and it needs oxygen to do that. That's why why provide fresh air vents or combustion air ducts to allow the furnace to draw in air from outside to burn.

You don't want it sucking the air from inside the living space. Then it's #1 competing with the people #2 if the house is sealed tight enough it will create a low pressure condition inside the home #3 in bad cases the flames will come out of the furnace looking for air to burn. This could cause a fire.

As has been said in older, "leaky" homes enough air penetrated to save them. In today's modern efficiency-oriented air-tight construction you're just playing with fire. Literally.

 

[GDPossehl]

FYI the colder the air is going into the furnace for combustion air, the denser it is, the more efficient the furnace is. It can be up to 2%. I always ran the 2 pipes unless physically impossible.
Sounds like the installer was being lazy and gave a BS excuse about it being better. If you are pulling combustion air from inside you are just causing your house to be in a negative pressure which allows air infiltration in every crack.

Brian

If it's the combustion air, you're messing with possibly killing someone. The furnace is burning gas, and it needs oxygen to do that. That's why why provide fresh air vents or combustion air ducts to allow the furnace to draw in air from outside to burn.

You don't want it sucking the air from inside the living space. Then it's #1 competing with the people #2 if the house is sealed tight enough it will create a low pressure condition inside the home #3 in bad cases the flames will come out of the furnace looking for air to burn. This could cause a fire.

As has been said in older, "leaky" homes enough air penetrated to save them. In today's modern efficiency-oriented air-tight construction you're just playing with fire. Literally.

These two are definitely the most helpful answers. I was under the impression previously that it was a fresh air intake for the circulating air rather than combustion. The fresh, cold air for combustion is definitely better and a 2% efficiency improvement estimate is probably fair.

 

[zmaxmotorsports]

The biggest advantage of the piped in combustion air is that youre not wasting air you already heated to support combustion in the furnace.

 

[bonneyman]

The biggest advantage of the piped in combustion air is that youre not wasting air you already heated to support combustion in the furnace.

That, too!

 

[Thezapper]

Thanks guys I'll let my friend know and I'll let him figure it out.

 

[Milton Shaw]

As that is a gas burning device I would suggest getting a CO2 Detector and put it close to the unit in case there are any problems. Same with Gas water heater. Just extra protection for the family for approx $50.

 

[sselander]

I have a gas boiler with the "fan in a can" that works well
Both my intake and exhaust go through the foundation wall direc to the outside, and are well separated.

http://www.fieldcontrols.com/cas-3-oil-and-cas-4-gas?page_id=94

 

[Jackfre]

You are in Canada, but I believe the U.S. Code, NFPA54 and the Canadian code are close to the same. Please check this out. 54 says that you need 1sq in of open space per 1000btu of input. A 6" round is 28 sq in so it can supply 28000 btu. How big is the furnace? Also there should be two pipes. One high, one low. The problem is that when it gets really cold out and someone walks into the basement and that cold air is spilling into the space they block of the intake. Happens all the time. In fact, if you look at the gooseneck at the bottom of the intake pipe you will solve one of life's great mysteries. It will be filled with all the mismatched socks you have been looking for.
The post about the fan in a can is best here. I much prefer the Tjernlund Combustion air Enforcer to the FIAC, but both do essentially the same thing. They interlock with the burner and only provide outside air when there is a call for heat. The problem with using either of these is that you will have to deal with the socks.

 

[LS6 Tommy]

IDK about Canada, but in the US, the furnace cannot take combustion air from the same space as return air...

Tommy

 

[larry4406]

Water heaters take air from the room they are in to provide combustion air to the appliance.

Many furnace applications do the same, including high efficiency models. A quick google search of Lennox products shows this method. There are certain criteria to be met to enable this method. As always, check the installation manual of the equipment and read the criteria carefully.

 

[Thezapper]

Water heaters take air from the room they are in to provide combustion air to the appliance.

Many furnace applications do the same, including high efficiency models. A quick google search of Lennox products shows this method. There are certain criteria to be met to enable this method. As always, check the installation manual of the equipment and read the criteria carefully.

thanks larry the picture above is exactly what im talking about, is there any advantages of plumbing the intake this way? because im not buying that it is deadly as someone posted, but if im wrong could you explain why?

 

[Jackfre]

The other part of 54 deals with "confined & unconfined" space. You are required to provide 50 cu ft of unconfined space/1000btu of input. I have seen so many places that figure their requirements when the builder finishes the space and it is empty. When I've gotten there, you find a pile of stuff 4' tall taking about 40-50% of the space. Also, once the place is finales, while the heating guy is on his way out the door, the homeowner is dragging a pile of 2x4's down the bulkhead to enclose the unsightly equipment. Happens all the time.
The thing is, that in the north you close your doors in October and don't open them again until April. The CA issue becomes stressful to the equipment in the middle of the night when it is running and no one has come in or out tf the space. You create a negative pressure in the house. Heat may go off, but even if it doesn't it is really stressful to the equipment and therefore the owners dollars. So, assuming a no heat call and you get a tech out first thing in the morning. As soon as you open a door the problem is solved.

If you think there is no CO produced by incomplete combustion, spend a night in that space and let me know how you feel in the morning.
Milton's suggestion of a CO detector is the best advice in this post.

 

[HoosierBuddy]

I'm one of those guys that HVAC guys love to hate.

I installed my own furnace.

Step 1 was reading the directions. They specifically indicated I could EITHER use combustion air from the home OR install a PVC run to pull it from outside. Both cases included specific dimensions, distances, lengths, etc.

After considering it all, I ran a seperate PVC run for combustion air to the outside as:

1. It wasn't impossible.
2. If you pull combustion air from the heated space, that air has to be "made up" from somewhere. It seems to me that it will be made up when the negative pressure created by the combustion blower is balanced by air infiltration through cracks or gaps in the building envelope...meaning unconditioned air will be drawn into the home. That did not seem optimal.

Just a layman's view. But...there's no getting around the fact the installation instructions specifically said it was OK to install it either way. I'd suggest the OP's friend look through the manual that came with his furnace. If the HVAC guy didn't give it to him, 99% chance it's online in pdf form.

Phil

 

[Brian_WK]

I'm one of those guys that HVAC guys love to hate.

I installed my own furnace.

Step 1 was reading the directions. They specifically indicated I could EITHER use combustion air from the home OR install a PVC run to pull it from outside. Both cases included specific dimensions, distances, lengths, etc.

After considering it all, I ran a seperate PVC run for combustion air to the outside as:

1. It wasn't impossible.
2. If you pull combustion air from the heated space, that air has to be "made up" from somewhere. It seems to me that it will be made up when the negative pressure created by the combustion blower is balanced by air infiltration through cracks or gaps in the building envelope...meaning unconditioned air will be drawn into the home. That did not seem optimal.
This is a good reason!

Just a layman's view. But...there's no getting around the fact the installation instructions specifically said it was OK to install it either way. I'd suggest the OP's friend look through the manual that came with his furnace. If the HVAC guy didn't give it to him, 99% chance it's online in pdf form.

Phil

What I was taught when doing combustion efficiency (another thing I did on every furnace start up that many don't). Is for every 40F Degrees difference lower combustion air temp the efficiency goes up 1%. My real word testing shows it is closer to 60F Degrees is about 1%. And a 1% increase in efficiency is a 1% decrease in fuel costs.

Brian

 

[Slowgsr]

I would prefer it inside. Mines been blocked by snow before, it ***** since depending on when it happened youll come home to a cold house, or wake up to one

 

[zmaxmotorsports]

I'm one of those guys that HVAC guys love to hate.

I installed my own furnace.

Step 1 was reading the directions. They specifically indicated I could EITHER use combustion air from the home OR install a PVC run to pull it from outside. Both cases included specific dimensions, distances, lengths, etc.

After considering it all, I ran a seperate PVC run for combustion air to the outside as:

1. It wasn't impossible.
2. If you pull combustion air from the heated space, that air has to be "made up" from somewhere. It seems to me that it will be made up when the negative pressure created by the combustion blower is balanced by air infiltration through cracks or gaps in the building envelope...meaning unconditioned air will be drawn into the home. That did not seem optimal.

Just a layman's view. But...there's no getting around the fact the installation instructions specifically said it was OK to install it either way. I'd suggest the OP's friend look through the manual that came with his furnace. If the HVAC guy didn't give it to him, 99% chance it's online in pdf form.

Phil

No hating here.

 

[zmaxmotorsports]

I would prefer it inside. Mines been blocked by snow before, it ***** since depending on when it happened youll come home to a cold house, or wake up to one

You need to figure snow/wind conditions when you install the equipment,Ive been called out to more than one over the years where somebody ran the pipes straight out of the house facing to the north 12" off the ground.