Cold combustion air intake making basement cold

[101mph]

Hi Guys,

I've got a new house with a high efficiency furnace. The basement is insulated well and the house is very tight. As you can see from the pictures the cold air intake for the furnace combustion comes in and the pipe is open near the floor.

It's basically spilling out cold air into the basement constantly which is making the basement pretty cold. So I was looking for suggestions on how to stop this from happening.

I've been doing some research and some suggest to try putting a "J" pipe connecting to the cold air intake pipe to keep the cold air from spilling out all the time.

Other suggestions are to use a mechanical damper that is activated to open when the furnace turns on.

And other suggestions are to close off that entire area of the furnace and water heater so that the cold air stays in there.

The last 2 are a little expensive and the first one doesn't sound like it'll work (I've already tried a 5 gallon bucket under the pipe and it didn't do anything - cold air still spills over the edge of the bucket).

Suggestions?

 

[jeffer949]

I am no HVAC expert but I know on my High efficiency furnace that the intake and exhaust for the furnace is the 2 PVC pipes going into the actual furnace. I Do not see what the regular ducting is for. But I am curious to learn if there is a viable reason.

 

[finn]

My shop and house have high efficiency boilers with pvc intake and exhaust pipes, both diducted to the exterior of the house.

I have another house with a forced air 90% + efficiency furnace with a pvc exhaust, but the hvac guy ( same guy) used inside air for the inlet.

He says that the forced air furnace has three pressure sensors in the system, and when it is extremely cold, with blowing snow, the sensors go out of range and the system shuts down.

I know it happens at least once a year, even with the inside inlet, as water in the exhaust freezes on the outlet elbow and upsets the pressure switches.

Taking the bird screen seemed to help this condition from occurring.

The boiler only has one pressure switch, he says.

 

[Showkey]

Some areas or regions demand make up air..........but It’s just crazy you have a new home that is very tight and then you have a fresh air duct, which like having the window open 24/7. Sorta looks like the builder went cheap on meeting the fresh standard in your Home by skipping the recovery unit.

You should ask the installer HVAC guy if there a code restriction or requirements.

My tight house has a heat recovery unit on fresh air inlet. There are dozens of brands of these recovery units. I have a choice when to run the unit either by humidity, timer or random or not at all.

a versatile compact Heat Recovery Ventilator (HRV) with top ports. With this machine you be able to reclaim energy from exhausted stale indoor air to temper incoming fresh air. Heat is retained during cooler seasons, and removed during warmer seasons. These systems capture about 70 percent of the energy already expended to temper incoming air.

 

[Viper98912]

Are you my neighbor? lol.

I also have a brand new home here in SE Michigan, and have the same exact setup. Identical really; same HVAC unit, pvc piping, setup, and open duct coming from the outside. Must be a Michigan thing.

I find that the long pipe outside + 90 degree turn + 6-7 ft vertical drop is long enough to keep the outside air outside. If I stick my hand inside the duct, you can feel the cold air, but I don't feel anything actually flowing in or out of the duct. My basement is a little colder than the main floors (as expected), but it's definitely not immensely cold as the outside, and the basement vents are also closed as well.

 

[AA7483]

The air is definitely not for the furnace. The furnace gets its combustion air from the pvc pipe adjacent the to vent pipe. Its totally sealed combustion. The air is either for a hot water heater or as someone else mentioned if the house is really tight it could be a crappy make up air setup.

 

[casetractorfarmer]

Shouldent the air intake be sucking air from the outside and not the basement

 

[AA7483]

It is for the furnace. Assuming the pvc pipe on the left is piped all the way outdoors.

 

[ItsNemo]

Am I seeing this right, there's a 90 degree elbow on one of the PVC pipes that is just open to the air in the basement? And then the 4" metal duct is supposed to be making up the air that's drawing in?

This is definitely not how you install a high efficiency furnace.

PVC pipes should both bring air in and combustion exhaust out for the furnace itself. The other pipe is useless but could be used to put in an HRV, although might not be required by code in your area if you have exhaust fans.

 

[Radix2]

I'm in Michigan too, and just had a new furnace install - the outside air intake is not connected like yours- it is connected into the air return duct - so when the furnace runs it pulls some air from outside so no cold air coming directly into any room.

This intake is not for combustion, that is the second pipe to the furnace itself in your picture.

 

[AA7483]

Your absolutely right. I see it now. Piping the intake like that is fine provided there is enough available air in the basement. Apparently there was not in this case. I always run 2 pipes but its acceptable. In your case, If this is the only piece of equipment in the room, then pipe out the intake for the furnace and eliminate it. This is assuming there are other means for make up air due to the tightness of the house and the water heater has its own means for combustion air.

 

[CKS1955]

I'm in Michigan too, and just had a new furnace install - the outside air intake is not connected like yours- it is connected into the air return duct - so when the furnace runs it pulls some air from outside so no cold air coming directly into any room.

This intake is not for combustion, that is the second pipe to the furnace itself in your picture.

Are you my neighbor? lol.

I also have a brand new home here in SE Michigan, and have the same exact setup. Identical really; same HVAC unit, pvc piping, setup, and open duct coming from the outside. Must be a Michigan thing.

I find that the long pipe outside + 90 degree turn + 6-7 ft vertical drop is long enough to keep the outside air outside. If I stick my hand inside the duct, you can feel the cold air, but I don't feel anything actually flowing in or out of the duct. My basement is a little colder than the main floors (as expected), but it's definitely not immensely cold as the outside, and the basement vents are also closed as well.

I am also in Michigan. When we built our house we had duct from outside bringing air to the furnace room, but as with your setup both the forced air furnace and water heater have fresh air intakes for the sealed combustion. We also have a fresh air intake the for the return duct.

After we received our occupancy certificate we removed the duct just dumping cold air into the furnace room. That was 14 years ago. I believe the building code is designed for older 80% efficient units using interior air for combustion.

Jay

 

[6768rogues]

Some furnaces can be piped with one or two pipes. I would do some research and look inside the furnace to see if the combustion air pipe can be directly connected.

 

[101mph]

I guess that duct could be for the makeup air. I'm just concerned with the cold air coming from the outside.

I'm not sure why they have the intake air PVC pipe coming from the basement. In our last house all of these PVC pipes came from the outside as you guys have mentioned. I will take a look on the outside of the house but I'm almost certain there are no PVC pipes going to the furnace from the outside (it's a Bryant furnace BTW).

If there is something wrong with this setup, then how on earth could this have passed all the inspections and the "blow test" they did before we moved in? Maybe there isn't anything wrong, but probably not done the best way that it could've been. Builders are notorious for cutting corners when they can.

 

[AA7483]

Building codes a a minumum requirement. Just bc I passed inspection doesn't mean the best practices we're used. You should also take note where the vent pipe is located. In most areas the minimum distance from a window goes from 1 foot to 4 feet when you don't pipe the intake outdoors.

 

[Viper98912]

Just for clarification on my setup, the furnace has two pipes directly going outside (in and out) and then one pipe directly outside for the water heater. I don't have anything pulling air in from the basement.

 

[101mph]

Yea it's weird that the combustion air intake is coming from the PVC in the basement. Seems half assed but this is what I got in this place. I'm going to have the builder come over to see if he has any solutions to this cold air problem before I start into it. Although I have a feeling that he will say "it's normal".

 

[rlitman]

Can you post up some pictures of your furnace? Something isn't adding up here.

 

[AA7483]

Taking combustion air from the basement is fine provided there is enough air. Is it somewhat half assed? Yes. But there technically nothing wrong with it. If that large air pipe is strictly for air for the furnace eliminate it and pipe the furnace properly. If it's for the water heater too you'll need to make other arrangements to bring air in if the house is that tight. And finally if it's a new house make the builder make it right. It shouldn't be your problem.Why did the pictures get taken down?

 

[101mph]

I have to believe there is plenty of air. I think the water heater goes outside for the air, but I'll have to check.

The pictures were locked by Photobucket for some reason. That site is horrible so I just switched to a new file sharing site. Might have to reload this page to get them to show up. They are in this thread.

 

[rlitman]

Ok, I was able to download one picture. I see you posted three of the same image.
The top of the furnace has two PVC pipes. One is the combustion exhaust, and goes outside the picture. The other is the fresh air inlet, and is open to the room.

So your furnace has sealed combustion, and the installer didn't bother to pipe it outside. Yeah, that is totally half assed. And this is new construction?

So, now we need to know more about your water heater to know if you need some fresh air for that (though the needs would be far less than a 6" pipe in any case).

As for the furnace, you already have a fresh air pipe into the room. I think it could possibly be easier to connect the PVC that is currently open to the air into the side of that metal fresh air inlet, than to plumb it all the way outside. Then just cap the bottom of the metal.

 

[101mph]

That's a possible solution. I will look into that after what the builder tells me about this. I'll also look at the water heater setup (but I'm pretty sure it's all going outside).

I'm not sure why you're only seeing on image. There are 3 separate pictures. So maybe your browser just needs to be refreshed. This Photobucket **** is a pain...

 

[rlitman]

...I'm not sure why you're only seeing on image. There are 3 separate pictures. So maybe your browser just needs to be refreshed. This Photobucket **** is a pain...

I didn't see ANY images. I opened the page HTML source, copied the IMG links, and downloaded the three that I found. That was a HUGE pain in the ****, because it forced me to wait 15 seconds to click the download link on each, and then most of the time the timer reset and I had to try again before clicking that I am not a robot.

edit: tried with a different browser, and I was able to get three images now.

 

[101mph]

Is this any better?







Sorry I'm still getting used to this new file sharing site.

 

[eddieK]

I can't see pics.

But - If your furnace is a 90% or higher, there are two options for combustion air, (this is the air the burners require to provide SAFE combustion).

One is called free air, provided by excess space like a garage - The requirements are 1 sq.in. free area per 1,000 BTU’s from unit, but not less than 100 sq. in. One opening shall be within 12 “of the top and one within 12” of the bottom of the enclosure. The minimum dimension is 3”. sometimes 14 x 3 wall duct, sometimes 7" round pipe

The second way is direct where usually a 2" pvc pipe is solidly and continuously piped to the outside and is connected directly to the furnace. Both ways are manufacturers requirement and code compliant.

 

[rlitman]

Is this any better?...

Actually yes. But in the meantime, I've uploaded them to here.

 

[eddieK]

I use this -

https://postimages.org/

Just click on image and let it load (few seconds)
then the page asks what you want to load it to - choose hot link to forums.

Then paste it

 

[101mph]

Sorry about that. I guess I could've uploaded them like that also. Thanks for the help guys.

But yea I will try to get some pics of the hot water heater setup tonight.

 

[CKS1955]

I can’t believe they didn’t connect the combustion intake directly to outside air with PVC.

Jay

 

[Brian_WK]

Ya that is completely half assed. Im guessing the hot water heater, if it is GAS, needs make up air. So the builder though why run 2 pipes when I only need to run one since the basement air will be the makeup for both (l-a-z-y).
Putting a J on the pipe or a P (up then back down) will stop the air flow when nothing is calling for air. But the second you turn on a bathroom or kitchen exhaust fan. the Furnace or the water heater starts you will be bringing in cold air due to the house being a negative pressure.

Brian

 

[mygarageone]

Running the 2" combustion air to the outside , is not code required . However most do it .
But looking at the pic's he has makeup air piped directly youthe furnace ? I seriously doubt the house is that tight that he needs outside combustion air piped in separately ?
Did they do an air infiltration test ? There not state required but many counties require them now . But if the house is too tight , your required to put in a heat recovery unit .

It's very common for boca home's in fact there mandatory .

 

[sz0k30]

OK guys, maybe this discussion is only for high efficiency furnaces & water heaters. I've been in & lived in many houses with older gas/propane furnaces & water heaters and I've never heard of or seen any piping to bring air into the house. The only piping was a vent pipe that both units shared to let the exhaust out. So what's going on?

 

[101mph]

OK here are a couple pictures of the water heater. It's definitely exhausting outside.

A couple more of the furnace which is is rated at 96% efficiency. It is also exhasuting outside but the intake air is coming from the smaller pipe and using the basement air (I can't believe it's not coming from the outside ).

Sp the other duct workhas to be for the make up air. I don't know if you can see from the other pics ealier in the thread but there is also a second duct coming from the outside (for makeup air I presume) that is going directly into the cold air returns in the house duct work.

I know it's pulling outside air from this pipe because it is directly below our bathroom floor and that spot gets so cold it feels like you're standing on ice when the furnace is running.

The house must be pretty tight because the floor doesn't feel as cold in this area when the furnace is not running.

To answer the previous question - Yes they did a "blow test" on the house before we moved in and it passed. There is a sticker on the main breaker box stating as such. All the duct work seems are sealed and taped and the rim joist around the perimeter of the basement are sealed with caulk and insulated.

 

[BillK]

The only piping was a vent pipe that both units shared to let the exhaust out. So what's going on?

High efficiency furnaces bring in outside air for combustion and the exhaust is very cool. Mine has two PVC pipes that go to the outside of the house. One is the air intake and the other is the exhaust. That way when the furnace is burning it is not pulling cold air in through every crack and leaky window in the house.

 

[AA7483]

That is a typical power vented water heater. It uses combustion air from inside the home.

 

[mygarageone]

That is a typical power vented water heater. It uses combustion air from inside the home.

Yea but not enough to justify out side air being brought in , unless it's a code issue .

 

[ripperd]

FYI, I have a brand new house and I have the following:

1. 93% efficiency furnace. combustion air in and flue out are both PVC piped to outside the house.
2. waterheater is just like the OP's, takes in room air, power vented via PVC to the outdoors.

3. we have a outdoor air pipe into the utility room for make-up air, with the S curve described. very light flow in most of the time, a little more flow when we have bathroom/kitchen vent fans on.

4. we have an HRV (code in MN after 2015 I guess) for fresh air exchange. No pipe from outdoors into the cold air return like the old days.

This house is TIGHT. Rim joist area is spray foamed, everything is sealed really well.

 

[sixty4]

Sorry about that. I guess I could've uploaded them like that also. Thanks for the help guys.

But yea I will try to get some pics of the hot water heater setup tonight.

I have a question. How big is your hood over your stove. Almost looks like make up air that was never finished, if that duct goes outside.

 

[ItsNemo]

Yea but not enough to justify out side air being brought in , unless it's a code issue .

This. Hot water tanks like that never need make up air, just draw from the room and exhaust out the pipe.

Remove that big honking air leak of metal pipe. Pipe the PVC intake outside like it's supposed to be done. Call it a day. There's nothing more/less to it.

 

[matt_i]

Im in Mich and my house was built by a HVAC local contractor.

Its ~20yo now, and is not a condensing furnace, but I have the large intake fresh-air duct and have been trying to brainstorm solutions. I can think of how to actively control a damper with the furnace call-for-heat or the gas-valve energization but coming up blank on the hot water heater.

What I don't like is this house is not tight enough to keep the intake air from slowly infiltrating. I look up and see the double-wall hot-exhaust/vent pipe going up and it seems like its a leak up to the attic powered by the convection of the inner pipe. Any time the vent fan in the bath comes on it pulls in ambient air via the intake.

In homebuilding magazines everyone's doing blower door tests to see how tight they can build houses and this is like a 6" hole in the sidewall somewhere! I can understand the need for makeup air so the furnace isn't starved and/or has issues with "draft" by having to try to overcome the small gaps in a truly tight house.

The HRV sounds interesting but I'm still kicking around an automated solution...