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Old 08-04-2009, 03:31 PM   #1
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Furnace fan / bathroom fan - connected?


Hi,

We moved into our house this past winter and quickly discovered that when the furnace starts up, the fan in the master bath starts at the same time. And when we turn on the bath fan, the blower for the furnace starts as well. Is this normal? The house was built in 1968, but was recently remodeled. Now, we have a strange smell coming out of the vents for some reason. I think it smells like rotten hay, but my wife says it smells like fresh poop. Looking for a possible source, I discovered an outside fresh air vent that is drawing air into the house when the AC is running (aka, the furnace fan). Is that normal? Is it some sort of air exchange system? I don't see the classic air exchanger anywhere. All the vents lead to the furnace. I'm at a loss as to where the smell is coming from and why we're sharing our treated air with the outside!

We live in Minnesota and I'd just as soon keep the wet, hot air outside in the summer and cold, dry air outside in the winter.

Dan

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Old 08-04-2009, 08:16 PM   #2
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Furnace fan / bathroom fan - connected?


It sounds like a home made air exchange system, Fresh air to the furnace and exaust at the same time. Sounds a little goofy to me but I have seen stranger things. Does the smell happen only when the fans operate (pulling is oders from outdoors or when the system is off also. My brother bought a home and found a constant sewer smell and found the horizontal overhead sewer runs had rotted on the top of the pipes and the previous home owner could not figure out were the smell was coming from so they had masked the oder by doing other creative things. Possably this was done for a simmilar reason.

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Old 08-05-2009, 09:37 AM   #3
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Furnace fan / bathroom fan - connected?


The smell just started when we were gone for a few days. When I walked in to the house, I was sure one of the kids forgot to flush the toilet. After checking those, I realized it was coming from the vent. I only smell it when the fan is running, so maybe it's coming from outside. It doesn't really smell outside, so I'm not sure.

If that is some sort of air exchange system, it's got to be pretty inefficient. I'd like to find the person who installed it (just to ask questions), but there is no tag or sticker on the furnace. There is no manufacturer tag either. I've never seen a furnace like this one either. It's in the middle of my lowest level and doesn't have a regular chimney. Instead, it's hooked to a power vent for exhaust. There's another pipe running next to the exhaust pipe for air intake. There is some sort of PVC setup on the side of the furnace that has water in it (I can hear the water bubble). It's not a humidifier (it's not hooked to the ductwork), so I have no idea what that is. There's a zone control on the fresh air intake, but that seems to always open when the fan starts.

Thanks for the reply. My search for the smell (and understanding why they did this) continues...

Dan
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Old 08-05-2009, 09:46 AM   #4
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Furnace fan / bathroom fan - connected?


It sounds like your furnace is a high effeciency model. They burn more efficiently so they don't need a chimney but can discharge their exhaust gases out the side of the house. The small PVC pipe you see is to take water to the drain. I don't know for sure, but I think Natural Gas has water vapour in it. The high efficiency furnaces burn more completely leaving more water condensation that needs to be removed from the furnace.
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Old 08-05-2009, 10:02 AM   #5
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Furnace fan / bathroom fan - connected?


I guess high efficiency is good, right? That reminds me, there is no screen on the exhaust vent. It's only a matter of time until something crawls in there. Always something to work on...

I think you're right about the water, there is a tube running to my floor drain.

Thanks for the reply.

Dan

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Old 08-05-2009, 10:37 AM   #6
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Furnace fan / bathroom fan - connected?


You don't want to put a screen on the exaust or intake. They will freeze in the winter and you will loose heat.
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Old 08-05-2009, 10:47 AM   #7
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Furnace fan / bathroom fan - connected?


Ah, so it was intentional on the installer's part. I was wondering about that. Glad I mentioned it! Right now, the pipe comes out of the wall about 8 inches above my patio. There is an elbow (not glued) making it horizontal to the ground. Can I add an elbow to turn it straight up and then two more to point it towards the ground? Or would that trap moisture in the pipe? What's keeping rodents from crawling in there?

In any case, thanks for the reply. You saved me from an expensive mistake...

Dan
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Old 08-05-2009, 10:56 AM   #8
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Furnace fan / bathroom fan - connected?


No, you can not add more elbows as the termination must be done per manufactures instructions. More elbows could cause problems also.
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Old 08-05-2009, 05:33 PM   #9
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Furnace fan / bathroom fan - connected?


Hopfully the fresh air intake to the furnace duct work is not to close to the furnace exaust. We do not want to suck in the furnace or water heater fumes.
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Old 08-06-2009, 12:24 AM   #10
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Furnace fan / bathroom fan - connected?


Quote:
Originally Posted by drtbk4ever View Post
It sounds like your furnace is a high effeciency model. They burn more efficiently so they don't need a chimney but can discharge their exhaust gases out the side of the house. The small PVC pipe you see is to take water to the drain. I don't know for sure, but I think Natural Gas has water vapour in it. The high efficiency furnaces burn more completely leaving more water condensation that needs to be removed from the furnace.
yes , flue gas generally has about 70+ % water vapor
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Old 08-13-2009, 08:06 AM   #11
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Furnace fan / bathroom fan - connected?


Not sure if this is related to my previous post, but it could be. I went up on my roof last night and discovered my sewer vents are plugged. That's plugged as in capped. Something on the cap said something like "knock out plug". Shouldn't these vents be open? Why would they be plugged? Maybe for leak testing or something? I'm guessing they should be opened up. Any tips for getting the plug out so it doesn't fall down the vent? Could this explain the musty smell we've been having?

Dan

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