Water Heater / Furnace Odor

Old 01-08-01, 11:25 AM
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I have a gas furnace that utilizes a forced-vent exhaust. I did have an electric water heater that failed last Summer. I put in a forced-vent gas water heater because there was no place for a natural vent chimney. It worked great and we saw the savings on our utility bill immediately.

When Winter arrived several months later, there were certain times of the day when we would get an odor in the house. It was somewhat like rotten eggs, but also a like a sewer drain smell. Whenever we smelled it, I would go down to the utility room and find the water heater running, and venting. It SEEMED like the smell would occur if the water heater was running just after the furnace shut off. I suspected that the vent on the water heater was drawing some of the recently burned products out of the furnace vent pipe and into the utility room. Burned natural gas odorant has the characteristic smell of rotten eggs. There are leaks in the intake ducting in the utility room which would have a slight negative pressure inside and thus suck up gases in the room and spread them through the house. As a side note, the smell in the house seemed to be concentrated in only a few rooms. We could put our noses to the furnace outlets and smell the odor. We could also smell it in the utility room.

My first attempt at a fix was to install an outide vent source to the utility room. The vent pipe simply terminated over the water heater withing a foot of it's power vent intake. Still, the problem continues.

What is so frustrating is that we cannot locate a definite source of the smell, if we could, I'm sure we could solve it. Due to the sewer smell we suspect, I made sure that the floor drain in the utility room had water in its trap. Sometimes the traps in unused drains dry up and vent sewer gas.

I also considered wiring a relay to the furnace vent fan such that it would run s=whenever the furnace called for it or if the water heater vent is running in order to make sure that fumes weren't being drawn back in. Remember that it doesn't happen all of the time, only once in a while, and only in certain parts of the house.

I know asking you to determine the cause of this problem is like asking you to look in a crystal ball, but have you seen (or smelled) any problem like this before. Where would you suggest I look?

Thank you.

Mark Peterson
Old 01-16-01, 11:12 AM
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More info on the situation.

Whenever we have noticed the odor, I run downstairs to learn what I can. I have always found either the furnace running or just the furnace blower, which we often run alone. Somtimes the furnace will be burning away, or just have shut down. Other times the water heater may be running, or just just down as noticed by a warm outlet, someitmes it was cold. Bottom line - I[ve never found a pattern. However, the furnace running may simply be incidental. I'll explain.

I was sitting in a chair in our upstairs living room when I noticed a little bit of the nasty smell. I was sitting right over a register. I put my nose down to it and sure enough, the smell was there. I ran downstairs to find a cold furnace and water heater outlet, neither was running nor had been recently. However, the smell was lingering in the utility room. I think that at has been most apparent when the furnace blower is running since it does a better job of dispersing the odor into the house.

I was sniffing up, down, here, there, everywhere trying to find a source. It seems to be strongest at the floor and around the furnace. The floor drain trap is wet. The interior of the furnace fan compartment and adjacent intake duct is clean. The A/C evaporator coil and duct is clean. The PVC soil stack does enter the floor right behind the furnace but it's clean out plug is tight. I cannot figure what in the world is causing this?

Any ides now based on my new findings?


Old 01-16-01, 02:06 PM
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I must be in this business much too long. Thanks for your second and more detailed update. However, I have heard all this hundreds of times. Not meant to be brash mind ya.

The point is you never mentioned a word about taking any of my suggestions or advice to contact the gas utility and requesting the services I recommended.

I sure hope you take some action to further investigate where that odor is and locate it's source. It's possible the odor could be a hazard to which you a being warned of but not yet responed to.

For the benefit of yourself and any others in the house, may I once again suggest you take some action, put aside the time needed and contact the pros and not rely on your nose.

Good Luck,
Old 01-16-01, 04:55 PM
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Hi Mark,

Gettin' pretty stinky in there? *G*

We had that feelin' a couple of weeks ago...

I agree with Tom about checking the gas end of the equation first...hope you've done that..

A couple of questions if your computer and house still exist...

Could you draw me a visual picture (or take one and post the URL) of your heater and furnace exhaust vents and also (if applicable) the combustion air intake vents?...I'm curious about proximity and location...measurements are nice if possible. Also, site them as they relate to the prevailing winds in your area as well as to any drifting snow you may have.

Also, could you describe the location (proximate to the heater/furnace vents)and size of the fresh air inlets for your utility room...?

Did you ever run the furnace before this years heating season started but after the water heater was installed? Did you notice anything out of the ordinary with your furnace last year (before installing the water heater)?

Are you on natural gas or LP?

Have you changed the filters recently in your heating plant?

Do you have any other venting appliances like a vent hood over a stove or a powered bathroom vent...?

If you have eliminated gas leaks (raw gas that is) from the equation, you still have a potentially unsafe situation due to carbon monoxide. Usually the same problems which cause vent spillage or reverse vent flow cause incomplete fuel combustion which release much higher concentrations of CO and into spaces where it could really give you and your loved ones a bad day...

After my problem (and because I was installing a high performance vent hood over a cooktop), I purchased a CO detector and use it to test for inadequate venting and/or combustion...as well as to warn us if something goes wrong..CO is a silent killer. I heartily recommend it...

Hope you'll get back to us with what you've found and that you and your family are safe...

Good luck!


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