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Old 09-25-2012, 07:38 AM   #1
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Cat Pee Smell, Humidity, soil gas, radon & hardwood floors. - What a mess!


I seem to have dug quite a hole for myself and am looking for expert guidance. It started when we bought a 30 y.o. home last December (southern Illinois). We decided to renovate it by installing a hardwood floor (I did it myself), where there was once carpet, throughout the whole first floor of the house. You can read about it here: Crawlspace preparations for moisture control

When the floor was just about complete, and after reading some of the flooring threads, here at diychatroom.com, I decided the vented crawl space put us at risk to having the floor warp or cup. It seemed the best course of action was to follow the current state-of-the-art method to plug the foundation vents with cinderblock and then to fully encapsulate the crawl space. I think I did a fairly thorough job of this, but it isn't exactly "water tight".

To complete the crawl space encapsulation job, the current recommendation is to condition that air. The insulated HVAC duct-work runs through the crawl, so to accomplish this I made an opening in both the supply and return ducts, at opposite ends of the crawl. The supply opening is a standard 4" x 12" grill, and the return is slightly larger.

Now, there is a new odor in the house that smells like cat urine. If the house is closed up, it can get pretty strong. I consulted the very reputable and knowledgable supplier of the encapsulation materials and he said it sounds like soil gas. As I see it, even though the crawlspace is encapsulated, there is some of the soil smell passing through some of the leaks.

The supplier suggested that I get rid of the soil gas by installing an array of perforated 4" PVC drain pipe under the encapsulating membrane and use a radon fan to exhaust it. I will install that radon remidiation fan in the garage attic and vent it through the roof. It would look something like this: http://www.infiltec.com/tg3fg7.jpg and they call it "sub-membrane depressurization". Sounds logical, I guess, and I don't seem to be the first person doing it.

So now I am wondering, what is this going to do to my HVAC capacity? We have a 20 y.o. Carrier heat pump in fairly descent condition. The way it seems to me, the fan will be sucking air from under the membrane. That partial vacuum will cause the crawlspace air to make it's way through any imperfections in the liner. In turn, that crawlspace air will be made up by my conditioned air that's coming in via the opening in the supply line and through any leaks in the house itself.

It seems that this system is potentialy wasteful and my existing heat pump will be stressed.

For all you experienced HVAC folks, what do you think of this situation? Am I okay? Am I not? Why?

Thanks in advance for all your help.

Murph

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Old 09-29-2012, 02:29 PM   #2
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Cat Pee Smell, Humidity, soil gas, radon & hardwood floors. - What a mess!


I thought I'd report on the results of my soil gas remediation go-around. Look at the attached sketch of my crawl space

Following the expert advice, I purchased about 18 lengths of 4" x 10' perforated drain pipe. I slit the encapsulating membrane at the joints of the array and slid them under the vinyl. This was pretty easy. I didn't use any glue, just the mated the drain pipe. I did put an end cap on the end of each run. I figured it would be better to force the incoming air through the perforations, than have it rushing in on an open end of the pipe.

The joints to not need to be joined, just near each other. Somewhere in the middle of the array, I inserted a 4" Tee, to be used as the central pick-off to the fan. (You can see it sticking up in the photo, along with the solid pipe runners
). I was able to run the solid exhaust pipe through the joist at the end of the home and into the garage. From the garage, I ran the pipe vertically into the garage attic to where where the fan is mounted, then out the roof.

All-in all, it wasn't a terrible job, but I am very glad that it's over. I'm really tired of the crawlspace and I'm getting too old for this s**t.

I am pleased to report that within 12 hours of turning the fan on the smell was greatly reduced. Now, it's 24 hours later and the smell is G-O-N-E! Terrific!

Now, I have no idea what effect this will have on our utility bills, from having the air sucked out. The fan itself only draws about 1/2 amp, so that is no biggie.

So, those of you who are considering encapsulating their crawlspace, may want to plan ahead about the soil gas remediation. One beneficial side effect, if there is radon present, this array will remove it too.

Cheers.

Murph
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Cat Pee Smell, Humidity, soil gas, radon & hardwood floors. - What a mess!-image00007.jpg   Cat Pee Smell, Humidity, soil gas, radon & hardwood floors. - What a mess!-tg3fg7.jpg   Cat Pee Smell, Humidity, soil gas, radon & hardwood floors. - What a mess!-shows-tee.jpg  


Last edited by MurphyMan; 09-29-2012 at 03:53 PM.
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Old 09-30-2012, 05:07 AM   #3
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Cat Pee Smell, Humidity, soil gas, radon & hardwood floors. - What a mess!


Glad it worked out for you.

Did you check your RH in the crawlspace when you had the odor? Cooling crawl to quick can raise its RH and cause odors.You said the return in the crawl is larger then the supply. It shouldn't be larger, since that causes the crawl to depressurize, and draw in odors to the house.
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Old 09-30-2012, 08:51 AM   #4
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Cat Pee Smell, Humidity, soil gas, radon & hardwood floors. - What a mess!


Thanks for the reply.

I have been monitoring and recording the crawl temp & RH for the past month. It has been relatively steady with a temp of about 70 F and a RH of about 63. We have had the new fan only running for two days, but so far it hasn't seemed to affect the RH.

As far as the HVAC openings in the crawl ductwork. Like I said, the supply is a 5'x12'. The return grill is probably 8" x 12. Not too much larger.
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Old 09-30-2012, 09:09 AM   #5
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Cat Pee Smell, Humidity, soil gas, radon & hardwood floors. - What a mess!


Your return is too big, its putting your crawl into a negative pressure. You really don't need the crawl to be the same as human comfort temp.

Your humidity is too high also.
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