Heating Duct Problem

[TromboneAl]

A month ago DW and I heard a chewing noise coming from our forced air heating vents (in the floor). The next day I set out traps and caught two mice. I think I got them all, because no mice have been caught in the traps since then.

Looking into the registers, I saw some chewed up insulation. I pushed a vacuum hose in a few feet, and I could hear it suck up some stuff.

Now, I'm noticing a sweet "grain" type smell coming out of the ducts. It's not foul or objectionable, but it's a smell that I associate with rodents, and I don't like it. The stuff the vacuum pulled up smelled very strongly of this.

Note that we only run the furnace for about 10 minutes a month to keep things working. We use wood heat the rest of the time. However, air flows slowly out of the ducts all the time (cold air -- a separate problem).

Any suggestions on how to fix this?

Option 1 is to go into the claustrophobic, dirty crawlspace, unhook the vents and try to clean stuff out somehow.

Option 2 is to hire a duct cleaning company like TheFed's.

Option 3 is to run the heat, and hope that whatever smells will dry up and stop smelling.

Suggestions? Thanks!

 

[ls99]

Depends. You have more time or money?

The third option not likely to remove the source of the problem, but will minimise it, such as creating a dried out dead mouse..

On the plus side, if you dig into it, you might find where the critters got in. In any case wherever you can get to it sealing the the ducts with mastic would eliminate some of the leaks, which is a good thing.

Some of the airflows in the ducts are thermal siphoning. Only way to stop that is to block all vents, supply and return.

Happy hunting.

 

[calmloki]

Plastic flex duct under the house? That's most common. I'd opine that Mr. & Ms. Mousey chewed their way in from the outside of the duct, collected insulation from between the outer and inner shells, and started to set up housekeeping in the inner duct shell. That means you probably have holes in inner and outer shells which means you blow hot air out into the crawl when you run the heater and potentially blow fiberglass insulation into the living space. I'd say you are looking at finding the entry hole(s), cutting the duct open at that point, and rejoining with a metal sleeve.

Cut outer shell, pull back w/ insulation from inner shell, cut inner shell, insert metal sleeve, use giant zip-ties on cut ends, use the best duct tape to seal shell to sleeve, pull insulation and outer shell over sleeve, use zip-ties and duct tape again. Or spring the +-$60 for a 25' box of flex duct and replace the bad section. Been a while since I've bought a box of flexduct - probably lots spendier. Having the blower running will aid you search for the entry holes....

 

[Nords]

Now, I'm noticing a sweet "grain" type smell coming out of the ducts. It's not foul or objectionable, but it's a smell that I associate with rodents, and I don't like it. The stuff the vacuum pulled up smelled very strongly of this.

Is it grain-fed rodent [-]hantavirus[/-] urine?

How big are your ducts? Are you able to clean them yourself with a foxtail or one of those 4" diameter bristly dryer-exhaust brushes attached to a broomstick or a fish tape?

 

[TromboneAl]

I think that's exactly right, Calmloki. I'll go down there tomorrow -- it's a real dirty job, and it's tough just getting in there.

IIRC the ducts are more like 10 inches or more in diameter.

I'm inclined to replaced them with unchewable metal ducts.

Is it grain-fed rodent hantavirus urine?

I thought the same thing, but there is no urine component to the smell.

 

[calmloki]

Wonder if you can add some sort of persistent smoke to the inlet and block duct runs to isolate the problem duct run? Minimizing the crawl would be A Good Thing. finding the little mousy hole in the dark on your back will be a problem - if you can see smoke squirting out....

 

[travelover]

Al, I'm not sure how much room you have, but I was able to look into my ducts by using my digital camera and shooting flash pictures as far as my arm reached through the register hole. If that doesn't work, there is still the CFB leaf blower idea.

 

[mews]

Our building's plumber was doing some fairly gross survey work with a flashlight and a mirror on an extension pole.

ta,
mew

 

[TromboneAl]

Those are some good ideas. The smell has gotten worse, so tomorrow first thing I'm going down there.

I was able to look into my ducts by using my digital camera and shooting flash pictures as far as my arm reached through the register hole.

You are a genius, Travelover. I just took a series of shots. Here's the worst one:



Caption: The joys of home ownership

 

[samclem]

You are a genius, Travelover. I just took a series of shots. Here's the worst one:

Caption: The Joys of Home Ownership

It looks like the debris is very close to where the camera was---can you clean this up with a vacuum hose?. Then maybe spray everything down with some bleach solution?

Before you crawl under the house, you might want to put a drop-light or a lantern into the duct so you can find any small holes/leaks via the light shining through. Or, push a drop-light under the house with a pole and look into the duct with a mirror (or take a picture without the flash) to see if you can identify any holes.

I always look for an easy way out before doing a project the right way.

 

[TromboneAl]

It looks like the debris is very close to where the camera was---can you clean this up with a vacuum hose?

Yes, and I did that while you were posting. Here's the result:

 

[Telly]

Yuck. I'd find and fix where the mice entered the structure, then I'd replace the flex duct. The inner sleeve of flex duct won't take much abuse.

Just as a point of reference, in 2006 a 10" (that's inner diameter) by 25' long length at Home Depot was $35.98. They also have any take-off fittings, etc. that are used with it. Also gray (not white) giant plastic zip-ties like camloki talked about. For tape, I use the Nashua 324A foil tape. It sticks better than any tape I've used. Has release paper on the back of it. Position carefully, because when it touches, it's on!

If you go sheet metal duct instead, you will have to buy a lot of fittings, do a lot of cutting, sheet-metal screwing, taping, etc. Then, you will have to insulate the outside of the metal duct, with care to make the outer vapor barrier continuous.

I've done a lot of both over the years.

 

[travelover]

You are a genius, Travelover. I just took a series of shots. Here's the worst one:

Wow, good job.

 

[TromboneAl]

then I'd replace the flex duct. The inner sleeve of flex duct won't take much abuse.

Thanks, Telly. Do you mean replace it with the same type of vinyl(?) flex duct? Is there flex duct that is mouse-proof? My ducting from the dryer is all metal, I believe.

I'm also wondering whether the mice can get into the ducts from the furnace (in the garage). The furnace is rarely on.

 

[TromboneAl]

OK, my first foray showed that the duct system looks pretty good from down there. I couldn't find any leaks. I think I would have felt the hot air escaping even from a small hole. The only evidence of mice was at a place where they had chewed on pipe insulation.

Replacing the ducting would be a big dirty job. Seems like professional duct cleaning is the way to go. Any advice, TheFed?

 

[TromboneAl]

It would cost $500 to have the ducts cleaned. They remove the furnace, put on a big vacuum, then work from each register to push debris into the vacuum. This is followed by a disinfectant spray.

To have the ducting replaced with sheet metal ducts would be $2,100.

 

[calmloki]

You don't have three guys who will do anything for money down there? Larry, Darryl, & Darryl? or some wiry youth with a desire for a $100? In the second pic I can see a "Y" pretty close to the register, and, as Joansmithbffr alluded, that section isn't throttled down so it would be a straight replacement. Maybe stick your digital in the other registers and see if you see a bunch of mousey detritus. Betcha the mice stuck to one place mostly.

I was amazed how much garbage was in our new ducts after we got this place sheetrocked

 

[calmloki]

Re: duct cleaning, from another thread

Should You Have the Air Ducts in Your Home Cleaned? | Indoor Air | US EPA

From the EPA -

"Duct cleaning has never been shown to actually prevent health problems. Neither do studies conclusively demonstrate that particle (e.g., dust) levels in homes increase because of dirty air ducts. This is because much of the dirt in air ducts adheres to duct surfaces and does not necessarily enter the living space. It is important to keep in mind that dirty air ducts are only one of many possible sources of particles that are present in homes. Pollutants that enter the home both from outdoors and indoor activities such as cooking, cleaning, smoking, or just moving around can cause greater exposure to contaminants than dirty air ducts. Moreover, there is no evidence that a light amount of household dust or other particulate mater in air ducts poses any risk to your health".
"You may consider having your air ducts cleaned simply because it seems logical that air ducts will get dirty over time and should occasionally be cleaned. While the debate about the value of periodic duct cleaning continues, no evidence suggests that such cleaning would be detrimental, provided that it is done properly.
On the other hand, if a service provider fails to follow proper duct cleaning procedures, duct cleaning can cause indoor air problems. For example, an inadequate vacuum collection system can release more dust, dirt, and other contaminants than if you had left the ducts alone. A careless or inadequately trained service provider can damage your ducts or heating and cooling system, possibly increasing your heating and air conditioning costs or forcing you to undertake difficult and costly repairs or replacements".


my bold

 

[TromboneAl]

There was a little debris in all the ducts I took pictures of (for example, here's another):



If there were more room in the crawlspace (slither space), I'd rip out the ducts and replace them. To give you an example, at one place I had to squeeze under a pipe, and I could only do it after exhaling.

And the ducts go under and over things -- it's a jungle down there.

 

[deserat]

Wow- T-Al - reminds me of Asimov's Incredible Voyage movie Sad thing is those mice sure did leave a lot of fecal matter - YUCK!

 

[Bestwifeever]

It would cost $500 to have the ducts cleaned. They remove the furnace, put on a big vacuum, then work from each register to push debris into the vacuum. This is followed by a disinfectant spray.....

Also from the EPA website about duct cleaning:

Air duct cleaning service providers may tell you that they need to apply chemical biocide to the inside of your ducts as a means to kill bacteria (germs) and fungi (mold) and prevent future biological growth. They may also propose the application of a "sealant" to prevent dust and dirt particles from being released into the air or to seal air leaks. You should fully understand the pros and cons of permitting application of chemical biocides or sealants. While the targeted use of chemical biocides and sealants may be appropriate under specific circumstances, research has not demonstrated their effectiveness in duct cleaning or their potential adverse health effects. No chemical biocides are currently registered by EPA for use in internally-insulated air duct systems (see Should chemical biocides be applied to the inside of air ducts?).

 

[thefed]

wait wait wait. they are going to REMOVE your furnace to clean the ducts? wtf? tell me more about your home...is it a ranch? any basement? only crawl? Ask them why they cant just cut into your plenum or main line!

and how many SF is your home? you can pm me if you wish

 

[samclem]

Just a comment: Flexduct is crappy. The rough inside slows air movement and decreases the efficiency of HVAC equipment. It frequently gets crushed in attics, cutting off or reducing heating/cooling to portions of the structure. It frequently comes apart at the junctions and suffers mechanical damage (e.g. from mice) that causes significant loss of conditioned air. In addition, the resultant depressurization of the building envelope causes lots of other indoor air quality problems (increased moisture, possibly increased radon, possibility of CO backdraft from appliances, etc). The depressurization/loss of conditioned air can continue unnoticed for years--who checks their ductwork for leaks?

The only good thing about it is that it is cheap to install. After that, it is all negative.

 

[thefed]

Just a comment: Flexduct is crappy. The rough inside slows air movement and decreases the efficiency of HVAC equipment. It frequently gets crushed in attics, cutting off or reducing heating/cooling to portions of the structure. It frequently comes apart at the junctions and suffers mechanical damage (e.g. from mice) that causes significant loss of conditioned air. In addition, the resultant depressurization of the building envelope causes lots of other indoor air quality problems (increased moisture, possibly increased radon, possibility of CO backdraft from appliances, etc). The depressurization/loss of conditioned air can continue unnoticed for years--who checks their ductwork for leaks?

The only good thing about it is that it is cheap to install. After that, it is all negative.

AMEN! More and more newer homes have only flex upstairs...and in runs where it is obvious the builder forgot to do something!

recently, i was in a home with CARDBOARD main lines and flex going everywhere....it was a 350k new construction ranch...which in OHIO is a nice home

 

[TromboneAl]

I've set up an appointment for the cleaning ($472). He confirmed that they do indeed take off the furnace. He feels it's superior to just going into the plenum.

He suggested cleaning and servicing of the furnace (extra $72) which I will probably do.

The house is two stories, but I'm only going to do the ducts that are under the house. One duct company said that code requires that those be sheet metal and not flex duct.

I considered replacing it, but we simply do not use the furnace. I run it 10 minutes per month so that it won't feel neglected.

Thanks for all the advice, TF and others.