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Mice or Mouse in the HVAC Ducts?

We have yet to discover real rodent proof anything

Researchers have yet to discover an insulating material that will deter mice 100%. In 2011 how can this be? In 1992, the University of Nebraska in conjunction with the Extension service studied the impacts of mice on five types of insulation: Vermiculite, Cellotex, Rockwall, Fiberglass and Styrofoam. They all failed the mouse proof test, that was almost 20 years ago! But, as of this writing, I did one more quick search, just in case something was invented since I began this article (ha ha one day), I discovered I actually did miss something. There is a product that advertises to be "rodent proof" which consists of a reflective type insulation, constructed with a sort of metal-ized film and nylon combination instead of the more common insulation types. So I stand corrected. And, I'd like to point out, I studied the site and they used the same research materials I used in the opening paragraph; not to mention there is a rodent damage disclaimer on the site. So, while this new product may be beneficial and perhaps better than products builders currently use, its still not 100% rodent proof. Okay, mice in the attic and HVAC, on with the show.

The older a structure the more susceptible it becomes to rodent infestation, however new structures are not immune. Insulation, spray foams, tapes, and other synthetic seals or collars are not absolutely rodent proof either. Special precautions need to be taken when the Heating, Ventilation and Air Conditioning ducts become infested with mice. All kinds of critters, including mice, can enter through crawl spaces under buildings or even foundations on slabs; they sneak through the gaps left by connections near plumbing, sewer systems, pipes, phone lines, cable lines, electrical lines, meters, fire places, chimneys, wood stove pipes, gas connections and washer and dryer vents. I’ve even seen mice - all cuddly- in our circuit breaker panel. Another place to check is your HVAC condenser, mice will nest and chew wires there as well. And if the copper is exposed, get it fixed now or you could have worse problems, like a fire!

Making my new home

Flickr via Mukhrino FS
Flickr via Mukhrino FS | Source

Mice in the Attic

Where do mice go after they have got past these entry points? You might not want to know this, especially if you are easily freaked, but, mice live inside the frames of the walls, pantries, closets, in the attic, down to the basement, anyplace really; especially someplace within 35 feet of a food source. Once mice or rats enter the attic they can travel from room to room, or if an apartment, unit to unit. Now, I hear you thinking, "is that what I've been hearing?"

Ever hear things scurrying about above you in the wee hours of the morning? Instead of freaking out, realize this, you can’t ignore it. Some people get used to the sounds and do nothing about it, thinking it’s either their imagination, or its just one mouse. You don’t want to pull down that box of your most prized holiday Christmas ornaments from the attic only to find that Stuart Littles’ cousin nibbled at them.

What has three tails, twelve legs and can't see? Three blind mice. How many mice do you have? Sprinkle a little talcum powder where you think they might scurry in at, along the edge of the walls, then check the next morning, how many little footprints do you see?

Mice Climb vertical walls like Spiderman

Evidence of Mice in the HVAC System

So, if its mice you think you have, how do you confirm they are in the attic hiding in the ducts? I was surprised to hear mice can survive living inside the insulation, after all, fiberglass insulation is hazardous to humans, however mice actually thrive in the stuff. In our first home-30 years ago- we had a crawl space where mice came up at night through the heater vent; I followed a trail of mice poop along the floor boards that led me to a nest under the register. It took three weeks and half a jar of peanut butter to out smart Mighty Mouse and gang. Mobile or manufactured homes have increased exposure with mice as well, adding a skirt won’t help until you have some sort of mouse defense system in place.

Okay, so how do you know those little critters are up there in the ducts-besides the sounds you might be hearing? Your nose may have noticed. Notwithstanding the odors you may smell when the air conditioning or heat system is off, the putrid smells may be more pungent when your system is on. Mice urinate in tiny amounts, but it does produce an odor. Rats on the other hand - a whole different stench - drink so much water, if they urinate above the ceiling, it will eventually produce a visible yellowish brown stain. And those nasty rat odors can travel to the ducts as well. While this article is about mice, and I don’t want to write like I talk-all over the place-you can read about detecting rats here.

A sudden infestation of insects may signal you to mice squatters too. Do you suddenly have flies swarming around in the dead of winter? Blow flies to be exact (moths and beetles included). When I saw a blow fly coming from the vent, and then another, and then another, I knew there was something not kosher going on above my head.

Have you ever seen a mouse nest? It consists of a ball of loosely shredded material, all bound together, two to six inches in size. But since we are talking about the attic, we are looking for nests probably made with insulation. Mice eat it, pee in it, live in it, and have babies in it. They drag it all around the place and tunnel under it too. Upon inspection you may not even see evidence, they tunnel in so far.

How to get rid of mice in your HVAC

I’m not versed in the lingo of HVAC, and being around it, it kinda goes in one ear and out the other, but I do know that the ducts and return system that sends air to your rooms need to be tightly sealed or you are just leaking money as well as air. Besides the damage to the insulation, mice chew wires, break seals and junctions. As my HVAC tech explained to me, the mice damage causes leaks in the ductwork which cause the pressurized air to escape, which can cost you plenty in energy bills or worse, have no working air system at all, in the dead of winter or the heat of summer.

I'm lucky to have an HVAC tech/electrician in the family, but I recommend calling in a professional HVAC tech and an electrician of you think you have found evidence of rodent damage, maybe even a plumber if you’ve found damage in that category. I stress this because, unless you know what you are doing, you may be doing more HARM than good, to your house or yourself. Please research anything you read here first, as I’m just reporting what I observed.

Electrical wires that have been gnawed by rodents could be a REAL fire hazard; if the wire has exposed copper it could cause a spark leading to a house fire. Just taping it over with electrical tape may not be the solution, as the entire section of cable may need replacing. This is not to be taken lightly; I read some news articles about rodents being the cause of house fires. Even more interesting, was a mice induced fire at a cat shelter, now that’s KARMA.

I’ve read two statements in HVAC forums: Duct problems are easier to find than to fix and duct problems are easier to fix than to find. Well guys make - up – your - mind. My son says they are easier to find than to fix because the damage may be hard to reach. We initiated our investigation without his usual tools - because he just stopped by to say hi. Don’t you love people like me!? He’s my son, I can get away with it, and if he wants his favorite White Chocolate Almond Amaretto Cheesecake, welll, I can get him to do anything, even go up it the murky dark cold attic on his day off.

Wet Hand Test

Anyway, he used a flashlight, a wet hand and a 3m dust mask. I peeked my head into the attic entry and let him do all the dirty work. I gave him a spray bottle full of water to keep his hand wet for the duration of testing. With the HVAC powered up and pressurized, he dampened his hand with the spray bottle and ran it above and along the ducts, feeling for air leaks. I was worried he might cut his hand, as there are sharp things around, but he’s a pro so I guess I should quite mothering. It seemed to me that this may not be the safest method, but again, I am an observer. He does normally use a smoke tool, made just for this particular inspection, but they are kinda pricey for a one time test.

What he found was leaks in the junctions, chewed seals, a hole chewed through some plastic part of the duct, insulation in the ducts (nests), and tunnels inside the insulation which we might have missed had we done it on our own. A mouse family was discovered in the end duct where little air flowed, along with mice urine and feces nearby.

Take note of the ducts you encounter; there are several types of ducts used; metal, flex and plastic. Flex ducting is more common that metal, but metal is more expensive and plastic is fairly new, and not as desired as metal or flex. Probably more than you wanted to know, but hey, its free information just laying around my brain.

Duct tape is not for Ducts

Hardware stores carry several different insulation sealing kits for metal, plastic, or flex ducting. Questions to ponder while you are up the attic poking around.

  • Do you repair the insulation?
  • Replace sections?
  • Or rip it all up and start from scratch?
  • Is just taping with duct tape helpful?

Makes sense right, duct tape for ducts – well, you might want to read this article first, Duct tape is the LEAST effective tape for ductwork! What a surprise. Why do we call it Duct take again?

Double edge sword, to vacuum or not to vacuum


If you call a professional, be on guard and check references. My HVAC tech got a service call from a homeowner who complained of a foul smell that got worse when the heat was turned on; she had paid an HVAC company to professionally vacuum the ducts a few days before. While the vacuuming may have helped, they weren’t very thorough. Dead mice still littered the ducts; the mice had eaten poison set out by the homeowner a few weeks earlier, which stopped them dead, but not in a good final resting place.

Some of the rotting carcasses breed bugs, possibly fleas as well. This is just one of the hazards of mouse poison; you never know where the mice will die. And to make matters worse, after believing the vacuum helped, every time the air system came on, she was still breathing feces, urine, rotting rodent carcass, mouse dander, possibly mold, funky proteins, bacteria and other accompanying bugs. If you are susceptible to allergies, beware. This is not a job for a DIY, as the ducts need to be cleaned and disinfected as well.

Some HVAC Professionals and Mice exterminators say cleaning your ducts as a preventative measure has shown inconclusive and more to the point, for the DIYer, vacuuming yourself can cause the situation to worsen by breaking down the chemicals into smaller particles and you wind up inhaling them as you clean. A double edge sword, damned if you do and damned if you don’t.

Does the term volatile organic compound, sound scary? It should. VOC is an industry term for all those nasty things mice (or rodents in general) harbor- including other dangers the EPA considers harmful to humans.


Readers Please Note

Readers please note: I am in NO WAY an expert in the fields I mention, I am only an observer, home owner, and researcher because of my own mouse problems. Please call a professional if you have ANY question whatsoever $6 about any of the situations I write about. One of the reasons I chose rodents as a topic is because I never took mice problems seriously; a few mice, no big deal, right. What I found in my search for the best mouse trap blew me away, grossed me out and freaked me out. What I once thought of as cute and cuddley now give me visions of “Williard and Ben” If you are old as I am, 50, then you are probably laughing or you think I’m insane and I just lost a reader.


Rodent Queens Trick Mouse Quiz

This is gonna freak you out!

Hantavirus Warning

Electronic mouse traps, set along the edge of the areas, are useful for maintaining control, once the ducts are clean and repaired. Make sure you check them often, so they can be disposed of quickly. As much as I dislike snap traps, they do serve as purpose, especially when you run out of money buying electronic traps. Put them in the vent, tying a string to them so you can pull them out, but be careful of the droppings, wear gloves and a mask. The CDC does not recommend glue traps, as the mice urinate and poo in the traps, which can spread Hantavirus, just one of the 35 to 60 direct and indirect diseases caused by rodents.


Comments 6 comments

GmaGoldie profile image

GmaGoldie 4 years ago from Madison, Wisconsin

The Best Mouse Trap,

Anyone who has placed anything in storage can tell of the woes of mice. We placed my beautiful silver leaf mirror in storage and thought it would be fine - wrong. The top has tiny scratches - from you guessed it mice.

Often when storing item away, we go to the supermarket for boxes and the lasting scent of the former contents while not visible to you or I are apparent magnets for our tiny uninvited guests.

You are absolutely correct about the everything - very well done so glad you mentioned the duct tape. I just invested in metal tape and my husband is adding it over the tape we have on our duct work throughout our home.

Dog owners - a special tip - while you may not harbor mice in your home because your dog protects your home, do set traps in your garage. Mice want a sheltered structure.

Very well done hub - voted up and very useful. You are an expert in this field.


The-BestMouseTrap profile image

The-BestMouseTrap 4 years ago from The heartland, USA Author

GmaGoldie: Thank you so much for your glowing comments they really mean a lot to me, "expert in the field" even, I blush, but really, personal experience, research and the fact "Mom" is usually the one that finds the evidence.

I wrote a small post on my website last month about mice in climate control storage; here I was thinking about mice affecting storage in my home until a neighbor told me about a mouse infestation at his climate controlled storage facility, it never occurred to me that would be an issue.

Great tip too, about setting traps in the garage, thank you. Mice love garages, favorite spots to enter your home, especially if you leave the door open for any length of time. Look for tiny holes in the wallboard, 1/4 inch is all they need!


neverthoughtthat 4 years ago

i came from the search engine looking for mousetraps that work good but i never thought of that before that mice could be in your heater ducts. now i get something else to worry ebout.


my-favoritethings profile image

my-favoritethings 4 years ago from PA

I just wanted to thank you, i got here by looking for the best mouse traps for kids cuz mine just thinks it toys to play with. I clicked on you r profile and saw you have quite a bit going on and seem friendly and approachable. Can you tell me how you got started at hubpages here? I apologize if this is improper. I'm new here, well really just new to the internet too. Me and my great grandma just got our first computer and I am addicted. But I see people can make money writing about of all things little itty biddy mouse traps. Amazing. Thanks. Accept my apology it I am doing it wrong.


Jorgen8 3 years ago

Thank you for taking the time to right this. I was thoroughly entertained with the side comments!

I feel confident that I eliminated the rats in my house. The electric trap didn't really work so well. So I used snap traps and p.butter with good results. They kept coming. I got angry and came home with a new bb gun (Typical male, I know). I did numerous late night hunting expeditions into the basement. I felt that $20 was well spent after getting half a dozen of them.

Although one of the weirdest experiences I had during this war was trapping a few of the younger rats in a bucket. One evening I noticed a tiny hole chewed in the bag of cat food. Being lazy, I just put the bag in a bucket with an unused litter box upside down on top of it. The next day I realize a rat got stuck in the bucket. Because it was an awkward way he got trapped, I couldn't figure out what to do with him. If I lifted the cover, he would jump out. So I left him there while I thought about it.

Later came back to the bucket and noticed the rat outside of the bucket trying to get it. I must have snuck up on him because I sat there watching for the longest time. Once he got inside bucket, I quickly grabbed something heavy and slammed it on top of the cover to the bucket. Immediately afterwards I hear another rat on the other side of the room. I ran to grab my bb gun and came back. After dispatching that rat, I took a tall garbage can and slowly tipped the bucket over to dump the rats and cat food in. Some other weird things happened while doing that (crafty sob's) but I now realize I'm writing a novel.

I took the garbage can outside to look and bask in the glory. There were 4 rats in that bucket!!

To finish it up, after I relocated the cat food, I cut off their food supply and they were desperate enough to all get caught in the snap traps. The very last rat presented himself the next day, huge old haggard looking rat. When he saw me, he didn't move. It was that look of defeat. After getting hit with the first bb, he still kept moving about. It took the second one to finally put him down.

Now we are rat free but I know they got in the heating ducts. Found your story while researching how to go about cleaning up. 2 story house with a basement... this wont be fun at all.


dagwood01 profile image

dagwood01 21 months ago from Toronto

Some really good reading here.Very useful article I have been cleaning out duct work for more then 25 years . Couple of things that I would like to add is that mouse dropping are extremely dangerous to asthmatics. Secondly I have witnessed so many occurrences of homeowners putting out mouse poison that dehydrates them. What usually happens is that they look for a place to die which is usually a wall cavity or inside the ductwork of the HVAC system. Thanks

http://www.powervac.ca/power-vac-toronto-gta

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