‘Tis the Season To Keep Mice and Rats Out of Your HVAC Ductwork!

David Bennett David Bennett | November 24, 2019 | Pest Control

Last week’s quiz question: Why do rodent teeth never stop growing?

Answer: Rats have incisors and molars (no canines). Incisors are the frontmost teeth in mammals. In rats, these are the four, long, sharp front teeth, two on top and two on the bottom. Rat incisors are highly specialized for gnawing. They are open-rooted, which means they grow throughout life. Enamel formation continues throughout life as well. Molars are the rearmost teeth in the mouth, used for grinding food prior to swallowing it. Rats have 12 molars, six on the top and six on the bottom (and three on each side of each jaw). Molars are never replaced. Rats have only one set of teeth during their life (called monophyodont). 


This week’s quiz question: What percentage of time do rats spend sleeping?


‘Tis the Season To Keep Mice and Rats Out of Your HVAC Ductwork!

It’s colder outside!  Like you, rats like warmth, shelter and food.  HVAC ductwork is certainly warm, and a very inviting home to winter

over in (or stay year-round!)   Just when you think you have rodent-proofed your house, here we are rabbiting on about one more thing you may not have considered!  We’re here to help! Often, people don’t think about opening their air conditioning unit or checking the HVAC ductwork—sometimes people forget about cleaning HVAC ductwork routinely as well which can be a fire hazard if too many dust bunnies accumulate.  Add the health hazard of either dead rodents or their stinky urine and feces, and you’ve got

potential expensive problems on your hands.  One way rodents can enter your house is through your central air unit, bird blocking vents, furnace ducts in your garage, and crawlspace vents.  As we’ve said before multiple times, rodents can squeeze into very small spaces. Now, if they die in ductwork, the odor that wafts through your house may have you moving out to stay in a camper or a hotel until you can get in there yourself, or hire pest control to get in there to see where the dead rodent(s) are. Second, there are health issues to consider.   Dengarden relates a horrific personal story about a client finding rodents in the HVAC, and something to consider if you clean yours out yourself:

“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 caused them to die 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, possible mold, funky proteins, bacteria and other accompanying bugs. If you are susceptible to allergies, beware. This is not a DIY job, 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-edged 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 some that the EPA considers harmful to humans.”   The Centers for Disease Control (CDC) also warns that mice can squeeze through a hole as small as a dime and that rats can get through a hole as small as a quarter.

  • Interior air vents that have louvered, angled or grid openings smaller than a dime in size will likely not allow enough room for a rodent to squeeze through.
  • Fresh air intake vents and exterior air vents can be entry points if they are large enough, are cracked or there are holes in the protective screens.
  • Attic and crawl space vents are also easier for mice and rats to access if not properly screened or covered.

 Let’s talk about each of these potential entry points.  That way, you can, in partnership with your pest control professional, proof your AC now, so you don’t open it up in the spring and find unwelcome surprises later as well as higher energy bills.

Air Conditioners

According to The Exterminators, a company in Canada, “The insulation in air conditioning units often attracts mice, since its warm

and suitable for nesting. Mice can get in through your air conditioner via air vents, pipe entries, block access panels and cable entries. The first sign of mice living in your air conditioner is mice droppings around outdoor air conditioning units, and occasionally you will spot dead mice which look like they have been electrocuted. There are many pests that will invade your air conditioning unit, but mice and rats are the most worrisome. Mice will gnaw on wiring [and refrigerant lines] or build nests that can put a strain on the unit.”   They can chew through electrical wires, damaging the unit, making you go without air conditioning until it’s repaired. Burgesons adds: “ If a homeowner ignores the issue, it could lead to serious structural damage. The result is a loss of conditioned air through the attic meaning the HVAC system will not work at maximum efficiency.”  How to fix this? First of all, if you’ve never opened your AC unit, open it now and inspect it for rodents and rodent damage. If you find chewed wires and refrigerant lines, repairing damage now can save you time, discomfort and money later.  To prevent reinfestation, you can install special mesh AC unit covers for your central air system that keep rodents out. Seal any cracks and gaps in ductwork and cover your vents and flue pipes.  The Exterminators also advises “Moisture buildup around the AC unit is one reason pests, such as mice, will invade the unit. The moisture provides them with something to drink, and hydration is necessary for mice. Prevent moisture by redirecting puddles from rain or condensation that form around the unit. Guard your condenser. Most times, rodents such as mice move into your AC unit through its air vents. Clear all vegetation around the unit including stacked up material near the AC since they could attract mice. Repeat this routine occasionally and through the seasons. You will need to be extra careful during seasons when your air conditioning system is not in use since they are most likely to attack them. If you are unsure of how to go about this, contact your local pest control service to help you out. “

Furnace Ducts in Your Garage

Furnace ducts are the perfect warm shelter for cold rodents.  And because duct work around furnaces is not always properly sealed, rodents can get in.  Redfin.com advises, “ Look at the rear and sides of the furnace for small gaps, or gaps around any plumbing holes going through the wall in your garage.

If you find any signs of rodent activity, contact an expert. Inspect, patch holes in your crawlspace or cut back trees that are touching your house. A trained professional will know how to find the holes to seal to prevent rodents from entering your home, clean out damaged materials and sanitize the area, as well as any other work that is needed to deal with a rodent problem.”

Vents—All Kinds of Vents!

Bird blocking vents allow air into the attic system without allowing birds and rodents into the house.  Usually these vents are covered with some kind of mesh material, but they can get damaged over the years. Regular inspection if you have bird blocking vents is necessary, along with regular inspections of foundations and roofs for any cracks or potential entry points.   Again, we cannot impress enough the importance of eliminating any long branches, vines, or any other vegetation that rodents can use as walkways to get into your home.   Keep the verge pruned back!  Some houses have crawlspace vents located on the outside of your home under the bottom of the siding.   Some homeowners question whether the vents are really necessary and ask if they should just seal them up permanently.  This Old House advises otherwise: “These vents allow outside air to circulate under the floor in summer to prevent the moisture buildup that encourages mildew and rot. In winter, when the air is drier, the vents are closed to reduce the chance that the pipes in the crawl space might freeze. The simplest way to close foundation vents for the winter is to plug them from the outside with foam blocks made specifically for this purpose. Just remember to remove the plugs when the weather turns mild in the spring. As you do that chore, check to make sure that the vent screens are intact so that insects and other critters don’t make a home under your house. Automatic vents are less fuss.  [Some companies make automatic vents that don’t require electricity].  Insofar as heat and air vents go, again, you may have to consult an HVAC tech through your pest control professional to make a thorough inspection and initial removal. However, if rodents have already made egress into your home, this pest control company has tips on how to get rid of them:

How to remove mice from air vents

Your air vents are the likely areas that mice will use as they look for food and a safe place to sleep. While mice often die inside these ducts, they can send a rank odour throughout your living areas. In case you notice you have mice in your air vents do the following.

  • Switch off your AC system allowing the grates to get to room temperature. Remove the grates that are used to cover your heat vents.
  • Bait a snap trap with food that mice love such as chocolates, peanut butter or raisings
  • Place these traps in each air vent.
  • Check the traps regularly each morning using a flashlight. If any mice have been trapped, remove them. Use rubber gloves and dispose of the mice in a Ziplock bag.

Snap traps can also be placed in the vents, which  must be routinely checked and bodies disposed of.   Pest control insulation might be something else to consider. What is it?  Rottler.com explains: “Pest control insulation is a blown insulation that can be applied on top of your current insulation to create a better barrier. Since it is blown, it fills in the gaps and cracks and creates a complete layer that can be as much as a foot deep. It is installed through a slow, meticulous process of moving back and forth through the attic space, pouring out tiny fibers from a hose…The best part about having pest control insulation are the pest control benefits and, this pest control happens in a unique and clever way. The fibers of pest control insulation have borates that kill pests over time. For animals that have a liver, the borates can be processed. But bugs don’t have livers. So, these borates build up until it is fatal to those bugs. That means termites, silverfish, cockroaches, wasps and other harmful pests are not going to find safe haven in your attic spaces. And, though it isn’t guaranteed to stop wildlife pests, like mice, rats, and squirrels, these creatures will not feel welcome in an attic that has pest control insulation–and they definitely will not want to make their nests out of it.”

Exclusion (including our RodeXit proofing strips) with your pest control professional is the best line of defense against rodents, for health of you and yours, saving money and preventing on going issues with rodents gaining entry, in edition to making your home more energy efficient.



Standard Pest Management RodeXit Testimonial 

Review recent RodeXit testimonial by Josh Bloom from Standard Pest Management, company and crew. Providing excellent service to their community and customers in area they service. They were an early adopter of RodeXit proofing strips and we are proud to have them as customer of our Fenn traps also.




RodeXit Solutions to Problems


  • Scientifically designed, tested, proven for protection against Mice, Rats, Bugs, drafts, higher or lower outdoor temperatures.
  • Flexible material with embedded with 1mm thick stainless-steel wires 5mm apart too narrow for even a mouse to penetrate.
  • Fast mounting, quick, simple, easy to install, handle and manage. Roll/coil in a box
  • RodeXit proofing strips are used for doorsweeps and more in the Food industry, Public housing, Warehouse, Residential, IPM and other applications that require exclusion. 



Tags: CAPCA, Center for Disease Control, Eco Friendly, Exclusion, Fenn Traps, Food quality and safety, Integrated Pest Management, IPM, Leeds, Multi family housing, NPMA, NWCOA, NYPMA, PCOC, Pest management, Pest Proofing, Property maintenance, property management, Property managers, Public Health, Public housing, Quality Assurance, Rodent exclusion, Rodexit

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