I have cats occupying my boiler room. Unfortunately, my cats are climbing all over the place and are often tearing the flexible air ducts which provide the house with fresh air and warmth. Image for reference:

enter image description here

After a while, the holes in the ducts get large enough for them to fit through and the curious critters start exploring the newly found hiding places. I want to keep them from harm's way and I'm also sick and tired of repairing the damage.

Here are a couple of things I have considered/tried:

  1. Replacing the flexible ducts with metal ones - not possible, the ducts are running through some tight spaces and bend very often, and I'm on a limited budget
  2. Buying a more sturdy duct - the image above shows one which is covered by rubber. This helped to some degree, but the cats are persistent and get through eventually
  3. Wrapping the ducts in a hard and slippery plastic foil. Somewhat effective, but also not perfect

How can I prevent the cats from tearing the ducts up?

  • 36
    Install dogs in your ducts. ;-)
    – Cort Ammon
    Commented Nov 8, 2017 at 15:53
  • 3
    sounds like a question for DIY.SE...
    – dalearn
    Commented Nov 8, 2017 at 23:22
  • 3
    How about: Just close the door & keep that cats out of the boiler/furnace room?
    – Xen2050
    Commented Nov 9, 2017 at 3:45
  • 3
    Sounds better than being outside, so that's good. Maybe the boiler & ducts are in a small corner/area, and they could all be closed off with chicken wire / hardware "cloth" (metal mesh)? There's probably other things around the boiler that could be damaged by, or hurt the cats too.
    – Xen2050
    Commented Nov 10, 2017 at 4:23
  • 2
    Last time I heard anyone trying to cat-proof anything: quinndunki.com/blondihacks/?p=3023
    – Federico
    Commented Nov 10, 2017 at 11:13

11 Answers 11


You could use chicken wire or some equivalent to wrap the duct work. You can get it with gaps of different sizes and it should be available at most local hardware stores. If the gaps were small enough, that should prevent them from even touching the ducts. With larger gaps, they may be able to scratch the ducts but will not be able to pass through the chicken wire to enter the ducts.


  • 2
    I haven't seen chicken wire that's small enough to keep out a cat paw. If they're after them anyway what you want is hardware cloth. Rather than the hexagons of chicken wire it's a square grid and it comes in smaller meshes. It's also a lot stiffer than chicken wire, it will hold a shape you bend it into (but probably not if a cat jumped on it.) Commented Nov 9, 2017 at 2:06
  • @LorenPechtel Do you mean real cloth, or a metal grid/mesh? (Google thinks it's metal). I'd think twice before wrapping air/heat ducts with real cloth. Even if the plastic duct isn't very flammable, the cloth might be, and something like that could be a reason for insurance to deny your claim in case of a fire too
    – Xen2050
    Commented Nov 9, 2017 at 3:44
  • 4
    It's called hardware cloth. It's not cloth at all but a fine metal mesh, e.g. acehardware.com/family/index.jsp?categoryId=1302712. It's essentially just finer mesh chicken wire.
    – JeffC
    Commented Nov 9, 2017 at 4:05
  • 5
    @Carl Insect screen is going to be too easy to cut/bite/scratch through. The chicken wire and other wire mesh will be more durable.
    – JeffC
    Commented Nov 9, 2017 at 4:58
  • 1
    @JeffC It's similar to chicken wire but chicken wire is simply twisted together into a hexagonal mesh, hardware cloth is actually welded into a square mesh. Commented Nov 10, 2017 at 2:25

From a cat's perspective, ductwork is fun! The foil wrap makes cool crinkly sounds when you pounce on it, and it tears easily under the outstretched claws of any cat.

However, cellophane packaging tape is not fun. Booo!!!

Whenever my cats take to scaling or scratching things I'd rather they not (furniture, rugs, door jams, etc), I just cover the spot with a few strips of packaging tape. Something about the plastic-y, smooth membrane seems to really turn them off… and they never touch it again (and I can remove it once they move on to other adventures). I used to wrap things sticky-side out, but that doesn't seem to be necessary — they just hate the stuff as is.

Try wrapping a small section of your ductwork in cellophane packaging tape to see if it deters them. It isn't very expensive, so for a modest investment, I think this has a pretty good chance of deterring the scratching — and will even increase the insulating properties of your ductwork a bit!

  • 15
    One of our cats not only loves cellophane tape, she will even try to eat it given any opportunity :-/
    – psmears
    Commented Nov 8, 2017 at 15:47
  • @psmears same with my cat. He also likes tearing the tape off of packages and eating that.
    – user22794
    Commented Nov 11, 2017 at 20:52
  • @AytAyt: Same with mine... somehow I'm glad ours is not a one-off!
    – psmears
    Commented Nov 11, 2017 at 21:57

If a solid casing like Robert Cartiano suggested isn't practical, you could enclose the ducts in hardware cloth:

hardware cloth example

Hardware cloth is flexible enough that you can shape it as you need to, but rigid enough to support cats climbing on it and keep them from tearing the ducts. You can also cut the hardware cloth to whatever odd shapes you need, and use a set of special J-clip pliers and a pack of J-clips to bind the edges/corners. One of the nice things about this is, if your duct goes behind pipes/etc you can cut holes in your "cover" so the pipes can poke through but the duct still gets continuous coverage.

(Note: I do not use or endorse the products I linked here, they were just the first ones I found on Amazon, to give an idea what I'm talking about)


  • Durable, should support cats' weight
  • Cats may not want to walk/climb on the mesh in the first place
  • Can be cut/bent to fit where and how you need it


  • Expensive (a 10 foot roll of 23-gauge cloth is ~$15, the pliers are $10-20, and clips are a couple bucks)
  • While usually made from galvanized steel, in particularly damp environments hardware cloth may rust over time
  • Time-consuming initial setup (cutting the hardware cloth to shape, and clipping the parts together)
  • Pointy bits won't be fun to brush against; though these might deter cats too

Alternatively, you could combine both methods: use plywood or drywall to protect long and/or relatively straight exposed lengths of duct, and just use the hardware cloth to protect the ducts where they go around/under obstacles or take weird bends. Hardware cloth lends itself pretty well to being stapled to stuff (with a staple gun, not an office stapler!)

  • 4
    "Pointy bits won't be fun to brush against; though these might deter cats too" HA! I had a lot of hardware cloth in a garden of mine and the cats liked to comb their fur on the pointy bits. See: you can't out-cat a cat, above.
    – Tim Nevins
    Commented Nov 8, 2017 at 22:29
  • 2
    This is exactly what I used to keep cats from getting places they should not in utility areas of the house. I used a roll of this stuff and a basic spring-powered staple gun and years later, no problems. I definitely recommend wearing gloves and safety glasses (it loves to sway and spring around when cutting) when handling it, and bending the edge to keep the sharp pointy bits safely away from the side where the cats are.
    – user2021
    Commented Nov 9, 2017 at 4:43
  • 1
    @Snowman Yeah, if I care about the pointy bits I simply fold the edge over. It's never been a problem. Tinsnips can also cut it to merely a bit scratchy, not pointy. Commented Nov 10, 2017 at 2:28

You could try semi-rigid dryer ducting:

dryer ducting It's still flexible, more durable, and only slightly more expensive. This is more than just tinfoil. Besides being stronger, it may also deter them due to the harsh tactile nature of it.

In dryer months (no pun intended) this can act as an electrical ground, too. I've seen cats playing on a carpet get statically charges, then go near an outlet to get zapped. Hilarity ensues (for the human).

If there's any significant amount of heat going through these, I'd stay away from the packing tape @Robert Cartaino suggested. The packing tape could melt and/or start a fire. Putting the tape as a barrier (without actually touching) to getting access to these might be an option, though.

  • 1
    The O.P. kind of ruled this out in his question: "Replacing the flexible ducts with metal ones - not possible, the ducts are running through some tight spaces and bend very often, and I'm on a limited budget." Commented Nov 8, 2017 at 19:17
  • 4
    This is still flexible and not significantly more expensive. This can be bent in the same ways as the plastic and tinfoil ones, except for the really tight turns that should be avoided anyway for airflow reasons. Commented Nov 8, 2017 at 20:48
  • @BrettFromLA even flexible ducts are metal - OP implied rigid metal ducts are not an option, which makes sense considering the effort of snaking them both through tight spaces.
    – user2021
    Commented Nov 9, 2017 at 4:38
  • 1
    This looks like it could work. I've seen these tubes in the past but did not realize I could use them.
    – JohnEye
    Commented Nov 9, 2017 at 16:07
  • @computercarguy The first time I read the OP's question, I just read "metal ducts". But you're right, he did say the problem was that they (RIGID metal ducts) wouldn't be able to snake around. He would need to pay to replace them all, and he's on a limited budget, but it probably wouldn't cost much - and it would solve his kitty problem! Commented Nov 9, 2017 at 17:18

enter image description here

Your first (and best) line of defense is physical barriers to encase or block the duct work. The photo above is faux wood made specifically for that purpose, but you can just as easily (and more economically) fashion a simple conduit or barrier out of plywood or even inexpensive drywall sheets — they very easy to cut and finish to blend in with the existing architecture.

  • 2
    I'm afraid this is too complicated for me - the existing duct is tangled up within a set of other ducts and pipes, needs to be squeezed to fit between a wall and a pipe, has several bends and ends up being fitted to an oval connection on a ventilation unit. Thanks for the idea though, it's something I'll definitely consider using elsewhere.
    – JohnEye
    Commented Nov 8, 2017 at 14:41

There are a lot of products specifically designed to deter cat from climbing, biting, and scratching on the fixtures around your home. Bitter apple is a particularly nasty substance; if you've ever touched it, you'd know what I mean.

For a few dollars, this is an inexpensive way to see if such irritants will (safely) deter your cats from making a playground out of your duct work permanently.

Product Search: Bitter Apple Cat Repellent

  • 4
    I have tried these products and unfortunately, they do not really work in the long term. The cats really hate those at first, but habituation apparently works for cats too and after a while, they stop reacting to it, just like cat owners stop noticing the rancid smell of cat urine after a while.
    – JohnEye
    Commented Nov 8, 2017 at 14:47

Cats like both shelter and warmth.

They are interested in your ductwork because of the heat it provides, and if they have a hole, they also have a shelter.

Place multiple carton boxes around/on top of the ductwork, this gives them an instant shelter that both has heat and protection.


Replace the flexible ducts with insulated flexible ducts. If they rip the outer plastic, they will only hit the insulation and not create an air leak. You can tape up any holes without compromising the integrity of the inner duct. It's essentially a tube inside of a tube with insulation around it.

Insulated Flexible Duct R6

  • 1
    OP would have to use a smaller diameter inside tube, restricting the air too much. Also, this would only slow the cats down by an insignificant amount of time as they continue to dig into the soft sides. Cats will dig through insulation. Commented Nov 8, 2017 at 20:50
  • As @computercarguy said, this is not a good idea. We have some ducts which look like this and guess what, the cats actually love the additional material to play with.
    – JohnEye
    Commented Nov 9, 2017 at 16:06
  • @computercarguy the inside tube won't need to be made smaller, you match up to the interior tube not the exterior one, Commented Nov 10, 2017 at 6:14
  • @Harper, the OP said it was a tight fit in places, so the outside diameter would have to be small enough to get into the same places. This means the inside tube would have to be smaller to accommodate the extra insulation. Commented Nov 10, 2017 at 16:42

Plastic trellis from the local hardware store will solve the problem.

It's cheap and easy to use.

It can be easily cut with normal scissors and still sturdy.

We use one with a 10mm square hole to hang flexible duct (donkey dick in the trade) all the time.

enter image description here


There are many good answers here about protecting the ductwork. An alternative would be to make it inaccessible to cats. That is, remove anything around it that would allow them to climb up to it.

Without knowing how your boiler room is set up, I can't be sure this is an option. But if there are ladders, chairs, cabinets, etc. that give the cats access to the ducts, it may be possible to move them away from the ducts and solve the problem.

  • 1
    Cats are pretty good jumpers despite all the YouTube videos of them jumping for things and missing. This might be as difficult a proposition as squirrel-proofing a bird feeder for just that reason.
    – FreeMan
    Commented Nov 8, 2017 at 18:15
  • 1
    @Freeman Right. I wanted to put it out there just in case. If the ductwork is 6 feet off the ground, and there's nothing to climb on within 10 feet of it, my answer might be an option. Commented Nov 8, 2017 at 19:16
  • Unfortunately, the cats are excellent jumpers and will get anywhere they want.
    – JohnEye
    Commented Nov 9, 2017 at 16:04

Revisit what those ducts are doing. You may see a maze of ducts, but generally they are only two ducts: hot air to the rooms, and cold air return. Often the cold air return is absent, or these particualr ones are unnecessary, leaving only the hot air ducting.

Rather than redundant routes back to the furnace, that whole area can be boxed in, creating a plenum, with each branch then tapped off the plenum. A simple rigid duct to the furnace proper and you're done.

  • Ther are four: An intake of air from outside of house, an intake of warm air from the room with a finnish fireplace (or masonry heater, whichever term you prefer), an intake of "dirty" air from bathrooms and the kitchen and finally one duct which dumps this air outside after recuperation. So it's not so easy.
    – JohnEye
    Commented Nov 10, 2017 at 15:03

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