Mouse in cold air return

Old 03-10-22, 11:16 AM
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Mouse in cold air return

This was surprising, has me stumped, maybe.

We've been in this house for 14 years, last night changing furnace filters and saw what looked like a tail, it was, a dead mouse in the cold air return. Actually several of them, couple were desiccated but one looked pretty new.

We have never seen any signs of anything in the house, caught a couple in snap traps that I had set in the attic and bonus rooms but that was years ago.

All the cold air returns are inside the exterior structure with a few going up to the 2nd floor. Basement duct is installed below the floor joists with metal covering the spaces between joists to direct air to the duct so that area cant be the issue.

What I'm thinking is the deck between the floors.

House is brick with some vinyl on second floor. There has to be an opening somewhere that they are getting in and then somehow to the wall cavity where the cold air return is and climbing/falling all the way down to the furnace. Cant get to it so not really sure that I have any options to fix.

Any other ideas/thoughts/comment?
Old 03-10-22, 12:03 PM
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As you know, finding the opening is the first step. First I would go through the house and check every register and cold air return. If one is missing or if fins are missing it can create a gap big enough for a mouse to fit though. I suspect though you won't get that lucky and the opening is somewhere out of reach. I have stuck lights and a camera & transmitter onto a RC 4x4 and driven it through ductwork and the joist cavities between floors for inspection. A pan & tilt camera mount is really helpful for looking down side trunks. Luckily I do RC and already had most of the components in my junk pile. There are some inexpensive toys available but I don't know how capable they are but it might be an option to give a try. Especially with a toy I recommend tying some para cord to the vehicle so you can retrieve it should it die or get stuck.
Old 03-10-22, 02:25 PM
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I was thinking something similar because I suspect it's the vertical wall cavities as they transition between floors so a camera lowered down from the register and spun around.

But as noted, even if a spot was found in the wall or floor there isn't much you can do short of opening up the wall!

The other thing I have to do is get the Mr's to give up her bird feeders. Even though they are away from the house over the course of a winter and several hundred pounds of seed, more than birds and squirrels are being attracted to the general area.
Old 03-10-22, 03:54 PM
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I've mouse proofed my house various times, or so I though, but once in a while one still gets in. Nature of the beast, I think.

Is there a basement/crawl space? If so, maybe a mortar joint is open below grade, which offers access.

Old 03-10-22, 08:54 PM
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I've seen problems where they pan between studs or joists and use that as a return "duct".
Old 03-11-22, 03:21 AM
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Check the outside of the house for a vent that you do not is hooked up to something.

Some installers used to install an exterior vent to pull in a little fresh air into the house.
Simply s vent into the cold air return.

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