Piece of wire screen, thin sheet of metal. They have dryer vent covers, didn't your vent have one? If you mean the inside hole anything cold be used. Plastic, masonite, anything you and screw to the wall.

Will you need to block both the inside and the outside? On the outside, it would depend on what kind of siding you have. On the inside, you just need to block up the hole. Sheet styrofoam cut to size could be wedged into the hole and then sealed off with duct tape. You could use sturdy plastic to cover the hole as well, like from a plastic notebook. Even an old linoleum or vinyl tile could be used.

Why not just take the first step?

https://www.homedepot.com/p/Wal-Board-Tools-6-in-x-6-in-Self-Adhesive-Drywall-Repair-Patch-054-006-HD/100036128

Then you'll be ready for the next thing. It's certainly going to keep them out, inexpensive, and what you need to drywall a hole.

I’m assuming it’s not just the drywall that needs to be repaired but the exterior penetration? I wouldn’t pull out the vent unless you’re prepared to deal with that as well.

Exactly how I’d deal with it temporarily would depend on the location and accessibility, but essentially I’d be looking to remove the pipe at a point close to the wall then stuff with something mice can’t penetrate plus insulation.

Curious why you’re switching to ventless, if venting is available?

Yes, pack it with steel wool . I hate mice in the house.

"Curious why you’re switching to ventless, if venting is available?"

My dryer vent long is very long, it spans the entire length of the garage = inefficient; I often have to run 1.5-2 cycles to get the load completely dry; there's really no other way to vent unless I want the exit to be right outside the front door or roof = no.

That length should be within the specs for a dryer unless the duct isn't hard pipe or has too many turns. Or, has leaks in connections.

You're exchanging a long duct pipe for long dryer cycles. Ventless dryers can be very slow.

I'd move the dryer to a different part of the garage where it can use a short vent run to an acceptable wall exit position.

Rodents can chew through many of the materials some have cited above, including drywall, styrofoam, plastic, and linoleum. I'd cover the end snugly with a sheet metal plate inserted or over the edge. Either way, with no gaps.

"You're exchanging a long duct pipe for long dryer cycles. Ventless dryers can be very slow."

Not necessarily so -- read up on the heat pump dryers.

If you plug the vent hole on both sides I'd make it temporary and removable for when/if you sell the house in the future.

" Not necessarily so -- read up on the heat pump dryers. "

No need. I know how they work - they're heat pumps that produce heat (and cold) using the refrigeration cycle. My comment was what I was told by someone who owns one.

If your ventless dryer is to be used in the Michigan location your username mentions, you'll have VERY long cycles in cool and very cold weather up there when the dryer has to extract "heat" from a cold garage. If it's somewhere else, you won't have that problem but the long cycle comment still applies.

You've already made your decision, so my comment is probably irrelevant, but I just wanted to say that my dryer is vented right outside my entry door and it's really not an issue for me. It's not like I'm running the dryer when guests are expected.

Thr hardware store sells caps for all different sizes of round vent. It just pops over the end of the vent pipe to cover it. This is easier to do this with someone on the outside of the house holding the vent in place while the cap is pushed on.

A few vent screws can be installed to keep the cap from coming off.

Personally, I would not drywall over the vent. Just cap it. Maybe put some cellulose or fiberglass insulation inside before cappig it.

That way if the house is ever sold in the future the new owner will have the option of using it.

I own a Miele heat pump dryer in Wisconsin and have almost 10k hours on it over five years of heavy use. Non-towel loads are almost always done in under and hour if they are spun out on high speed in the washer. Towels are done in under 90 minutes. I would have zero worried about a ”good” heat pump dryer. We have been been very happy with our Miele.

"If your ventless dryer is to be used in the Michigan location your username mentions, you'll have VERY long cycles in cool and very cold weather up there when the dryer has to extract "heat" from a cold garage. If it's somewhere else, you won't have that problem but the long cycle comment still applies."

My laundry set-up is in the house. The vent pipe runs out of the house down the entire length of the garage wall. I highly doubt the cycle on the ventless will be any longer than the cycle time now due to the inefficiency of what I've got now.

.

Regardless, it's irrelevant at this point -- the machines are bought and paid for, it's just a matter of scheduling a delivery date.

"We have been been very happy with our Miele."

Good to hear; that's what I got.

" Towels are done in under 90 minute "

I'm also a big Miele fan but not for this product.

My two different gas dryers can finish a load of towels in less than 45 minutes. You're right about the spin cycle playing a big role but 90 minutes is an example of what I was alluding to, a time far beyond what most would consider to be reasonable. If you're happy,, then fine.

Clothing not cooked to perfection is part of our requirments in a heat pump dryer.

That's a good practice. We use nothing higher than the medium setting, never high, and often the low setting too. We use the cool down feature at the end of cycles.

I have to wonder in pork chop's situation that maybe there's a louvered vent opening to the outside that doesn't open so far down the line, or other issues with the dryer, that cause such miserable performance.

The lengthy exhaust path can surely be a factor. No photos or details of its construction have been provided.

My dryer exhaust is at front of the house, although not beside the front door. Doesn't bother me in the slightest, I'm more concerned about the dryer's performance than the aesthestics. It's straight through an exterior wall, so short I can reach through the hood and touch the dryer's blower wheel.