HVAC experts - Is this a serious problem?

Thanks to my neighbor’s curious cat, I’ve discovered that there is a big hole in the ductwork between my cold air return and furnace. The ductwork is in a very tight crawlspace, so I can’t see where the hole is, but it’s big enough for a large cat to squeeze through and come visiting.
I only have a vague idea of how an air return functions, but I do know it’s needed for efficient air movement. How serious a problem is this? Is there a simple fix? The crawlspace is only about 18" deep and I shudder at the thought of tearing up the floor to get at the ductwork.
It is a gas forced air condensing furnace with sealed combustion if that makes a difference

Return plenums may be created through enclosure of joist bays with panning metal or other approved materials. Although an 18" crawlspace isn’t fun to work in, question #1 is how does kitty get into the crawlspace?

After her owner and I lifted the grate and coaxed her out, we investigated. The cover of the foundation vent on the side of the house had fallen off so Sweet Pea came in on little cat feet. You should have heard my Girlfriend’s banshee howl of fury on having her territory invaded.

If the hole is actually in the crawl space (not in a room has either the furnace or a gas powered water heater) than the biggest problem is that some [potentially large] percentage of your return air will be unconditioned.

Your furnace and A/C system is designed to have 80+% of your air recirculated. In most houses the percentage is 100%—meaning all of the air is recirculated and none is taken from outside. (In commercial buildings it is a requirement that some percentage of the air be “fresh” air; air that comes from outside.)

If this hole exists, and if it is from the crawl space, your furnace and A/C will have to either heat or cool air that may be extreme. In the winter, your furncace may have to heat air that is very cold—much colder than it designed to heat. The average furnace is designed to have return air temps of say 65° to 70°, and to produce a 40-50° temp rise.

So…for example return air is typically 70° and the temp at the registers is 110°–a 40° rise. You’re toasty. (assuming propoane or natural gas)

But…an 18" hole is** big.** So your return air is now 45° (or colder…)because you’re drawing a high percentage of air from outside, where it is cold. (I don’t know where you live so the temps may be warmer/colder) With a 40° rise your furnace is now putting out 85° air----quite possibly not enough to heat the house. (these are just examples)

So to answer your question…

  1. This is likely a comfort issue, and may produce very high utility bills. As long as the hole is not in the same room as gas fired equipment it is not likely a safety issue. You may also have more cat or rodent visits.

  2. I can’t see the hole, or it’s access. I also don’t know how handy you are. But an 18" crawl space is not unknown to most HVAC installers. (although they are hated) Just guessing…I would say that it would take an hour or two in the crawl space for an experienced HVAC guy to make the repair—and quite possibly faster if access is not too hard.

Your time may not be too much different if you’re semi-handy. (although the HVAC guy will be more proficient) Get some HVAC “panning” (basically flat sheet metal) from Home Depot, some screws (w/ drill for them…) and some duct seal. (caulk would probably work) Good luck.

Still likely a problem.

The vent on the foundation gives access to the crawl space.

It should not provide access to [inside of] the return air ductwork, unless there is an opening in the return air ductwork.

Hate to say it, but I’d go down there and figure how kitty got in the ductwork.

I was wondering that as well, how does a cat scratch through ductwork. I’m guessing it’s more likely that some rivits broke and two sections just came apart. And like others have said, if your handy with sheet metal screws or a rivit gun, it shouldn’t take too long to fix.

Serious? Yes. Hire a skinny 9-year-old neighborhood boy to crawl down there and fix it. After you learn how to fix it.

You keep your girlfriend in the crawlspace? Man, I’ve just been told I shouldn’t even keep paint cans there!

Girlfriend is my cat’s name and she lives inside the house, but wow, I do have paint cans down there.
Raindog I am pretty handy and I’m small enough to crawl under there, but I don’t think I can force myself to do it. The house is 120 years old and lord knows what’s under there. But if several furnace guys turn down the job or give me a huge estimate, I may need to get over my squeamishness.