Hole in the wall
February 7, 2008 3:10 PM   Subscribe

My mom is thinking about installing a cat door in the wall between the living room and the screened-in porch. How will this affect her heating bills?

She's in a relatively mild climate (central North Carolina), so she doesn't have to worry too much about subzero temperatures. Not sure if it matters, but she'd be installing it next to the doors that lead to the porch, which are French doors, hence not being able to install it in the door itself. The cat who will be using it is pretty small, so a small opening would be sufficient.
posted by Nathanial Hörnblowér to Home & Garden (7 answers total) 1 user marked this as a favorite
It's pretty hard to quantify, other than "if it seals ok, and there isn't a high differential in temperature, the effect will be minimal to not really noticeable".

What sort of answer do you want? It'll let heat out a bit if it isn't insulated and doesn't seal. The better the seal, the less the loss. If she always leaves a window open for ventilation, however, it will likely make no difference at all.

Again, this is almost impossible to quantify.
posted by Brockles at 3:16 PM on February 7, 2008

I think the OP may be asking, in a sense, how well a cat door is likely to seal.

Nathaniel H - can you give any specifics about the type/construction of the cat door she's considering?
posted by amtho at 3:26 PM on February 7, 2008

To really minimize the heat loss, install a double cat door. One in the wall, as planned. A second in a crate with one open side that can be shoved up against the first door with a relatively tight seal around the edge. An insulated box would be best. In the summer you can put the box in the barn, or something. So the cat just has to exit twice, but the air loss is really minimized. With that arrangement, I'd say the impact on heating bills is minimal, and you'll probably lose less heat than you do opening the french doors ten times a day to let the cat in and out.

Another way to save energy: I once had a cat without a tail -- the vet had to amputate it after some kind of scrape he got into. After that, I figured I had an energy-saving cat, since I could shut the door twice as quick while letting him in and out.
posted by beagle at 3:44 PM on February 7, 2008

Response by poster: Amtho, I think she'll consider any type of construction that could be energy-efficient. She's prone to making things herself rather than spending a lot of money on something she could essentially make herself, so it doesn't have to be a "typical" cat door. Beagle, I like your idea of a double door, if she could teach the cat to use it.

Brockles, the sort of answer I'd like would be along the lines of "We installed a cat door and noticed that our heating bills increased significantly/not at all," etc. I think that might be possible to quantify.
posted by Nathanial Hörnblowér at 7:23 PM on February 7, 2008

Well yes, but that sort of answer means nothing at all unless it is directly comparable to your situation. That was my point. Getting a number will mean nothing as you haven't given enough to go on for a representative comparison:

If someone has poor insulation in their house in general, then it will make little to no difference.
If they have a lot of traffic in their house (human, ie doors opening a lot) then the cat flap will make no difference.
If they often have a window open in the same room, then it will make little to no difference.
If they have their heating on extremely high compared to the outside temp, that'll make more of a difference, if they have it on comparatively low, that'll make less of a difference.
Is the cat flap on the side of the house that gets prevailing winds? Or is the relevant portion of the outside of the house protected?
How many cats does she have? One or 10?
Does it open to the outside or a porch?

While you may get an answer of the style that you suggest, it won't actually mean a damn thing without directly relating it to the same style of situation. That was my point. There are just too many variables for you to get a useful answer from your question.

If you were asking for energy efficient cat flap designs (and I like Beagles double door idea) then you should have made that more clear - "How will this affect her heating bills" suggests to me that you would like to know how much this catflap will affect her heating bills.

Crazy of me, I know, to make such an assumption. But as long as you know that any answer as to relative heating bill costs before and after cat flap installation don't actually mean a damn thing in terms of your mum's example, then that's fine. I truly hope you get some great energy efficient cat flap examples, though. Training a cat to go through two flaps rather than one shouldn't be too hard, although I'd expect it'd be easier if the interim section wasn't too small and wasn't dark inside.
posted by Brockles at 7:45 PM on February 7, 2008

Best answer: I've done this. I didn't notice any change in ambient temperature in the house, or higher usage of the heater during winter. When I first put it in, the door would stick open some times, and you could feel a draft in that room, but I just had to refit it so it didn't stick open and things were fine.

Mine is the type with the magnets, so when it falls closed it is pretty securely closed, i.e., winds don't pop it open.

I'm not sure how installing in the wall would have any different effect from installing directly in the door. I would have to imagine experiences with energy usage with a door mounted door would be the same as a wall mounted door.
posted by tdischino at 7:45 PM on February 7, 2008

Well... look what the Google search for energy-efficient cat door dragged in.

That second one looks pretty good.

Not really an answer to your question, except that it looks like there are better options than what I remember seeing at the local Lowe's/Home Depot (I also live in NC).
posted by amtho at 7:53 PM on February 7, 2008

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