Yes, a kind of 'air lock' chamber sounds like a decent solution. Good seals on the flaps too, with reasonable resistance to entry so they dont flap about in strong wind.

Your current thinking is probably best

tony - Big cats or very small kids? That's a hell of a cat flap!

You kids and your new-fangled Internet stuff Joiner...

Rgds

Damon

That cat flap is your bog standard draught proof one...they aint. They get stuck slightly open, the seals are next to useless, and its the toing and froing that keeps the air flowing in thats the main problem. as for U-values!!!!
I reckon the idea through a wall with twin flaps is best - with the 90degree bend as well!

Posted By: tony. I cant see the purpose of a bend?

To fool the neighbourhood Tom?? ( sorry Tom Foster not you)

Would it ever be worth having a seperate in-flap and out-flap, perhaps side by side? It's the lack of overlap on a door that has to swing both ways that makes them so hard to draughtproof.
These would be easy to insulate and seal with magnetic tape or similar. As long as your cat is strong enough to push it's way in/out!
If I ever get the urge to butcher our back door in that way I'll post a photo.
RobinB

I guess you dont get porches with 90 degree bends but it would stop prevailing winds, as I mentioned they often get stuck slightly ajar so any straight runs with prevailing wind would push right through. My flap takes more of a beating though as its a terrier.

Whilst not yet available, Richard Jessell, the inventor of the draught-proof letter box ('Ecoflap'), originally worked on a pet flap and having spoken with him have found that his 'Petway' should be coming to fruition over the next year or so - see www.petway.co.uk

I have no connection with Richard, other than as a potential customer.

I would be far more concerned about the draughts and lac of insulation that these things bring. Will the new house be well insulated and air tight.

I designed out a letter plate on my house as it proved impossible to get an air tight and sufficiently well insulated one.

Could you have two, one into a storm porch, then another into the house, even if it was only a cat storm porch/air lock that might do the trick. Microchip ones are best to keep out interlopers.

Richard, we have a sureflap microchip reader.
it has lasted 4 years well and resists stronger cats trying to break in. It has just developed an intermittent fault but we'd get another.
there wasn't much choice on the market when we bought it.
cheers
Dave.

I've built a box/tunnel into the wall. I haven't yet decided what to put into it, but I can just block it up to start with. I didn't want to go cutting holes into my brand new and very expensive back door!

Be sure to look at the size of those Austrian units before deciding what to do. A couple of other products you might want to look at are:

http://energyefficientdogdoors.com/Insulated-Cat-Door & http://energyefficientdogdoors.com/air-infiltration-testing

http://www.idealpetproducts.com/ruff.php

@djh - I had found that US website. The door is a bit ugly, but in terms of performance of air tightness it sounds like exactly what I want. The only downside is that it doesn't have a micro chip reader as far as I can tell.

How long is the box tunnel you have built? My wall construction is going to be a face brick, air gap, insulation, breeze block (300 - 325mm). I'm not sure if that would be appropriate?

Posted By: richardelliot@djh - I assume you'd have a cat flap at either end of the tunnel? I've just been having a look at the Sureflap and there is only one door, so I guess I would have to put one at either end of the tunnel.

I don't know. With a traditional cat flap you can just have one door and leave the other end of the tunnel open. So it depends how keen you are on airtightness and insulation. The Canadian product - Ideal's Ruff door - is designed to have an airspace between the two flaps. I don't think I'd try to put two Sure Flaps in - the need to access them to change batteries makes it a bit awkward. But maybe a Freedom pet Pass at one end to get the airtightness and a Sure Flap at the other for access control could be made to work.

Whether you need a chip reader at all is going to depend on where you live and how your cat reacts to other cats - does it defend its territory or invite them in for lunch? Manual control of in-only, out-only, closed or fully open is definitely essential though.

Revolving cat-door?
Down-draught heater like shops?