Facts vs Myths

Do Cat Flaps Make Your House Cold? Facts vs Myths

Q: What's the best cat flap for a cold climate?

In a double glazed home, a dual glaze glass fitting model, because it preserves the sealed unit's insulation; the maxi dual glaze range suits units to 28mm. In single glazing or timber, any well-sealed model performs the same job; position it out of the prevailing wind and use the lock on extreme nights.

Q: My existing cat flap is draughty: do I need a whole new door?

Usually not. On a Catwalk® door the flap and seals are replaceable spare parts, and the door seals like new once replaced. A draughty flap is a maintenance item, not a reason to remove the pet door.

Q: Do glass fitting flaps cause condensation problems?

The door unit seals around the cut-out and doesn't introduce moisture. In double glazing, a properly manufactured replacement unit is resealed at the opening so the cavity stays dry; fogging between panes indicates a unit seal issue for the glazier, not the pet door.

By Pet-Tek Editorial Team · July 2026 · 6 min read

Catwalk pet doors in a rainy-day glass slider and a timber door, keeping the home warm

Quick Answer

No — a quality, well-sealed cat flap does not make your house cold. The flap is a small, gasketed panel that seals shut between uses. The meaningful winter heat loss in most cat households comes from repeatedly opening the full door for the cat — which a cat flap eliminates. In double glazed homes, dual glaze models preserve the sealed unit's insulation.

It's the number one hesitation before buying a cat flap, especially in a double glazed home, especially in a New Zealand winter: "won't it make the house cold?" The short answer: a quality, well-sealed flap has a far smaller effect than most people assume, and far smaller than the alternative of opening the whole door for the cat several times a day. Here's the myth-by-myth breakdown, and the handful of choices that actually determine whether a pet door affects your warmth.

Key Takeaways

A closed, sealed flap is a small, gasketed panel; the meaningful heat loss in most homes comes from opening the entire door for the pet, repeatedly, all winter.
Double glazed homes keep their insulation by using dual glaze pet door models, which seal the unit at the cut-out.
Draughts come from worn or cheap flaps, not from flaps as a category. Seals and flap condition are what matter, and both are replaceable.

The Myths, Tested

Myth 1

"A cat flap is basically a hole in your door."

A cat flap is a hole with a sealed, self-closing panel in it — which is also a fair description of your front door. A Catwalk® flap closes flush against its frame with sealing around the opening, and gravity plus the seal hold it shut against normal wind pressure. The "hole in the wall" only exists during the second or two your cat is passing through. Compare that to the full door being held open while a cat decides whether it's coming in.

Myth 2

"You can't put a flap in double glazing without ruining the insulation."

The dual glaze models exist precisely for this: the sealed unit is closed off around the cut-out, so the rest of the unit keeps insulating exactly as designed, and the flap itself is the only local change. How the sealed unit is handled, including toughened glass and low-E units, is covered in pet doors in toughened & double glazed glass and cat flaps in double glazed glass. The body itself is weather-thought-through too: its internal draft angles are shaped so rain that gets driven into the frame drains back out instead of pooling — trapped water is how lesser doors end up mouldy and corroded.

Myth 3

"Pet doors are always draughty."

Draughts have causes: a warped cheap flap, perished seals, or a flap that's been chewed and never replaced. Quality UV-stabilised polycarbonate doesn't warp or go brittle in NZ sun, and every Catwalk® seal and flap is replaceable as a spare part, including on doors fitted 20+ years ago. A draughty flap is a maintenance item, not a life sentence. On a Catwalk® door the gap between flap and body is machined to next to zero tolerance and closed with a full brush seal; there is no daylight around the flap's edge for a draught to use.

Myth 4

"Once it's in, you can't do anything about cold nights."

Every Catwalk® door has a 4-way manual lock. On a southerly-storm night, set it to fully locked (with the litter tray on standby) or in-only, and the flap is a rigid sealed panel until morning. No batteries, nothing to remember to charge.

Myth 5

"A bigger flap means a colder house."

A correctly sized flap seals the same whether it's cat-size or Labrador-size: closed is closed. What matters is the fit and seal condition, not the flap area. Size for the pet using it (per the measuring guide) and let the seals do their job.

The Fact That Matters

The biggest pet-related heat loss is the human door.

Every time you open a full-height exterior door to let the cat in or out, you exchange a doorway's worth of warm air, and in most cat households that's many times a day, all winter. A flap replaces those full-door openings with a two-second cat-sized pass. That trade is why pet doors, done properly, tend to make homes easier to keep warm, not harder; the full argument with practical tips is in keeping your home warm with a pet door.

The Warm-Home Checklist

Position out of the prevailing wind where the layout allows: a sheltered side or porch-protected door beats the exposed southerly face.
Double glazed home? Dual glaze model. Cat and maxi models suit sealed units to 28mm; dog models to 32mm.
Check the seals each winter: a two-minute look; replace worn flaps or seals from spares.
Use the 4-way lock on the worst nights or whenever the cat is in for the evening.
Size correctly: a flap the cat glides through swings and re-seats cleanly; one they push and squeeze through gets knocked out of alignment over time.

Frequently Asked Questions

Do cat flaps make your house cold?

A quality, well-sealed cat flap has a far smaller effect than most people assume: the flap closes flush against a sealed frame, and the meaningful heat loss in most cat households comes from opening the entire door for the pet many times a day — which the flap eliminates. In double glazed homes, choose a dual glaze model to preserve the unit's insulation.

Will a cat flap increase my power bill?

A sealed quality flap's effect is small, and for most households it's offset by no longer opening the full door for the cat many times a day. The homes that notice a difference are usually dealing with a worn or cheap flap that no longer seals; fixing the seal fixes the bill.

What's the best cat flap for a cold climate?

In a double glazed home: a dual glaze glass fitting model, because it preserves the sealed unit's insulation; the maxi dual glaze range suits units to 28mm. In single glazing or timber, any well-sealed Catwalk® model performs the same job; position it out of the prevailing wind and use the lock on extreme nights.

My existing cat flap is draughty: do I need a whole new door?

Usually not. If it's a Catwalk® door, the flap and seals are replaceable parts; order from spares & accessories and the door seals like new. If it's another brand with a warped flap and no parts available, that's the moment to upgrade the unit; the existing cut-out can often be reused or adapted; contact us with the cut-out size.

Does wind blow the flap open?

A correctly seated flap resists normal wind; the seal and the flap's weight hold it closed. In severe exposed-site winds, use the 4-way lock, and consider positioning on a sheltered elevation at install time. Persistent flapping in ordinary weather means a worn seal or misaligned flap, both fixable with spares.

Should I lock the flap every night in winter?

That's a household call: locking overnight maximises warmth and keeps the cat in; leaving it open keeps the 3am toilet trip self-service. Many owners use in-only mode in the evening: the cat can come home but the warm air stays. All three are one turn of the dial.

Do glass fitting flaps cause condensation problems?

The door unit itself seals around the cut-out and doesn't introduce moisture. In double glazing, a properly manufactured replacement unit is resealed at the opening, so the cavity stays dry; fogging between panes indicates a unit seal issue for the glazier, not the pet door. Surface condensation on cold mornings behaves the same as the rest of the pane.

Retailers & Trade Buyers

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