Size the Door to the Dog, Not the Breed Chart
Breed-based size charts on packaging are a rough starting point at best, plenty of Labradors are built differently from each other, and mixed breeds don't fit a chart at all. The two measurements that actually matter are step-over height and shoulder width.
Step-over height is measured from the floor to the top of your dog's front leg where it meets the chest, with the dog standing normally. This tells you the minimum height the bottom of the flap opening needs to clear so the dog isn't tripping over a raised threshold or ducking awkwardly.
Shoulder width (or chest width at its widest point, whichever is larger, often the ribcage on a barrel-chested breed) tells you the minimum flap width. Add roughly 1-1.5 inches of margin on width and a bit of clearance on height so the dog isn't squeezing or brushing the sides on every pass, a tight-fitting flap gets avoided, not used. Most manufacturers publish a sizing chart cross-referencing these two measurements against their small/medium/large/extra-large flap categories; measure your actual dog and match to the chart rather than guessing from weight alone, since a tall, narrow dog and a low, wide dog of the same weight need different-shaped openings.
What Surface Are You Actually Cutting Into?
Where the door goes changes the installation difficulty and cost significantly, and it's worth being honest about which of these are realistic DIY jobs.
Hollow-core interior/exterior doors. The most common install, but a plain hollow door needs a reinforcement or frame kit around the cut opening, cutting a hole in an unsupported hollow door without reinforcing the edges leaves a weak, flexing panel that will eventually crack around the cutout. Solid-core and wood doors are more forgiving but still need clean, squared cuts and the supplied frame kit to seal the raw edge.
Exterior walls. This is a bigger job than a door install. It requires cutting through siding, sheathing, insulation, and interior drywall, then fitting an insulated tunnel or sleeve sized to your specific wall thickness to bridge the gap without leaving a cold, uninsulated cavity. Stud spacing has to be checked before cutting, and brick or stucco exteriors add masonry cutting on top of that, genuinely a job most people hire out rather than DIY.
Sliding glass doors. You do not cut a hole in tempered sliding glass yourself, that's a job for a glazier or specialty installer who replaces one glass panel with a custom insert unit containing the pet door built into an aluminum or vinyl frame. It's the most expensive route of the three, and it's worth knowing upfront that these glass-insert panels are generally less airtight and less insulated than a flap set into a solid wall or door, because there's more metal framing and more seams around the insert. If you're weighing options, wall installs beat glass inserts on both energy efficiency and long-term security, at the cost of a bigger, messier install.
Security and Insulation Trade-offs, Honestly
Any opening cut into an exterior door or wall is, by definition, a breach in that barrier, electronic locking reduces who can get through it, but it doesn't erase the fact that a hole exists. A few honest points worth weighing before you commit to a location and size:
- Oversized flaps sized for a large dog create an opening that's also large enough for a person's arm to reach through toward a nearby lock or handle, which is worth considering for doors near entry locks or side gates.
- Tunnel length matters for insulation. A short tunnel through a thin door loses far less heat than a long, poorly insulated tunnel through a thick wall, ask about the insulation rating of any tunnel/sleeve kit rather than assuming they're all equivalent.
- Weatherstripping and seal quality vary a lot between budget and premium models; a cheap flap with a loose seal will cost you more in energy loss over a few winters than the price difference against a better-sealed model.
- Placement away from direct sightlines to interior locks or valuables is a simple, free security step that costs nothing but a little planning before you cut.
Training the Dog to Use It
Most dogs need a short adjustment period, not obedience-class effort. Start with the flap propped fully open (many doors ship with a magnetic hold-open panel) so the dog gets used to walking through the frame without the flap moving at all. Once they're doing that confidently, let the flap hang free and use treats or a favorite person calling from the other side to encourage a few pushes through, working from both directions. Only lock the electronic entry function on once the dog is reliably using the unlocked flap on their own, introducing the lock (and the very brief delay for the chip/tag to read) before the basic push-through motion is comfortable tends to cause hesitation at the door rather than solve it.
