If it gets cold, then NO, it’s NOT properly insulated, air sealed, or glazed. Unless you keep the ambient temperature in your house at 55 degrees. Physics don’t change just because of your location.

Put your money in better insulation, air sealing, and glazing. That has a payoff in lower energy bills as well. Number 1 with a bullet are windows. They are holes in your R value. They need to be triple paned, with attention paid to caulking. Plus spray foam insulation. It sounds as though the whole addition was built inadequately and needs to be upgraded.

I hear you, I know the cold you are talking about, we put in triple pane windows and that made a huge difference but make the bench seats out of concrete and run heating cables through them like you would a floor. They are great and the heat radiates as well.

LWO is often correct, so see if you can take any of her suggestions before you try to build heated seats. Might you simply need better heating? Radiant heating under your floors would give you better, more even heat distribution than pretty much any other type of heating. If that’s not what you’ve got, consider installing it in your kitchen (you’ll have to change your floors). My Mainer friends swear by it.

If you have sold yourself on this heated seat idea, maybe start out by installing electric blankets as your banquette “upholstery” for one season, and see if you like having your posterior toasted when the rest of you is chilly. It might not give you the feel you are hoping for. Better to know before you build.

You could use a short baseboard heater on each wall, under open bench seats. The rising heat would warm the bench, and as it dispersed it would warm the people seated. If you don't have 240v to that area, you can use 120v heaters, although they are more expensive to run. Wire them with a switch you can flip when it's time to sit down to dinner.

Just to add... the heating and windows and sealing are fine. It's more like I want an electric blanket for my back in the middle of winter. Or a heated towel rack... in bench form.

Well then try the electric blanket option this season and see how it goes. They make heated car seats, so if you like the feel you could discuss your options with an auto upholsterer. He may be able to install heating elements into your upholstery.

Keep a basket full of Snuggies for family and friends!

I have radiators and am contemplating something similar- it’s pretty straightforward to add seating over those, though!

I also like mama goose’s suggestion of baseboard heaters.

What about using underfloor heating? They make mats as thin as 18" and you could install it on the vertical piece of wood and hardwire into your wall. Check this out: https://www.lowes.com/pd/QuietWarmth-15-Sq-ft-Premium-0-016-in-QuietWarmth-Film/1000613047 We're attempting to something similar in our home in Iowa. And yes, we have good windows and insulation - just want some ambiant warmth around the kitchen table.

Thank you procrastinationqueen for asking this question, and thanks to Heather Friedman for her suggestion. I don't live in Canada but still want a cozy space to read that isn't chilly from the 3x6 window above the bench. It is so annoying when you ask a simple question and people start preaching at you about why your idea is pointless, when there are clearly many of us who desire the same warmth on cold days (notably, your helpful comments were both from women who 'get it'). I'm VERY grateful for HF's suggestion of radiant heat mats and your idea of heating the backs, not the seats (where they heat won't get through the cushions). Problem solved! Thanks, both!

It works! Our electrician installed the thermostat on the wall and we bumped out the backs of the banquette about 1.5" to provide space for the heat maps. It works great!!!