Off the top of my head. Please add others.
Heated patios with plastic or plexiglass walls
Emmer
By The Way Café
Bar Raval (very busy at night, nicer to visit weekdays during the day)
Victory Cafe
Heated back patios
Bar Piquette
Union
The Three Speed (this patio is not always open, depending on staff and demand, it seems. Call first or have a back-up plan)
Front patios, not sure about heaters (I couldn’t see any today)
BB’s
Pera Café in Kensington has a plastic tent that’s heated. @rstuart and I had lunch on the open patio (4 ⁰C today)
Arch Café has closed its back patio.
By The Way Café (patio open for weekend Brunch, not at night)
Union has sealed up their patio.
I’m a little disappointed, to be honest. It was as the only heated patio I had found that had good food and good ventilation. I will update the CO2 over brunch 
Pleasantly surprised that the back patio at Union had good ventilation (CO2 under 800) throughout our hour long brunch.
Swiss Train Ride (a Croque ) My friend had the Rib Benny.
For Phoenikia.
Thank you!
Krave Espresso has a little heater running. (Chilly)
Annex Espresso Bar has a bench. (No heat)
Liu Loqum has Muskoka chairs (no heat)
Coco’s has a bench and chairs (no heat)
Romi’s has some tables and chairs (no heat)
By The Way Café still has a busy heated patio that is enclosed, and ventilated because there are gaps in the enclosure because of a big tree in the middle of their patio and a gap in the back wall. It is open for brunch and lunch, but not dinner.
Hair of the Dog will have a heated patio once the weather is warmer.
Union’s back patio is unfortunately more sealed than ever.
The food at Union continues to be excellent. I will probably switch to take-out until the restaurant takes down their winter walls and plexiglass that seal up the space.
I understand some other customers at Union complained about the draft. 
It was the one heated patio that has food I like, and used to have good ventilation.
Cafe Diplomatico has open ventilation on their heated patio. Unfortunately, the food is fair.
It looks like Restaurant Pompette is using its patio on warmer days.
Mamakas has tables out and heaters mounted above each outdoor table ready to go. They must be waiting for warm days. Understandably, their patio has heaters but no walls, so it won’t make sense until it’s 12 ⁰ C or warmer. I don’t even know how much sense those heaters without walls make on cold days.
