Can you install a slab on grade foundation in the Fall and leave it over winter?

Yes, you can build a slab on grade foundation in the fall and leave it till spring if it has been properly protected against frost heave, though it will most likely require additional insulation. I would suggest you consult with the engineer who designed it.

But when were you planning to pour it, and has it already been designed? The other issue with cold weather pours is that the concrete needs to be warm enough to set. With our last demo house we built a slab on grade with the intention of pouring it in the fall but ran into delays and it wasn’t until March that we did it.

So we ended up needing to order heated concrete (meaning use hot water in the mix), and we did an air heated radiant floor by Legalett, so we were also able to heat it immediately, that’s not something you can do with a hydronic floor. I know that their engineers will also be able to instruct you on how to temporarily insulate it for the winter to make sure no damage occurs until you house is built. You can read more about Legalett GeoPassive raft slabs here, I know they supply slab kits across North America. And, our slab was built in Quebec, a little chillier than Boston so you should be good if you go about it right.