Too cold for kittens?

Yesterday my heater went out for the second time in 2 months. It was 50 this morning in the house. The 1st time the heater went out it took my landlord nearly 2 weeks to fix it. Now it seems like it is the same problem again. I was worried about it being too cold for the kittens but when I checked on them this morning, all of them were very warm to the touch. I have them in a box that is plenty big enough for them and Butterball and I have a towel over the small square I cut out of the box for BB to get in and out of. It is completely enclosed. Oh, and they are in my bathroom which is really big. Do you think they will be warm enough until the heater is fixed again? We should warm up by next weekend (into the mid 70s). I don't have a space heater or anything that I can put in there with them. I could borrow one from a neighbor, but are they safe to put in there with them? I just worry about leaving one in there because of the warnings of not leaving it unattened and all.

How old are the kittens - I think they can regulate their body temp/heat by the time they are 2 months old - younger then that, you may have a problem. I'd put plenty of towels around them (like a donut bed) and keep them away from drafts. You shouldn't need a space heater.

They are 10 days old tomorrow, so quite young. I will definitely put more towels around them. Absolutely no draft, thank goodness. Tonight should be another cold night too, it will be a low of about 38 (so maybe 45-50 in the house). I'm dreading it!!