A landlord has a duty to provide "habitable" premises. You don't say if you the one paying for electricity for the space heaters, I suspect you are. The landlord should give you some way to maintain a comfortable temperature, or you should give 30day notice move on.
The above answer is generalized reply to an question and is not intended to be legal advice or establish an attorney-client relationship with you. If necessary you should meet with an attorney and provide the attorney with all relevant documents and get an attorney opinion or advice on your situation.
I agree with the other attorney.. the issue is what is habitable..you do not give temperatures of what you consider comfortable .. ask them to keep it minimum 68 F in the winter which is with EPA guidelines .. Plus you can always ask..and if it gets unbearable you can probably claim its uninhabitable and break your lease if you want .. but do it right.. write out several letters and send them to your landlord. keep copies so you have records of yhour complaints.
Please note that I answered this question with general knowlege of the law and with limited disclosure from you, my answer does not create an attorney-client relationship and I cannot be held responsible for how you, the asker, use the information provided. If you want to contact me directly and retain my services you may through my listing on this site or at 248-901-0750 or firstname.lastname@example.org.