those windows are basically the same as just having no window at all. Invest in heavy insulated curtains and electric baseboards right below?

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it also sounds like you really need to find a different heat source... electric heat primarily works by blocking cold air from coming in (which is why they are always under windows).

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Sorry you are getting screwed... I don't know what options you have other then broiler/natural gas... but those are going to be expensive as well with those winodws