The weather is very cold here in the upper Midwest today. The low for tonight is expected to be right around 0F. Boy, as badly as I want a greenhouse, I am sure glad I am not heating one today! I am curious, I am still holding out for a greenhouse and when I do get it I plan to heat it with natural gas. Do most of you use natural gas or another fuel? Do you feel it is efficient? I pay almost $300 a month in electric bills, which includes my home and my grow area in my basement. I have to believe heating a 15' x 30' greenhouse would be more than that.