Not sure why you think it's a dumb question. Is there an electric outlet in your porch? If so a heat mat in the greenhouse would do the trick.

I just wasn't sure if it's understood that greenhouses, no matter what size, belonged outside. Anyway, I do have an outlet and thought maybe a heating pad (like for your back) might work? Thanks!

You can get heat mats specifically for seed germination. I don't know the electrical regulations in the US but for safety's sake I would use the correct equipment for the job. With a heat mat inside your mini greenhouse you have an electric propagator.

Could you post a photo or link to a picture on the web of what you have. The term "greenhouse" means very different things to different people. Ranging from one of the small 4-5 shelf things with a plastic cover that I see on the Ocean State flyer that while they call it a greenhouse actually isn't one, to a dome used in the garden to a full blown 12 x 40 foot solid wall greenhouse.

How each is used is very different so lets make sure we are talking about the same thing because if the shelf thing is what you have then no it isn't normally used outside.

And as floral said, no you do not want to use a personal heating pad. You need one made for seed starting.

Dave

Dave is right. Greenhouse can mean a lot of different things.

Like I have four of the mini-greenhouses- the four shelf things with removable covers. Depending on what time of year it is, they get used as shelves for seed starting or to hold wintersown jugs outside- or more like coldframes with the covers on outside to help with hardening off plants.

In the past, I have occasionally used a mini-greenhouse in my solarium with the cover on and hot water jugs in the bottom to overnight tomatoes and peppers if the solarium was supposed to get too chill for them. That might be closer to what you are doing. But without a proper heat mat, I wouldn't try using the mini-greenhouse as a home to start seedlings.

Thank you everyone! Yes, here's a pic of what I have. http://www.amazon.com/Gardman-R687-4-Tier-Mini-Greenhouse/dp/B000NCTGQE