Frank,

Yes, that's pretty normal on a sunny day. At night you'll see the inside and outside temps much closer, depending on how insulated your greenhouse is.

On a sunny day in winter you will see a huge temp difference, and on an overcast day, not as much difference.

If you leave the GH up over the winter, will it withstand snowfall?

Two years ago we had a late snow fall in the spring and then it was followed by a bright sunny day with no wind. The temps in the high tunnel rose to 110 degrees at 4 foot high. The ground was cooler, but I had to vent the place. Felt weird to do it, but the spring can bring some weird weather!

Yeah..i've had it up in late Feb until June and then it just got too hard to vent..it was 120F or something insane like that in late May (outside temp was near 90F)... I think if i remember i had an outside temp around 30F and an inside temp of around 90F in early March, but we had good snowcover...

I highly doubt this thing would handle a lot of snow... another reason to probably take it down. I mainly want it for starting seeds...its really easy to put up/take down.

Probably take it down towards the end of this month... Put it back up in late Feb.

I have a solar heat collector that provides most of the heat in winter for my house. It is 8ft by 18ft by 10ft tall on the south side of the house. I just open the door and heat rolls in. Today it was 75F outside and 125F inside with the door closed. So that is the same 50F as yours. If I had the door open it would be about 100F at the top where heat flows into the house.

If the outside high temperature falls much below 50F it doesn't get hot enough to heat the house very well.