Our first 32° night and.......

[David from Dothan]

........the single heat lamp in the center of the 10 X 12 kept the greenhouse at 40°. Thinking that I need to run two as the banana tree leaves felt REALLY cold to the touch.

 

[Gail_68]

Hi @David from Dothan read a view links besides watching a view video's and the greenhouse should roughly be between 60-65F

 

[alp]

According to RHS

Bananas need a long and sunny growing period of some nine to 15 months, with temperatures above 15°C (60ºF) to fruit, with an optimum temperature of 27°C (81ºF), followed by a further two to four months for the fruit to ripen. Feeding with a high-potassium fertiliser may help.

Banana Production in Greenhouses

https://conservancy.umn.edu/bitstream/.../Rebecca%20Smith%20-%20Banana.pdf?...
greenhouses would allow northern climates to grow bananas much closer and could ... water, and they can survive in temperatures down to 14° C. Any colder and .... As with any other crop, it's also important to maintain proper nutrient levels.

By the sound of it, you have only got 4c!