New to Coal and Not Sure How to Regulate House Temp

I don't have photo yet but the stove is 11,000-55,000 BTU out put and I am heating about 1800 squar feet of space was told by the rep the did the install that it would heat the space I was using it for the hopper useage only happens at night durning the day it runs much slower and heats the house to about 85 at night the temp drop to about 65 I do open the damper at night to keep the temp up but it does not seem to help out muchis there anything esle I could do?

The damper closed during the day?
Its 85.
Open damper at night?
It drops to 65?
Keep the damper in the same position as the day and note the results.

the damper is open a little bit durning the day and a little more at night I will try leaving it the same durning the day and night and see what happens