Hello all,

I have a space of 140 m3 to warm up. 

This space is divided in 6 communicating cells. The walls, roof and
floor are isolated with 2 high density polyurethane foam layers.
The glass opening are in double glazing an represent 5% of the total
surface in contact with the exterior. There is only one door.

What are the kWh needed to keep this house at 20 celsius if the
outside temperature is 0 celsius? At 10c if -40c?
This is to help me to size up the heater I need.

This question is relative to a real situation and the answer have to
comply with real life (including average loss, etc.).
Is there any recommendation for a maximum efficiency?

Thank you in advance.

Not enough information -  what is the R value of that foam? It could
be as little as R-1 or as high as R-50, even more, it makes a BIG
difference. Also, what amount of air infiltration is there? Is the
door an airlock type? or a single door? How often will it be opened?
In the real world what provision is there for fresh air? will you use
a heat exchanger to preheat the incomming air?

Tank you for your comment.
The foam thermal conductivity is 0,023 W/mK.
The box is "quasi" sealed, and there is only 2 controled fresh air
opening. The door is a weathertight type built in polyester sandwich
with no air leak. There is no heat exchanger for the air intake.
There is one contolled air exaust with a power fan which can be on or off.

Well, I understand it's too complicate to comply with real life as
there are maybe too much unknown parameters.

So, can someone help me in finding what theoretically will be the
characteristics of an heater in kWh if these 140 m3 were totally
sealed with foam. Thermal conductivity is 0,023 W/mK (I don't know in
R3, R4?) and I want to go from
-20 outside to +20 inside.