ᐅ Should an unused basement in a new build be heated or not?

Hello everyone,

I have been testing my heat pump quite intensively lately.
We moved into our new build (bungalow KFW 55, 2016, 220 square meters (2370 square feet) ground floor, 120 square meters (1290 square feet) basement) in April 2017, and now we are in our first winter with the heat pump.

The basement is completely unused. It’s just masonry. What would you do?
Heat it? Not heat it at all and just ventilate briefly now and then? Heat it and ventilate?
I’m worried about mold growth.
I asked five people and got five different answers.
The fact is: heating the basement, even only on level 2 out of 6, would cost an extra 500€ per year in heating costs!
But the fact is also: I don’t want any mold!
So, what do you think?
Thanks for your helpful opinions.

Hi Hundert,
This is not related to the question, but
do you have the floor plan of your 220 sq m (2,370 sq ft) bungalow? I’m interested in how the rooms are arranged and whether there are long corridors.
Best regards

The question is to what extent the basement is included in the heated envelope of the house.
Is the basement insulated against the ground floor or not?
Is the slab insulated?
I would initially doubt the 500€/year figure based on intuition. Or have you already tested this over several years and also considered it with climate adjustment?

The 500€ comes from about 2500 kWh (kilowatt-hours) of additional electricity that my heat pump would require.

But what are your thoughts on this?
Can mold develop in unheated areas?

Not with sufficient ventilation.
But this would be pure speculation overall, since no one knows all the circumstances. Open basement/stairwell, perimeter insulation, controlled residential ventilation yes/no (also in the basement).

By the way, if the heat pump is properly selected and the heating system correctly designed, an additional consumption of 2,500 kWh (2,500 kWh) of electricity would correspond to about 10,000–12,500 kWh (10,000–12,500 kWh) of additional heat energy.
That is initially not plausible.

Hello Hubert

I heat my entire house including the basement (just over 300m² (3,229 sq ft)). The average annual electricity cost for the heat pump over the last 10 years is 700 euros.

Steven