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What it costs to heat a SIP house in winter
Why we will not hand you a figure per month, what actually decides the winter bill, and what to ask a manufacturer for a number that holds up.
Published: September 19, 20263 min read
The short answer: the winter bill is not decided by the wall material but by five things: how airtight the house is, what you heat it with, how large and how glazed it is, whether you live there or come at weekends, and how cleanly it was assembled. The SIP panel works on the first of those and on the last. The rest is decided by the design and by how you use the house.
Below: why we do not publish a monthly figure, what to ask for so you get a real number for your own house, and where heat leaks even from a house that was built well.
Why we do not give a figure per month
Because we have no measurements from occupied houses to put on the table, and an invented sum would be an advertising figure. A bill means something only together with four other things: which house it is, which climate zone it sits in, what heats it and at what tariff.
Change any one of them and the number moves. The same house in Baia Mare and on a plateau at altitude do not use the same energy. The same house with a heat pump and with firewood produces two bills that are not comparable, because they are paid in different things. Anyone who quotes you a monthly sum without asking anything about your house is selling you something rather than answering you.
What you can ask for instead is a calculation: the heat loss for your design, with the panel thickness and the windows that are actually proposed. That is a number that holds, because it can be checked.
What actually decides the bill
| What matters | Why | What to ask for |
|---|---|---|
| Airtightness | Warm air escaping through gaps is the biggest loss in a badly assembled house | Who assembles, and what happens at the joints |
| Panel thickness | The thermal resistance of the wall starts here | The thickness proposed and why that one |
| Glazed area | Glass loses more than wall does, however good it is | The glazed area and which way it faces |
| Heat source | A pump, firewood or gas mean costs that do not compare directly | Which source the design allows for |
| How you live there | A house lived in all week is not the same as a weekend house | How the system is set up for each pattern |
The order below is also the order worth looking at them in.
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Airtightness cuts losses and asks for ventilation
A SIP house is airtight, which is exactly the quality that makes it cheap to heat. The same quality makes it dependent on ventilation: stale air no longer leaves on its own through walls and gaps the way it does in an old house.
That matters for the bill, not only for the air. Ventilation without heat recovery throws out the warm air you have just paid for. Ventilation with recovery preheats the incoming fresh air with the heat of the outgoing air, and only then is airtightness working for you in winter. The options and what decides between them are in our ventilation guide.
What to heat an airtight house with
A house with small losses does not need a large heat source, it needs a suitable one. A heat pump works well at low flow temperatures, which means underfloor heating, and that ties back to the foundation: a slab takes underfloor heating differently from strips, and the difference is decided before the pour rather than after.
Firewood stays an honest answer for a holiday house, where you arrive at the weekend and want warmth quickly. In an airtight house any combustion source needs combustion air brought in on purpose, otherwise the ventilation and the fire work against each other.
What we do not recommend is leaving the heat source for later. It is chosen together with the design, because pipe runs, flues and the plant space are drawn once.
Where heat leaks even from a good house
The first loss is glass. A glazed facade looks spectacular and costs you in winter, and on houses with a wall of glass that shows most clearly. We wrote about it in the article on disadvantages without dodging the subject.
The second is junctions and penetrations: corners, the joint with the foundation, the places where services come in. A good panel assembled carelessly loses there everything it gained in thickness, which is why we insist our own crews do the assembly.
The third is use. A house kept cold all week and heated hard on Saturday behaves differently from one kept steady. That is a choice rather than a mistake, but it is worth making knowingly.
How much does it cost to heat a SIP house per month?
There is no universal figure, and we have no measurements from occupied houses to publish. The sum depends on the house, the climate zone, the heat source and the tariff. What you can ask for is the heat loss calculation for your design.
Is it cheaper to heat than an ordinary house?
A well assembled SIP wall loses little, and an airtight house needs less energy to stay warm. What that means in money depends on your heat source and your tariff, so we do not put a percentage on paper.
Do I need a heat pump?
Not necessarily. A pump suits underfloor heating and permanent living very well. For a holiday house, a source that gives heat quickly can be the better choice.
Does ventilation increase the bill?
Ventilation without heat recovery does. Ventilation with recovery preheats the incoming fresh air with the heat of the air leaving, precisely so the heat you paid for is not thrown away.
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