Hi!

Some back-ground info: We bought a 150 year old farm in Norway and are renovating it. The house is made in a log cabin style, with insulation added on the outside in the 70's. It has no energy source at this time (previously it was just electric panel ovens and wood burning stoves). We used an energy advice professional to assess the house and give advice on increasing the energy mark from F to C. This was in some ways a good idea but as we have found out also a poor choice as the criterion is strict in Norway and does not take into account certain building techniques. For example our walls are made from pine logs and are between 25-30cm thick; under the current criteria they have a 0 insulation index. However nearly all old houses in our area are built to the same design, and the owners and local builders laugh at the 0 insulation index.
That been said, the results from the report:
Results before renovation: Heat loss = 1.83 W/m2. K Net energy need each year = 275.52 kWh/m2.
After renovation: Heat loss = 0.49 W/m2. K and Net energy need each year = 133.72 kWh/m2.
The house is 164 m2, over two floors (82 / 82). 2 rooms 1st floor 3 2nd floor, hall and bathrooms in a lean-to.
How would I go about sizing wood burning boiler with a thermal store with these results?
I did some top of the head calculations and thought’s the gasification boiler between 14-20Kw and thermal store between 800-1500ltr, with a 300 ltr DHW (combi thing, running the DHW and rads / underflow heating). UFH only in the bathrooms and hall (approx. 25 m2) and radiators in the other rooms. The radiators would be to keep the house stable, with additional heat from smaller wood burning stoves for when the temp drops to -25 (which it does for only about 2 weeks a year).

What you think?

In my experience the numbers game is a very rough guideline and you should spec well up and over the outcome of it. This will mean you have more storage and have less burns. A lot of energy is wasted getting the boiler started, so the fewer runs the more efficient it will be (plus less smoke each time). Get the most insulated accumulator going. Some are awful. This means your loss will be minimised over a number of days.

You could go for a 30kW log boiler to heat a large room (10kW) and 20kW to a 1000l heat store (with a daily burn in the winter), or you could get a more powerful gasification boiler and fire it up once every two or three days to heat 2000-3000l.

If you were going to have a separate 300l store, wouldn't that be best for DHW only? To ensure you always had enough hot water for a bath/shower?

Another use of a separate store is to have a 'cool' store heated by solar thermal, to pre-heat mains DHW.

Akvaterm is probably your best option given it should ship relatively cheaply to Norway from Finland. They may even be able to provide an instant answer to your query given they probably have experience of Scandinavian buildings.

Posted By: LandsrudThe best advice I have been given was live it for a few years and then decide after you become more knowledgeable about how your house works.

There is merit in this approach.
You can speed up that learning process by doing a few tests. You can get a couple of cheap electric fan heaters and a plug in energy monitor and just measure how much power and energy it takes to heat the place up for different outside temperatures. This will give you an idea how large the heating system needs to be.