ᐅ Water-heating wood stove (supplementing the air-to-water heat pump and mechanical ventilation with heat recovery)?

We are building a house of about 185 m² (1991 ft²) with 36.5 cm (14 inches) aerated concrete walls, aiming for KfW70 energy efficiency standard (I can provide data later, but that’s not the main point here).

In addition to a controlled ventilation system with heat recovery (probably a Zehnder, based on recommendations), the primary heating will be an air-to-water heat pump (Buderus). However, it is certain that we will also have a fireplace in the living room (for atmosphere, the enjoyment of a fire – the primal instinct of man, cozy fast direct heat, etc.). A side benefit: when the air-to-water heat pump becomes less efficient in winter, I like to burn some wood, usually self-collected from our own forest plot.

Now, the idea was to use the heat from the fireplace to warm the entire house by installing a hydronic (water-bearing) stove like the "Wodtke Tio," instead of a conventional fireplace stove. For this, the buffer tank would be increased from about 300 liters (79 gallons) to 850 liters (224 gallons), according to the initial (unverified) estimate by the heating engineer.

According to the manufacturer: "With a water-side efficiency of approximately 70% and a nominal heat output of 8 kW, the Tio heats the room where it is installed and simultaneously the buffer tank."

Would this be a good idea? (Additional cost including installation roughly estimated at 5000 euros compared to a standard fireplace)

Wastl schrieb:
Including the hydraulics, the larger storage tank, and so on?

Yes, everything included (I also have a friend through whom I can get such things at a lower price).

Wastl schrieb:
... I doubt you will actually achieve any economic benefit from it.

That is exactly the question..... I cannot really assess to what extent there will be any savings. Or whether it might at least offer advantages in terms of comfort (no overheating of the room, since 70% of the heat goes into the water).

Hello Frank,

FrankDr schrieb:

.... primal instinct of man,

With all respect for your secret wishes – you are using a sledgehammer to crack a nut. Nowadays, there are also smaller wood stoves that satisfy the occasional desire to "watch the crackling fire."

You are about to spend a lot of money on a myth; the "extra electricity costs" for operating a purely air-to-water heat pump relate solely to defrosting the externally mounted fan at freezing temperatures. This amounts to about 0.02% of the annual operating costs. Of course, it is different if by air-to-water heat pump you mean an exhaust air heat pump as offered by the red competitor. Aside from the fact that I would never install or recommend that, I would advise you to base your heating concept on the heating demand of the new building to be constructed. There are specialists who can compile the suitable technology for you so that demand and operating costs match in the end.

Best regards, Bauexperte

If your efficiently operating and properly planned air-to-water heat pump is installed, I would advise against using a secondary heat generator (except perhaps a small decorative stove). The originally mentioned 300 liters (about 79 gallons) – is that a buffer tank or just the domestic hot water tank?

In my opinion, it is much more difficult to connect two heat generators efficiently. For €5,000, you can heat for a very long time. With an air-to-water heat pump combined with underfloor heating, you might even be able to completely avoid a buffer tank.

Best regards

Research monovalent and bivalent operation. There are also air-to-water heat pumps that operate in monovalent mode. In that case, there is no electric backup heater.

Thanks in advance for the advice. I think I'll skip the hydronic fireplace (bit like using a sledgehammer to crack a nut)...

I’m not sure yet which air-to-water heat pump to choose... it will be calculated and recommended directly by Buderus (they offer me such a good discount that I won’t be able to offset the benefits in purchase price and installation costs by going with another company).

As soon as they provide a recommendation, I’ll share the information.

Only the controlled mechanical ventilation system will probably be from Zehnder, as my builder offers and recommends it directly.