ᐅ Heating System for Our Single-Family Home

Hello everyone,

We are going to build a townhouse with 160 sqm (1,722 sq ft) plus a basement (https://www.hausbau-forum.de/threads/grundriss-stadtvilla-160qm-bitte-um-tipps.30018/). We are two adults, a 6-year-old daughter, and a baby on the way. We all enjoy long, comfortably warm baths or showers.

Our construction contract includes two possible heating systems in the price. I don't want to start a fundamental debate here about whether an air-to-water heat pump or gas/solar is better. Maybe someone has some insight and can give us advice on what might be more suitable for OUR building project and OUR family situation. I also have some specific questions...

(P.S.: Underfloor heating will be installed throughout the house except in the utility room. We also want a fireplace.)

1. Gas condensing boiler with hot water storage tank (manufacturer Wolf, 4–8 kW, with 300 l (79 gallons) storage volume). Domestic hot water supply is central without circulation pipes. 2–3 flat solar collectors included.

- Is 300 l (79 gallons) enough for us "warm water lovers," or will we run out of hot water by the end of the day?
- What exactly is meant by circulation pipes?
- Are 2–3 flat solar collectors sufficient? Our acquaintances are also four people and have 12.

OR:

2. Air-to-water heat pump (manufacturer Rotex HPSU Compact, 4–8 kW) with outdoor and indoor units. One energy storage tank with 300 l (79 gallons) storage volume.

- Does anyone have experience with this device regarding noise levels?
- I once read that when using an air-to-water heat pump, it is advisable to install a photovoltaic system as well, but that can be quite expensive, right?

Since we want a fireplace, the idea came up to combine a water-bearing wood stove with gas/solar and install a combined storage tank (or stratified storage tank?). What additional costs would that involve? Does anyone have experience with that?

What would you recommend? Thanks in advance!

Bauherrin92 schrieb:

1. Gas condensing boiler [...]

- Is 300 liters (79 gallons) enough for us "warm shower users," or will we run out of hot water by the end of the day?
- What exactly are circulation pipes?
- Are 2-3 flat plate solar collectors sufficient? Our friends are also four people and have 12.

OR:

2. Air-to-water heat pump [...]

- Does anyone have experience with this device regarding noise levels?
- I once read that with an air-to-water heat pump, you should also install a photovoltaic system, but that’s quite expensive, right?

The storage tank is more than sufficient if you set it to a high enough temperature. At around 70°C (158°F), you would need to mix in a fair amount of cold water before it’s comfortable for showering. If you set it to only 40°C (104°F), the water will come almost directly from the tank to the shower. However, in my opinion, maintaining high storage temperatures is uneconomical. If you plan your house just around a steaming full bathtub, go with gas.

Circulation pipes can be omitted in a single-family home; you’ll simply get hot water after about 5 seconds instead of 2 seconds. One less component that can break.

Regarding solar thermal systems, I would only install the legally required minimum; they aren’t very cost-effective. Your friends with 12 panels probably need a 1000-liter (264 gallons) storage tank to handle the excess heat generated in midsummer.

Photovoltaics is a general topic and should not be directly linked to the air-to-water heat pump. The heat pump usually starts early in the morning, typically before any sunlight hits your roof. For a townhouse, the roof pitch is often quite shallow, and mounting panels on stands doesn’t look very appealing, in my opinion.

Obstlerbaum schrieb:
In a single-family house, you can omit circulation pipes; then it simply takes about 5 seconds instead of 2 seconds for hot water to come out of the tap. One less component that can break.

Thanks for the clarification!

Obstlerbaum schrieb:
With solar thermal systems, I would only install what is absolutely required by law, as it’s not very economical. Your acquaintances with 12 panels probably need a 1000-liter (264-gallon) storage tank to handle the heat generated in midsummer.

That’s exactly right 🙂 12 panels and a 1000-liter (264-gallon) tank—that’s why our 300-liter (79-gallon) storage seemed so small.

Obstlerbaum schrieb:
For a city villa, the roof pitch is quite shallow, and in my opinion, mounting panels on supports looks rather poor.

We can choose between 22° and 24°. Based on your comment, would you recommend going with 24°?

Bauherrin92 schrieb:
Exactly 🙂 12 panels and a 1000l (264 gallons) storage tank, which is why our 300l (79 gallons) seemed so small to me.

We can choose between 22°C and 24°C (72°F and 75°F); based on what you said, should we go with 24°C (75°F)?

24°C (75°F) would be better, but with the shape of your roof, there wouldn’t be that much area facing south anyway. Using all three roof surfaces will get expensive again, because most inverters only have inputs for two strings (series-connected modules). If you don’t want to spend the 10–15 thousand right away, you could install a 50mm (2 inch) empty conduit now for future upgrades. Also, consider getting a slightly larger electrical cabinet accordingly.

Obstlerbaum schrieb:
24° would be better, but with your roof shape, you wouldn’t have that much surface area facing south anyway. Using all three surfaces will be more expensive because most inverters only have inputs for two strings (series-connected modules). If you don’t want to spend the 10,000–15,000 (10-15Tsd) right away, you could install a 50mm (2 inch) conduit now to allow for future upgrades. You should also choose a slightly larger electrical cabinet to match.

Oh dear, I realize again that I have no idea about this topic… inverter, strings… all new terms for me 😀 😀

In general, we tend to lean more towards gas/solar, mainly because gas is well-established—I don’t know anyone who has an air-to-water heat pump. I’m also worried about the electricity costs…

If you have no knowledge of the technology and prefer not to deal with it, and you also have a high hot water demand, you should choose gas. Use as few solar collectors as possible, as they are completely uneconomical and are only installed to meet energy-saving regulations when using gas.

I generally find air-to-water heat pumps combined with photovoltaic systems to be better—but you should engage with the planning process and be able to adjust the pump later and understand what you are doing.