ᐅ Underfloor heating and mechanical ventilation with heat recovery, replacement of standard radiators

phobos schrieb:
The building specification includes a gas boiler. Since the prices and possibly high operating costs of a heat pump still deter me, I will stay with gas. Maybe heat pumps will become more interesting at some point.

How is it with underfloor heating? I once read that you should keep underfloor heating running constantly in winter because it reacts slowly. Is that correct? Does this also apply to KfW xx houses?

Hello,

What types of heat pumps are offered, and what are the price differences? Which possibly high operating costs do you mean? Is your house being built to the Energy Saving Ordinance (EnEV) standard, or better? Many factors matter when comparing offers...
Heat pumps are a topic on their own. Heating professionals often make mistakes here, for example with buffer tanks in ground-source heat pumps or active individual room control, and so on.

Underfloor heating: Due to the system itself, it naturally reacts slowly, but that also has its advantages. Underfloor heating is a radiant surface heating system and provides a nice, even warmth at low flow temperatures. At minus 20 degrees Celsius (−4°F) in February, we had a flow temperature of 33°C (91°F). With regular radiators, you have around 60°C (140°F).
That is correct, reducing the temperature during setbacks (lowering at night or when away) hardly pays off (I believe savings are about 3%). There is a nice self-regulating effect—the entire floor basically acts as a heat storage. You get a consistent indoor climate, especially combined with a controlled ventilation system with heat recovery, since there is constant air exchange. In my opinion, the only real downside is that you cannot have 15°C (59°F) in the bedroom while the children’s room next door is 22°C (72°F).

Definitely install underfloor heating. As mentioned, if it is installed properly, you can always switch to a heat pump later.

By the way: we have a KfW 70 house with controlled ventilation and heat recovery, and a ground-source heat pump. We effectively saved the chimney and the gas connection—however, part of these savings was offset by the permitting fees for the deep drilling. Currently, for a household of four (2 adults, 2 kids), our hot water consumption (showers) is 1.7 to 2.1 kWh per day (24 hours), which is less than 40 cents per day.
I can’t say more at the moment, as we only moved in January.

I hope this helps you a bit.

Best regards...

phobos schrieb:
...In our house design, a controlled mechanical ventilation system with heat recovery is planned to be installed....

The controlled mechanical ventilation system only indirectly relates to the heating surfaces through heat recovery. It does not matter whether it is underfloor heating, wall heating, or radiators! The most important thing is that the space heating demand is met.
The choice of heating surfaces depends on many factors. In extreme cases (poorly to moderately insulated, or very well insulated like in passive houses), radiators are more advantageous; in transitional cases, underfloor heating or wall heating is more economical. The planned heat generator also plays a role. Heat pumps, for example, require low supply temperatures, so in transitional situations larger heating surfaces are usually needed => underfloor heating, wall heating, or often a combination of both.

Best regards.

Cascada schrieb:

What types of heat pumps are offered, and what are the price differences? What potentially high operating costs? Is your house built to the energy saving regulation standard, or better? Many factors are important to compare an offer...

There is no offer yet. This is from a general specification of a certain prefabricated house manufacturer.
The energy standard should be KfW 70 or 55.
By high operating costs, I mean the electricity costs for the heat pump. You really need true experts for that, otherwise it can become quite expensive.

Cascada schrieb:

In my opinion, the only real disadvantage is that you can’t have 15 degrees Celsius (59°F) in the bedroom while having 22 degrees Celsius (72°F) next door in the children’s room.

Why wouldn’t that work? There are probably separate heating circuits. You can control those individually.

Cascada schrieb:

However, this advantage was partly offset by the permit fees for deep drilling.

I’ve also heard that the drilling can be very expensive. Around 15,000 euros is possible. You could heat with gas for a long time for that.
I once considered an air-to-water heat pump, but I have heard too many negative opinions so far.

Cascada schrieb:

Currently, for a household of four (2 adults, 2 kids), we have a daily consumption (24h) for hot water (showers) of 1.7–2.1 kWh, which is less than 40 cents per day.

That only concerns hot water. What about heating, when this actually runs constantly in winter? How high will the consumption be then?

So, we decided on gas heating for two reasons... we don’t like underfloor heating because of the "warm feet" feeling, and a heat pump would have cost us $12,000 more. But, as always, this is a personal choice, and we got a special deal that made gas even a bit cheaper. And a third reason: we love cooking with gas... so we hit several birds with one stone.

So the prices still seem to vary quite a bit.
The drilling (2x60m (2x197 feet)) cost me 4000€ (euros). The gas connection was eliminated, saving about 2000€ (euros), and the standby heating system is also no longer needed!
And the warm floors from underfloor heating come from times when the underfloor heating was running with high flow temperatures!

phobos schrieb:
...By high operating costs, I mean the electricity costs for the heat pump. You really need experts involved, otherwise it can become quite expensive.

What do you consider to be high operating costs?

phobos schrieb:
...I’ve also heard that the drilling can be very expensive. Around 15,000 € or so is possible. I could heat with gas for a long time with that.

Vertical drilling certainly involves significant costs. How high they actually are depends, among other factors, on the required extraction capacity and energy. As long as this hasn’t been determined, it’s just guesswork. There are also other methods of sourcing for brine heat pumps.
You should also consider that with conventional heat generators, such as gas condensing boilers, consumption is always higher than the actual demand. With heat pumps, it’s the opposite! In the latter case, especially combined with photovoltaic systems, heating and hot water can be achieved at almost “net zero” cost.

phobos schrieb:
...I once looked into air-to-water heat pumps, but I heard a lot of negative reviews about them.

That only applies if exact sizing and design were neglected.

phobos schrieb:
...What about heating when it actually runs constantly in winter? How high will the consumption likely be?

This question is meaningless because every building project is absolutely specific. What A consumes does not apply at all to B, even if it were an identical building!