ᐅ Heating System for a KfW70 Multi-Family Residential Building – Complete Confusion

Hello Forum!

We are finally ready to build. The building plot is purchased, the architect’s plans are finished, and we are collecting quotes.

So far, so good – except for one issue that all five providers have answered very differently: Everyone has at least one opinion on the heating system. These opinions contradict each other so strongly that we – as uninformed laypeople – now have no idea what to decide. We might soon have to roll a dice to answer this question.

- The energy consultant says that in a well-insulated house with heat recovery ventilation, no room heating is needed, and a small boiler is sufficient for domestic hot water.
- Provider A says that an air-source heat pump for this huge house is expensive and not economical.
- Provider B recommends a pellet heating system.
- Provider C suggests a gas condensing boiler solution combined with solar thermal.
- Provider D recommends geothermal energy, which A and E advise against because the investment in the risky deep drilling would only pay off after 120 years.
- The idea of a small-scale power plant (micro combined heat and power) was mentioned once but was immediately dismissed elsewhere!

The house:
It will have 2.5 floors with approximately 130 m² (1,400 sq ft) each for living space,
plus 70 m² (750 sq ft) in the basement for practice/office rooms.
The ceiling height is effectively 2.75 m (9 ft).

A ventilation system with heat recovery is firmly planned, as well as underfloor heating.
We would like photovoltaic and solar thermal systems if they prove economically viable.

Regarding online calculators, I
a) don’t feel confident about them,
b) can’t include heat recovery in the calculations,
but the rough values are an annual heat demand of 7,000 kWh and a heating load of 17.84 kW.

What do you recommend? What experiences have you had?

Best regards,
der_Micha

Hello,

der_Micha schrieb:


- The energy consultant says that in such a well-insulated house ...

Meaning?

This information is necessary to evaluate statements A - E; although I am already quite confident – unless you are building a passive house – that I would send the "energy consultant" to the moon 😉

Kind regards

Hello,

der_Micha schrieb:
....b) no option to include heat recovery

Who doesn’t have this option?

der_Micha schrieb:
....but the figures are roughly heating demand of 7000 kWh/year and heating load of 17.84 kW.

Who calculated this, and how?

der_Micha schrieb:
....What do you recommend?

Hire an independent planner who is not tied to sales!

Best regards

Bauexperte schrieb:
These details are necessary to evaluate statements A - E ...

Since the house isn’t built yet and we don’t have any benchmarks, we are exactly facing this problem—that we can’t assess these contradictory statements. Everyone talks nonsense and argues based on their own statements. As a layperson, you end up more confused after each consultation than before!

€uro schrieb:
Who doesn’t have this option?

_I_ have not found this option in the calculators available online. If there is a reasonable tool you know of, I would be very glad to hear about it.

€uro schrieb:
Who calculated how?

Also _I_, using those calculators on the internet—which I wouldn’t trust even a penny.

€uro schrieb:
Hire an independent planner!

Yes, that’s probably the way to go! Are these the building services engineers?
Is there a directory for such independent planners? Or a certificate/seal/association that can be trusted?

It’s simply shocking that here, in a free public forum, one gets more sensible answers than from people who pretend to have swallowed the wisdom of house building by the spoonful in their profession.

Thanks for now

Hello Micha,

der_Micha schrieb:
_I_ haven’t found this option in the calculators available online. If there is a reliable tool you know of, I would be very glad to hear about it.(...)

Direct links are not allowed in this forum, but try searching on Google, for example by looking up “U-value” and “heat demand.”

As far as I know, these tools don’t perform heating load calculations, but they do provide detailed heat demand calculations, including ventilation losses with or without heat recovery.

Regards
Olaf

o.s. schrieb:
......In my opinion, you can’t perform a heating load calculation there, but you can do a detailed heat demand calculation that also includes ventilation losses with or without heat recovery.

I strongly advise against using such “rule-of-thumb” tools! They might be suitable for roughly checking a U-value, but beyond that, their reliability is very low and poses significant risks. Anyone trying to cut costs on necessary precise planning and sizing needs to understand what they are getting into. There are more appropriate areas where you can do work yourself without causing long-term damage.

Best regards