ᐅ Experiences with Retrofitting Underfloor Heating by Cutting into the Floor
Created on: 21 Oct 2025 10:48
J
josephinee
Hello everyone,
Does anyone have experience with installing underfloor heating in an older building after construction? I just read an article (Abendblatt) where they described milling into the floor instead of building it up. It sounded smart – but how does it work in practice?
This would actually be quite interesting for me, as we are currently renovating an older building. The company Nordwaerme, mentioned in the article, is actually located only 50 km (31 miles) from us.
Maybe someone here already has some practical experience?
Best regards, Josephine
Does anyone have experience with installing underfloor heating in an older building after construction? I just read an article (Abendblatt) where they described milling into the floor instead of building it up. It sounded smart – but how does it work in practice?
This would actually be quite interesting for me, as we are currently renovating an older building. The company Nordwaerme, mentioned in the article, is actually located only 50 km (31 miles) from us.
Maybe someone here already has some practical experience?
Best regards, Josephine
Josephine’s question was answered by me purely from a technical perspective.
Moreover, I am familiar from my professional experience with the advantages and disadvantages of various systems.
It is now up to the questioner to decide which future (and importantly: also forward-looking) system she chooses for her residential property.
Just as a note: of course, electricity costs money. But so do gas and oil. Whether the latter will soon be available only in limited supply is something everyone must decide for themselves.
Since the entire cross-section of a wet screed (in a warm water underfloor heating system) must be warmed up, it is understandable that a larger heat input is needed compared to room heating with a foil heating system, which only needs to heat the approximately 10cm (5 inches) thick ceramic top layer.
However, my related comment was not a recommendation, especially since I do not know the specific conditions of the property.
Other respondents also do not know the property and its specifics.
Therefore, answers like “... we also have ...” come with uncertainties.
Why?
Well, in the case of a cement screed that (hypothetically assumed here) may have just been "shoveled in" 20 years ago with poor compaction, any milling attempt to create groove elements would be a total failure, as the screed would not withstand the mechanical stress.
However, investing today in a heating system that (German) regulations might ban in a few years seems to me to merit at least considering alternative options!
-------------------------------------
KlaRa
Moreover, I am familiar from my professional experience with the advantages and disadvantages of various systems.
It is now up to the questioner to decide which future (and importantly: also forward-looking) system she chooses for her residential property.
Just as a note: of course, electricity costs money. But so do gas and oil. Whether the latter will soon be available only in limited supply is something everyone must decide for themselves.
Since the entire cross-section of a wet screed (in a warm water underfloor heating system) must be warmed up, it is understandable that a larger heat input is needed compared to room heating with a foil heating system, which only needs to heat the approximately 10cm (5 inches) thick ceramic top layer.
However, my related comment was not a recommendation, especially since I do not know the specific conditions of the property.
Other respondents also do not know the property and its specifics.
Therefore, answers like “... we also have ...” come with uncertainties.
Why?
Well, in the case of a cement screed that (hypothetically assumed here) may have just been "shoveled in" 20 years ago with poor compaction, any milling attempt to create groove elements would be a total failure, as the screed would not withstand the mechanical stress.
However, investing today in a heating system that (German) regulations might ban in a few years seems to me to merit at least considering alternative options!
-------------------------------------
KlaRa
I need to clarify something here: it is not the screed that requires energy input to achieve comfortable indoor temperatures, but rather the heat or energy loss through the building envelope that makes the input of thermal energy necessary. At this point, it does not matter how the energy input is provided – that is a matter of efficiency, among other factors.
The electric heating described here is, of course, much more direct, but usually very expensive to operate as the sole system in a room or house. Electrical energy is converted into heat at a 1:1 ratio. An air-to-water heat pump, air-to-air heat pump, or ground source heat pump can achieve ratios between 1:3 and 1:5. The installation of such a system is naturally more expensive than electric direct heating. However, it is significantly more efficient. And the (water-based) underfloor heating does not really care which heat generator is ultimately connected. This can be a heat pump, gas, oil, hydrogen, nuclear reactor, etc. The main point is that the water for the heating system is warmed up. This offers the greatest possible flexibility.
Electric direct heating can make sense in houses under certain conditions. However, I do not see those conditions met in the house described here.
The electric heating described here is, of course, much more direct, but usually very expensive to operate as the sole system in a room or house. Electrical energy is converted into heat at a 1:1 ratio. An air-to-water heat pump, air-to-air heat pump, or ground source heat pump can achieve ratios between 1:3 and 1:5. The installation of such a system is naturally more expensive than electric direct heating. However, it is significantly more efficient. And the (water-based) underfloor heating does not really care which heat generator is ultimately connected. This can be a heat pump, gas, oil, hydrogen, nuclear reactor, etc. The main point is that the water for the heating system is warmed up. This offers the greatest possible flexibility.
Electric direct heating can make sense in houses under certain conditions. However, I do not see those conditions met in the house described here.
Joedreck schrieb:
Electric direct heating systems can make sense in houses under certain conditions. However, I don’t see those conditions met in the house described here. Where exactly do you see a described house here at all? – I still haven’t seen my question about the type of building answered.
Joedreck schrieb:
I need to clarify something here: it’s not the screed that requires the energy input to achieve comfortable living temperatures, but rather the heat or energy loss through the building envelope that makes the input of heat energy necessary. If the screed acts as a conductor in heat transfer, its mass also provides thermal inertia. The screed is not heated for its own sake and does not actively demand heat input, but it still retains heat for a while and then radiates it further (and not only in the desired direction). Assuming a heat consumer who wants the heat immediately, inertia is of course undesirable, and ideally Scotty should be able to beam the heat directly. For this reason, I find the suggestion of a “consumer-near” method of heat input (“consumer” in this sense: the proverbial cold feet) quite reasonable.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
You are right: I mixed up a few things, and there is no described building.
Thermal inertia is definitely present in underfloor heating. Many important points (as usual) are mentioned in KlaRa’s post. However, I personally found it not entirely complete for readers who come back to it later, so I added some information.
All heating systems have their advantages and disadvantages with their own characteristics. You have to deal with that anyway...
Thermal inertia is definitely present in underfloor heating. Many important points (as usual) are mentioned in KlaRa’s post. However, I personally found it not entirely complete for readers who come back to it later, so I added some information.
All heating systems have their advantages and disadvantages with their own characteristics. You have to deal with that anyway...
Joedreck schrieb:
You are right: I mixed things up a bit, and there is no building described. Okay, today is a holiday, but once a week a questioner can at least check their own thread :-(
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
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