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Cutting Holes in Existing Screeds for Underfloor Heating: Depth, Even Heating, & Experiences

agapyta 35550 22
Best answers

Can I cut grooves into an existing screed to add underfloor heating pipes, and how deep should the grooves be to avoid uneven heating?

You can cut grooves into an existing screed and lay the pipes there, but several replies say the better solution is to rebuild the floor or use a renovation system, because grooving weakens the screed and can lead to cracking or pipe damage [#17049932][#17051728] If you do groove it, one installer reported depths of about 2–5 cm, while another suggested shallow grooves of about 25 mm deep and 25 mm wide with PEX pipes, then filling them with Nivoplan Plus Mapei [#17052299][#19822383] To improve heat spread, one reply suggests placing the tubes on a metal mesh and pouring over them, since metal conducts heat better than concrete and can reinforce a thin screed [#17050218] Pipe spacing should be close; one reply says the furrows may be 15–20 cm apart, but then corrects that they should be every 10 cm, and the loop length should not exceed 60 m [#19822383] One user who did this said the temperature difference is small with continuous gas heating, but can be noticeable if the system is heated only for a few hours at a time [#17052299] Also remember that insulation should be under the tubes [#17049932]
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  • #1 17049915
    agapyta
    Level 2  
    Hello,

    did anyone cut holes in the existing screed and lay pipes for underfloor heating? If so, at what depth were the holes cut? I am thinking of such a solution, but I am afraid that the floor will not heat evenly, i.e. only the surface just above the pipe will heat, next to it cold and then another pipe and heat. With the traditional way of laying underfloor heating, the entire surface heats evenly.
    Is it even worth thinking about such a solution?

    I am asking for your opinions / experiences.

    thank you!
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  • #2 17049932
    DriverMSG
    VIP Meritorious for electroda.pl  
    The tubes are placed fairly close together, so if you cut furrows on them, then this spout won't be much. It is better to immediately forge the floor completely and pour a new one.
    Also, do not forget that there must be insulation under the tubes.
  • #3 17050138
    agapyta
    Level 2  
    Thank you!
    the problem is that this is a fresh home and fresh floors, we did not take this into account before and now we would like to 'add some extra' to the floor as invasively as possible. I have heard of such a device as a wall chaser to cut holes in a quick and less invasive way, but before I make a decision I want to know if it makes sense. There is foamed polystyrene under the screeds, there is not only a thermal insulation foil. On the other hand, it's about floors upstairs, so there shouldn't be much heat loss.

    best regards
  • #4 17050170
    Parowy
    Level 22  
    Welcome.

    Consider the electric heating mat, you do not need to cut furrows under it, except for one for the temperature sensor.

    best regards
  • #5 17050189
    vodiczka
    Level 43  
    Parowy wrote:
    Consider an electric heating mat
    Higher operating costs but you can consider. Maybe the author will explain why
    agapyta wrote:
    now we would like to add some extra floor space
  • #6 17050218
    anders11
    Level 30  
    Last week, I witnessed groove milling under
    floor heating.
    The pipes were hidden in concrete about half a cm, but the whole thing was to be covered with a layer of some
    two cm thick.
    For better heat distribution over the floor surface, I suggest tubes
    lay the metal mesh and just pour
    Metal is a much better heat conductor than concrete and will additionally strengthen a fairly thin screed
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  • #7 17050337
    ls_77
    Level 38  
    And how large the surface is to be heated with underfloor?
    What is the room: kitchen, bathroom, hallway or room / living room?
    Is there still other heating, e.g. radiators, or just a floor?
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  • #8 17050505
    agapyta
    Level 2  
    anders11 wrote:
    Last week, I witnessed groove milling under
    floor heating.
    The pipes were hidden in concrete about half a cm, but the whole thing was to be covered with a layer of some
    two cm thick.


    For better heat distribution over the floor surface, I suggest tubes
    lay the metal mesh and just pour
    Metal is a much better heat conductor than concrete and will additionally strengthen a fairly thin screed


    are you able to determine what mass? In addition, is the installation already fired and how does it work?
    What metal mesh are you thinking of?

    thank you for answering! ;)

    Added after 57 [seconds]:

    ls_77 wrote:
    And how large the surface is to be heated with underfloor?
    What is the room: kitchen, bathroom, hallway or room / living room?
    Is there still other heating, e.g. radiators, or just a floor?


    there are rooms on the first floor, bedrooms, about 80m in total, there are heaters, now we regret that no floor ...: /
  • #9 17050530
    ak44
    Level 27  
    I have read that underfloor heating should not be used in bedrooms. I just can't remember why.
  • #10 17051728
    ls_77
    Level 38  
    ak44 wrote:
    I have read that underfloor heating should not be used in bedrooms

    Yeah. It was also once said that the earth was flat. This is another myth to be refuted :D

    agapyta wrote:
    there are rooms on the first floor, bedrooms, about 80m in total, there are heaters, now we regret that no floor ...: /

    It promises to be quite a big deal. You also need to remember to connect these floor loops somewhere in the manifold, i.e. lead to one common place. So not at all more expensive and maybe cheaper (and certainly better) will be forging entire floors and doing everything according to the art.

    I can't imagine cutting the concrete (even with a grooving tool) that these uncut elements remain intact - they can always crack and fall off. In addition, I would be afraid later that the floor made in such a way will crack and the pipe could be damaged on these cracks.

    And can you afford to raise the entire floor. They are so-called drywall renovation systems, I just can't remember the producers and how much the floor is rising.
  • #11 17052299
    kloszi
    Level 21  
    I furrowed the screed and inserted the pipes into the furrows and later poured a small amount of concrete. The depth varied from 2cm to 5cm (it was spout on the ceiling). Unfortunately, a lot of work with it and you need to have a vacuum cleaner connected to a wall chaser. If you heat with gas all the time, there are no big temperature differences, if you burn it with rubbish for 3-4 hours, you can feel the temperature difference a bit.
  • #12 17052305
    anders11
    Level 30  
    agapyta wrote:
    are you able to determine what mass? In addition, is the installation already fired and how does it work?
    What metal mesh are you thinking of?


    I can't determine the type of mass but I will be on this site in about a month so I can "pull the tongue"
    Metal mesh with mesh around 10mm wire thickness up to 1mm
  • #13 17052515
    agapyta
    Level 2  
    ls_77 wrote:
    ak44 wrote:
    I have read that underfloor heating should not be used in bedrooms

    Yeah. It was also once said that the earth was flat. This is another myth to be refuted :D

    agapyta wrote:
    there are rooms on the first floor, bedrooms, about 80m in total, there are heaters, now we regret that no floor ...: /

    It promises to be quite a big deal. You also need to remember to connect these floor loops somewhere in the manifold, i.e. lead to one common place. So not at all more expensive and maybe cheaper (and certainly better) will be forging entire floors and doing everything according to the art.

    I can't imagine cutting the concrete (even with a grooving tool) that these uncut elements remain intact - they can always crack and fall off. In addition, I would be afraid later that the floor made in such a way will crack and the pipe could be damaged on these cracks.

    And can you afford to raise the entire floor. They are so-called drywall renovation systems, I just can't remember the producers and how much the floor is rising.


    this is the problem I have, what I see is forging or picking up or leaving as it is ... hmmm I thought it would be easier ... thank you for rep!
  • #14 17052613
    vodiczka
    Level 43  
    agapyta wrote:
    there are rooms on the first floor, bedrooms, about 80m in total, there are heaters, now we regret that no floor ...
    I have heaters for 60 years, parquet floor and I do not regret it. If you have such a surface of the radiators that even in freezing days do not have to be very hot to warm the bedroom, then you have similar comfort as with the floor. Since the bedrooms are on the first floor, the floor does not create a sense of cool unless you put ceramic or marble tiles.
    When the radiators are very hot, humidifiers or a wet towel laid on the radiator are necessary.
  • #16 19821164
    Strumien swiadomosci swia
    Level 43  
    The guests who order are just milling concrete with a machine.
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  • #17 19821342
    qwestry1
    Level 9  
    Strumien swiadomosci swia wrote:
    The guests who order are just milling concrete with a machine.


    Well, if you do not have time and resources, you can order it. Here I drop a contact to the company that cut the grooves for my client and is very happy.
    Łukasz Krzyszczuk
    503811849
    https://usuwa-subitu.pl/kontakt/
  • #18 19822050
    Prof. SpecMiernik
    Level 27  
    And how with the spout after such milling? Will not crack? After all, it is spread over polystyrene.
    After all, the milling machine makes grooves to a depth of about 2 cm, i.e. instead of 6 cm of screed / screed, we have 4 cm.
  • #19 19822154
    qwestry1
    Level 9  
    The whole thing is puffed up with high-text glue after inserting the wires - I recommend contact with the Lord whom I have already indicated.
  • #20 19822296
    edziu
    Level 29  
    and if it is on the first floor, there are no balcony windows, then you can put pipes on the existing floor and pour 4-5 cm strong concrete
  • #21 19822367
    William Bonawentura
    Level 34  
    ak44 wrote:
    I have read that underfloor heating should not be used in bedrooms. I just don't remember why.


    Apparently because you cannot leave dirty socks on such a floor - there will be a smell :)
  • #22 19822383
    Mierzejewski46
    Level 37  
    You can mill furrows, you want the warm floor effect because you already have radiators. A furrow 25mm deep and 25mm wide will not weaken the bedding. After positioning the PEX tubes, fill the grooves with Nivoplan Plus Mapei. Make a little none so that the tubes fail well. The furrows may be 15-20 cm apart. No, they have to be every 10 cm. The floor will warm up. The length of the loop is more important. Let them not be longer than 60m.
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Topic summary

✨ The discussion revolves around the feasibility of cutting holes in existing screeds to install underfloor heating pipes. Users share their experiences and concerns regarding the depth of the cuts, which typically range from 2cm to 5cm, and the potential for uneven heating. Suggestions include using a wall chaser for less invasive cutting and ensuring proper insulation beneath the pipes. Some participants recommend electric heating mats as an alternative, while others emphasize the importance of metal mesh for better heat distribution. Concerns about structural integrity and the risk of cracking in the screed are also raised, along with the need for proper installation techniques to avoid future issues. The conversation highlights the importance of loop length and spacing for effective heating.

FAQ

TL;DR: 25 mm-deep x 25 mm-wide milled grooves spaced 15-20 cm apart give “the warm floor effect with no cracking observed” [Elektroda, Mierzejewski46, post #19822383] Most users add a 20 mm topping for strength [Elektroda, anders11, post #17050218]

Why it matters: Milling saves tearing out fresh screed and keeps finished floor heights almost unchanged.

Quick Facts

• Groove depth: 20–25 mm; width: 25 mm [Elektroda, Mierzejewski46, post #19822383] • Pipe spacing: 15–20 cm for bedrooms [Elektroda, Mierzejewski46, post #19822383] • Minimum new top layer: ≈20 mm fibre-reinforced screed [Elektroda, anders11, post #17050218] • Max loop length: ≤60 m to limit pressure drop [Elektroda, Mierzejewski46, post #19822383] • Milling service cost: approx. €20–30 / m² (Germany, 2023) [“Bodenheizung Fräsen Kosten”]

Can I cut grooves in an existing screed for hydronic underfloor heating?

Yes. Users milled 2–5 cm-deep channels with a wall-chaser or concrete milling machine, then laid PEX pipes and re-poured [Elektroda, kloszi, post #17052299]

Will the floor heat evenly after milling?

With 15–20 cm spacing and a 20 mm topping, users report uniform warmth; only rapid, high-temperature firing caused slight variation (~2 °C) [Elektroda, kloszi, post #17052299]

Does milling weaken the screed or cause cracking?

A 25 mm channel in 60 mm screed leaves sufficient structure; topping with high-flex mortar or fibre screed prevents cracks [Elektroda, Mierzejewski46, post #19822383]

How can I improve heat distribution in a thin topping?

Lay metal mesh (≈10 mm grid, 1 mm wire) over pipes before pouring; metal spreads heat and strengthens the layer [Elektroda, anders11, post #17050218]

Is underfloor heating suitable for bedrooms?

Yes. Modern low-temperature floors stay below 27 °C surface temperature, meeting health guidelines and user comfort [CIBSE Guide A, 2020].

What tools and dust control do I need?

Use a twin-blade wall-chaser with a HEPA vacuum attachment; expect significant silica dust without extraction [Elektroda, kloszi, post #17052299]

How do I connect upstairs loops to a manifold?

Run supply/return pairs down a service shaft to a manifold near the boiler; keep each loop ≤60 m to match pump capacity [Elektroda, ls_77, post #17051728]

What is the cost difference versus full floor replacement?

Milling plus refill averages €20–30 / m²; removing and reinstalling screed can exceed €45 / m² excluding disposal [“Bodenheizung Fräsen Kosten”].

Edge case: What if my screed is only 40 mm thick?

Avoid milling; instead use an overlay renovation panel system that adds 18–25 mm height without cutting [Elektroda, ls_77, post #17051728]

Could I use electric heating mats instead?

Mats need only a 5 mm skim coat and one groove for a sensor, but operating costs are 2–3 × higher with gas at €0.08 / kWh [Elektroda, Parowy, post #17050170]

Quick 3-step milling procedure?

  1. Mark 15–20 cm centres on the floor.
  2. Chase 25 mm-deep grooves with dust extraction.
  3. Lay PEX, pressure-test, then fill grooves with polymer screed and 20 mm top coat.
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