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Expanding the system

 
Air Source Heat Pumps (ASHPs)
Last Post by Judith 3 months ago
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 KundK
(@kundk)
Trusted Member Member
Joined: 4 years ago
Posts: 19
Topic starter 08/02/2025 4:12 pm  

Hi,

 

We have an 8kW Samsung ASHP heating the 3 bed house (cca 80sqm) through 7 radiators and a towel rack. It's working fine although in colder weather it's working hard to keep 21C all around the house.

 

We're planning a full bathroom renovation which includes breaking up and pouring new concrete floor. I'd really like to put underfloor heating in there at the same time (now or never). It's a small bathroom, less than 5sqm. 

But I have a little worry about overloading the heat pump.

 

Could you give me advice in the question? Unfortunately the installer went out of business, so I can't ask them.


   
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 JohnR
(@johnr)
Estimable Member Member
Joined: 6 months ago
Posts: 106
09/02/2025 7:33 pm  

There should be no significant change in the load on the heat pump unless you keep the bathroom hotter and thus increase the losses through walls and ceiling. However, there may be a need for some associated modifications to the heating system.


   
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 KundK
(@kundk)
Trusted Member Member
Joined: 4 years ago
Posts: 19
Topic starter 10/02/2025 10:20 am  

Posted by: @johnr
↑

There should be no significant change in the load on the heat pump unless you keep the bathroom hotter and thus increase the losses through walls and ceiling. However, there may be a need for some associated modifications to the heating system.

 

I'm sure the bathroom will be warmer. Which would be one of the purpose of this. But since it's quite small, I think the additional heat loss would be small too.

 

What additional modification would you expect?

 


   
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 Judith
(@judith)
Prominent Member Member
Joined: 1 year ago
Posts: 344
10/02/2025 2:54 pm  

@kundk you haven’t said where your bathroom is. If it’s on the ground floor and the floor is concrete is it insulated underneath. The age of your house will determine that.

Be careful with suppliers since some will try and push you to an electric heated floor which will be MUCH more expensive to run, but probably cheaper and easier to install.

Despite saying they are suitable for ufh some materials can only be heated to less that 29C (like our vinyl tiles) so you have consider everything together. You will need a space for the ufh manifold and down mixer for the water flow if you do want a surface like this. Ceramic tiles are best and remove that limitation, but there are guidelines on maximum floor temperature since feet can be burned, especially childrens’.

We love our ufh because it’s so gentle and comfortable with no radiators taking up space and wish it had been feasible to have it all round but solid concrete floors in our case made it unviable. 

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with it) open system operating on WC


   
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 KundK
(@kundk)
Trusted Member Member
Joined: 4 years ago
Posts: 19
Topic starter 10/02/2025 5:34 pm  

@judith 

OK, so it's a bungalow built in 1969. As far as I know the concrete is only "insulated" with thin asbestos tiles at the top. But it is sinking (not the walls, only the concrete slab), so I want to break it up and re-pour anyway.

While doing that, we'll put 70-100mm insulation below it. And then could come the UFH, screed and tiles.

We want ceramic tiles anyway, so it won't be an issue. Mixer might needed. The max water temperature is 50C if I recall correctly.

 

I had a house with UFH, no need to convince me. 🙂

And they can try to push me to electric, but that won't happen.


   
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 Judith
(@judith)
Prominent Member Member
Joined: 1 year ago
Posts: 344
10/02/2025 6:01 pm  

@kundk you probably already know the builder/plumber will have to get a specialist in to remove the tiles because of the asbestos.

It is worth having the space between your underfloor pipes to be 100mm, since it gives you more heating options. Many plumbers will tell you that you won’t need that with insulation under your newly poured slab. With that extra heat you might not need a heated towel rail to supplement the room.

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with it) open system operating on WC


   
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