Air source heat pump flow temperature and underfloor heating.

[Joshua Graham]

Hi, I am currently renovating a 60s property as my first home. I am getting an air source heat pump installed, as oil is no longer a financially viable option. I want to run my heat pump at 35 to heat the house using underfloor heating on the ground floor. The ground floor is suspended timber floor, with new sheets of chipboard down. I have been looking into systems that you can lay atop the existing floor and was looking for advice as to what type of pipe centers for this as some places have said 100mm but there are no products out there that do pipe centers this close! I think its worth noting I have underfloor insulation of 60mm of pir and 150mm of mineral wool, and a membrane to protect against drafts, 600mm mineral wool in eves and bead cavity filling. I have also filled any openings i could find, to prevent air leaks. Are 100mm center overkill? Would 35 degrees work at 150mm centers or even 200mm? If not, could I cnc the center my self into my existing chipboard floor or a layer on top of the existing chipboard then lay 6mm of ply?

 

Thanks

 

JG

[ReedRichards]

3 hours ago, Joshua Graham said:

Would 35 degrees work at 150mm centers or even 200mm? 

 

 

The lower the water flow temperature and the larger your pipe spacing then the lower will be your heat output per square meter of floor.  What will work depends on what you need.  By chance, earlier today I came across this table: https://www.tradingdepot.co.uk/info/plumbing/polypipe/underfloor-heating-heat-output-tables/  It doesn't help directly because it does not go down below 40 C flow but it gives an idea of the dependencies. 

[Olf]

8 hours ago, Joshua Graham said:

600mm mineral wool in eves and bead cavity filling

It sounds like you have good level of insulation now, but you still need to do your maths homework to know how much heat input you need to balance all the losses  - see 

 

 

Once you know the heating power needed divide over floor area to get required output per area and that will tell you if 35'C is realistic

 

8 hours ago, Joshua Graham said:

some places have said 100mm but there are no products out there that do pipe centers this close!

Using clips you can do whatever you want  I'm not sure though if there are any on the market that are designed for hard surface.

100mm centres should increase your heat output, but there is more to the story (shape of the loop, length) that may affect it and make no better than 150mm centres

 

 

8 hours ago, Joshua Graham said:

could I cnc the center my self into my existing chipboard floor or a layer on top of the existing chipboard then lay 6mm of ply

No cnc, because after routing 16mm channels for pipes your floor will become as stable as cheese. 

If you find a way to attach pipes to the boards you could pour thin fiber reinforced screed  - look at Lewis deck for inspiration

[Joshua Graham]

4 hours ago, Olf said:

It sounds like you have good level of insulation now, but you still need to do your maths homework to know how much heat input you need to balance all the losses  - see 

 

 

Once you know the heating power needed divide over floor area to get required output per area and that will tell you if 35'C is realistic

 

Using clips you can do whatever you want  I'm not sure though if there are any on the market that are designed for hard surface.

100mm centres should increase your heat output, but there is more to the story (shape of the loop, length) that may affect it and make no better than 150mm centres

 

 

No cnc, because after routing 16mm channels for pipes your floor will become as stable as cheese. 

If you find a way to attach pipes to the boards you could pour thin fiber reinforced screed  - look at Lewis deck for inspiration

Thanks for the help, that spreadsheet will come in super handy! Ye the CNC part I was meaning lay 22mm ply atop the existing new 22mm chipboard, this way I can make custom shapes for the loops. The reason I opted out of screed is my floor is suspended and the joists might not take the extra weight or could sag in places, and move which would crack the screed. What are your thoughts?

[Olf]

9 hours ago, Joshua Graham said:

The reason I opted out of screed is my floor is suspended and the joists might not take the extra weight or could sag in places, and move which would crack the screed

I've just finished laying this system: EPS panels with 5-8mm Mapei 3240 screed on top.

It adds only about 20kg/sqm, so well within bearing capacity of any existing floor. Frankly, thanks to load now spreading via new P5 boards, the point load is actually reduced (vs original floor boards, working pretty much independently as indicated by creaking - one of the reasons I decided to lift them), so there is less sagging and bouncing.

 

EPS panels are very easy to route (if messy), though of course it would be much easier to use pre-made channels at 150mm centres, especially if serpentine is the layout of your choice. Also when extra grooves are added, more screed flows into them (or rather those you don't use) so you'd end up using more screed, making the floor a bit heavier (but sturdier at the same time) - I ended using 25kg bag per 1.5 sqm for 6mm, on a flat surface that should cover twice the area, so much goes into unused channels.

 

I can't yet say about performance, I'm few days away from connecting to the existing system.

[HughF]

23 hours ago, Joshua Graham said:

Hi, I am currently renovating a 60s property as my first home. I am getting an air source heat pump installed, as oil is no longer a financially viable option. I want to run my heat pump at 35 to heat the house using underfloor heating on the ground floor. The ground floor is suspended timber floor, with new sheets of chipboard down. I have been looking into systems that you can lay atop the existing floor and was looking for advice as to what type of pipe centers for this as some places have said 100mm but there are no products out there that do pipe centers this close! I think its worth noting I have underfloor insulation of 60mm of pir and 150mm of mineral wool, and a membrane to protect against drafts, 600mm mineral wool in eves and bead cavity filling. I have also filled any openings i could find, to prevent air leaks. Are 100mm center overkill? Would 35 degrees work at 150mm centers or even 200mm? If not, could I cnc the center my self into my existing chipboard floor or a layer on top of the existing chipboard then lay 6mm of ply?

 

Thanks

 

JG

My thoughts? An oil combi is probably the cheapest way of delivering heat and dhw at current energy prices…. 
 

if you do want to go down the ashp route, it’s all about the floor buildup. Do you have the height to play with? For example in my place, I don’t so I’m looking at the omni torfloor2 system.

[ReedRichards]

I got a heat pump in December 2020 at which time I was paying 13p per kWh for my electricity, now I pay 33.76 p per kWh (figures include VAT, exclude Government rebate).  The average price I had paid for my heating oil in the two years or so prior to 2021 was 45.19 p per litre (average not weighted for quantity).  Now heating oil is somewhere close to £1 per litre, I understand.  So the balance has certainly swung in favour of heating oil since my heat pump was installed; oil has gone up in price by a lesser percentage than the cost of the cheapest electricity deal available.     

[Joshua Graham]

4 hours ago, HughF said:

My thoughts? An oil combi is probably the cheapest way of delivering heat and dhw at current energy prices…. 
 

if you do want to go down the ashp route, it’s all about the floor buildup. Do you have the height to play with? For example in my place, I don’t so I’m looking at the omni torfloor2 system.

I can build up if need be, yes, what is the suggestion?

[HughF]

19 minutes ago, Joshua Graham said:

I can build up if need be, yes, what is the suggestion?

Egg crates, 16mm pipe, many many many bags of ultraplan renovation

 

Jokes aside, you've got loads of options if you aren't build-up height limited.

Edited October 4, 2022 by HughF

[Joshua Graham]

1 hour ago, HughF said:

Egg crates, 16mm pipe, many many many bags of ultraplan renovation

 

Jokes aside, you've got loads of options if you aren't build-up height limited.

I do like the idea of screed as is it retains gets a slower more even release of heat my only worry is if it cracks due to floor movement... the joists have a bit of movement on them, would that be an issue?

Edited October 4, 2022 by Joshua Graham

[HughF]

17 minutes ago, Joshua Graham said:

I do like the idea of screed as is it retains gets a slower more even release of heat my only worry is if it cracks due to floor movement... the joists have a bit of movement on them, would that be an issue?

What matters is what you're putting on top.... ceramic tile, that won't be happy with a moving floor.... Carpet or vinyl, that won't care.

[Joshua Graham]

2 minutes ago, HughF said:

What matters is what you're putting on top.... ceramic tile, that won't be happy with a moving floor.... Carpet or vinyl, that won't care.

Engineered wood. so less movement allowed than carpet but a touch more than tiles i guess tho. With the egg crates would i need to put a vapour barrier under? I already have one under the existing chipboard see to stop cold air traveling up gaps. I think this could cause a breathability issue. 

[Glenn]

Continal will do 100mm spacing, but I think with on!y 12mm pipe. Which could be similar output as 16mm on 150mm spacing

 

Regards

Glenn