First bit of advice needed...

[CotswoldDoItUpper]

Hi All, 

 

Jumping in here needing to ask about UFH.

 

We will be (long term) installing an ASHP to run UFH but we cant afford that yet so in order to make the house reasonably decent to live in were renovating and therefore starting by installing the flooring inc UFH. It will be powered by willis heaters (thanks to BH for that suggestion!) in the meantime.

 

We suspended timber floors on the GF and therefore as I see it have 2 options (please correct me if I'm wrong or there is a better way!).

 

Option 1:

a- remove existing floor coverings and floorboards

b- install 100mm PIR in between the joists, expander foam gaps and tape

c- 18mm ply over

d- lay pipe insulation boards and install pipes

e- tile directly the boards (no screed) with flexible adhesive and grout. We will be using natural stone so may need a decoupling membrane. Any advice?

 

Option2:

a- remove existing floor coverings and floorboards

b- install netting between joists and fill with rock wool or similar

c- lay pipes in spreader plates (prob ok in  the 1980s part, what happens in the 1800s part when the joists won't be regular?)

c- 18mm ply over

d- tile over with flexible adhesive and grout. 

 

Other questions:

- We will be doing zones 1, 2 and 3 first. Is zone 2 too big be one circuit? the room is approx 5 x 8m (typo on the plans - 41sqm not 31) giving a pipe run of about 200m. Think I'll have to split this into 2a and 2b

- Is there an issue with having accessible joints in the UFH loops? We need to run the pipes from the manifold an area (prob in the corner of zone 5) ready to do the lower levels when funds allow before finishing the floor in zone 3. The unused pipes will then be capped ready to take the extra loops when ready. 

- There is a 750mm difference between zone 3 and zone 4, with zone 4 etc being lower. Do I need a second manifold/pump etc for the lower level or can it be run off the same unit?

- Is there any benefit to either option above? I can see pros and cons of each but no definite winner. Head-height is lower then standard (2.3m) in the 'new' bit and 1.9-2.2 in the 'old' bit, depending where you stand. Think it might be option 1 in the new bit and option 2 in the old bit due to spreader plates not fitting, but I don't like the idea of having a big chunk of ply wood soaking up all the heat from the pipes if they're between the joists.

 

Thanks for taking the time to read though this, any advice/guidance/abuse welcome!

 

CDIU

 

 

[MikeSharp01]

3 hours ago, CotswoldDoItUpper said:

Is zone 2 too big be one circuit?

No (Even at 41 m²)

 

3 hours ago, CotswoldDoItUpper said:

- Is there an issue with having accessible joints in the UFH loops? We need to run the pipes from the manifold an area (prob in the corner of zone 5) ready to do the lower levels when funds allow before finishing the floor in zone 3. The unused pipes will then be capped ready to take the extra loops when ready. 

Do each loop as one continuous run but if you must have connectors then definitely make them accessible.

 

3 hours ago, CotswoldDoItUpper said:

- There is a 750mm difference between zone 3 and zone 4, with zone 4 etc being lower. Do I need a second manifold/pump etc for the lower level or can it be run off the same unit?

As there will be a height and therefore pressure difference it might be worth having an extra pump for the upper circuit but it may be possible to balance it using the manifold flow adjusters. Depends on height difference, pump pressure / flow and adjustment range.  A big pump should do it but might be noisy! You can get some pumps with two separate impellers which might be a way forward.

 

3 hours ago, CotswoldDoItUpper said:

ply wood soaking up all the heat from the pipes if they're between the joists.

This is not a big problem as it will transfer the heat up and out into the room anyway. 

 

Sounds like head height will be your controlling factor on the options but don't forget that getting the pipes down low may well mean channeling the joists to get the pipes between compartments. However for the old part this feels like the best option to me but I am 6'4"!.

What is below the bottom of the joists - a gap, the soil immediately or what?

 

Others will be better able to help on the tiling to boards.

[CotswoldDoItUpper]

Thanks @MikeSharp01 we have decided on going for spreader plates all over to keep room heights as much as possible. Zone 2 is going to be about 250m pipe, so it’s going to have to be a big pump to cope with that! What counts as a ‘big’ pump? How are they measured? Guess it’s not just size! 
Most sites say max run of 100m but I thought that that might be marketing to get you to buy an extra manifold or other accessories. If 250m is ok then we’ll go for that!!
We have an air gap and soil/rubble under joists - hence the need for insulation. 
We will have to have joints unfortunately due to the phasing of the project so will make sure these joints are easily accessible in case of emergencies!!

[PeterW]

15 minutes ago, CotswoldDoItUpper said:

Most sites say max run of 100m but I thought that that might be marketing to get you to buy an extra manifold or other accessories. If 250m is ok then we’ll go for that!!

It isn’t and it will cause cold spots. Run it as three loops of 80m, it will be an extra £20 on the manifold cost. 

 

On 28/06/2021 at 12:27, MikeSharp01 said:

No (Even at 41 m²)

Yes it is too big to be one circuit but not one zone. See above. 

[PeterW]

On 28/06/2021 at 08:50, CotswoldDoItUpper said:

We will be (long term) installing an ASHP to run UFH but we cant afford that yet so in order to make the house reasonably decent to live in were renovating and therefore starting by installing the flooring inc UFH. It will be powered by willis heaters (thanks to BH for that suggestion!) in the meantime.

What is there now ..? A 3kW Willis won’t replace a 25kW boiler so if you’re doing this in stages why not just hook the UFH to the existing heat source via a buffer if needed ..?

[CotswoldDoItUpper]

41 minutes ago, PeterW said:

What is there now ..? A 3kW Willis won’t replace a 25kW boiler so if you’re doing this in stages why not just hook the UFH to the existing heat source via a buffer if needed ..?

I was thinking of having 2 in parallel as a back up for the ASHP anyway long term so that was the only logic. Other then that it’s only half the house and no HW so assuming we had a 16kw ASHP and therefore only using 1/2 (half the house) that’d be 8kw so 6kw not far off. Have I got this wrong? Happy to be corrected! Have no idea how to spec/cost up hooking to existing lpg combi with a buffer! Every day is a school day!

[PeterW]

So a buffer isn’t that difficult - you just add it into the heating circuit. It is just a tank in the system that the heating runs into one pair of tappings and the UFH runs off another pair. When you swap to an ASHP then you just add it to a third set of tappings. 
 

Adding an immersion to this isn’t a problem if you want backup. 
 

How are you planning on doing DHW ..?

[CotswoldDoItUpper]

1 hour ago, PeterW said:

So a buffer isn’t that difficult - you just add it into the heating circuit. It is just a tank in the system that the heating runs into one pair of tappings and the UFH runs off another pair. When you swap to an ASHP then you just add it to a third set of tappings. 
 

Adding an immersion to this isn’t a problem if you want backup. 
 

How are you planning on doing DHW ..?

 
thanks, think that makes sense! Or I’ll get a plumber to do it. DHW is currently ask LPG combi but will switch to a cylinder when switching to ASHP. Think this all makes sense in my head anyway!! Such a brain fog trying to work it all out.

[CotswoldDoItUpper]

@PeterW on that note, how big should a buffer tank be? #CluelessNewbie

[PeterW]

Start with 100 litres which should be fine. 

[CotswoldDoItUpper]

@PeterW guess I’ll also need an expansion tank for that too? What size do you think? This is getting more and more complicated (and expensive!) by the day!

[PeterW]

1 hour ago, CotswoldDoItUpper said:

@PeterW guess I’ll also need an expansion tank for that too? What size do you think? This is getting more and more complicated (and expensive!) by the day!

UFH isn’t cheap to install so it’s just part of the costs. The system should already have an expansion vessel somewhere already ..?

[CotswoldDoItUpper]

We’re starting by just laying the insulation, sub floor pipes and membrane/tiles. Will actually commission it when we can add bits.

 

if we lay PIR between joists, 18mm chipboard over then lay the 20mm routed insulated boards for pipes over the top will that be enough to avoid cold bridging through the joists? Think this is the way we’re going to go if it does.

 

tia!