UFH spec for use with heat pump
Discussion
Hi,
we're getting a underfloor system installed in an old victorian property. Raised timber floors so the pipes go in between joists in a small screed on top of kingspan.
We don't have a heat pump and won't be able to afford it for a year or so but want to leave the UFH so it will work reasonably if we get one (give we have all floors up anyway). It will be an air sourced one. For the time being we'll use oil fired boiler and this will stay in place to "top-up" the ASHP when its installed. I'm not expecting the ASHP to provide all heating (we're in Scotland and it was down to -15 last winter) so there will be some kind of blending and the boiler will kick in as needed.
The installer has suggested a 40mm screed (biscuit mix) on top of 80mm kingspan. Pipes are to go in at 200mm spacing. I'm a bit worried about the pipe spacing from what I've read - should maybe be 100-150mm?
The screed can't be much deeper than 40mm because of joist depth and also would like to keep weight down.
Floor finish will be 22m engineered oak boards (which are structural so go right on joists).
Know some people on here have experience of heat pumps and would really appreciate any comments.
thanks.
we're getting a underfloor system installed in an old victorian property. Raised timber floors so the pipes go in between joists in a small screed on top of kingspan.
We don't have a heat pump and won't be able to afford it for a year or so but want to leave the UFH so it will work reasonably if we get one (give we have all floors up anyway). It will be an air sourced one. For the time being we'll use oil fired boiler and this will stay in place to "top-up" the ASHP when its installed. I'm not expecting the ASHP to provide all heating (we're in Scotland and it was down to -15 last winter) so there will be some kind of blending and the boiler will kick in as needed.
The installer has suggested a 40mm screed (biscuit mix) on top of 80mm kingspan. Pipes are to go in at 200mm spacing. I'm a bit worried about the pipe spacing from what I've read - should maybe be 100-150mm?
The screed can't be much deeper than 40mm because of joist depth and also would like to keep weight down.
Floor finish will be 22m engineered oak boards (which are structural so go right on joists).
Know some people on here have experience of heat pumps and would really appreciate any comments.
thanks.
thanks, tile not really an option. The engineered wood with no ply or chipboard underneath seemed next best option. We have 400mm between joists (approx) so I can't see problem with 100mm spacing (and the extra pipe cost seems negligible in grand scheme).
I don't have huge expectations for the ASHP (assume the boiler will still be raising tempertature up and upstairs still has radiators) - just want to get UFH in first.
I don't have huge expectations for the ASHP (assume the boiler will still be raising tempertature up and upstairs still has radiators) - just want to get UFH in first.
orbit123 said:
I don't have huge expectations for the ASHP (assume the boiler will still be raising tempertature up and upstairs still has radiators) - just want to get UFH in first.
Where about are you?Air source will have no probs with under floor for at least 90+ % of the year, and should do radiators for at least 75% of the time. You are using suitable radiators for ASHP and are aware they will be cooler than conventional rads.
If running on rads and UF you will either need a cold mix to lower the floor temp, run the rads cool or run the floor too hot.
Normal UF temps are max about 45 C.
If I get a chance tomorrow pm I'll try and get some ratings for you for a ASHP and UF pipe spacings.
many thanks for any advice you can give. I've oversized the radiators by a percentage.
The plumber has spec'd different valves for mixing each floor to correct temperature and I'm getting quite a good control system (heatmiser). My thought is that with the spacing at 200mm, being an older property, wood floors etc that a tighter spacing must give out more heat if its all running at a lower temperature. i.e. if we put in a greater area of pipe then we'll need less heat from the boiler overall and we'd get better value from the ASHP.
If we never install the ASHP then I've put in more pipe and effort than was needed but the system will still work absolutely fine with the tighter pipe spacings (just runs at a lower temperature of water).
I'm near Glasgow in Scotland - did have temps down to -15 last winter but its very rare they get that low.
You think 40mm screed is ok (its suspended timber floor)?
The plumber has spec'd different valves for mixing each floor to correct temperature and I'm getting quite a good control system (heatmiser). My thought is that with the spacing at 200mm, being an older property, wood floors etc that a tighter spacing must give out more heat if its all running at a lower temperature. i.e. if we put in a greater area of pipe then we'll need less heat from the boiler overall and we'd get better value from the ASHP.
If we never install the ASHP then I've put in more pipe and effort than was needed but the system will still work absolutely fine with the tighter pipe spacings (just runs at a lower temperature of water).
I'm near Glasgow in Scotland - did have temps down to -15 last winter but its very rare they get that low.
You think 40mm screed is ok (its suspended timber floor)?
The usual advantage with underfloor is the energy storage in the concrete, sounds like you may miss out on this to some extent.
Therefore fit pipes at more like 150 centres, the extra cost is very small.
I would recommend radiators twice the normal size.
Running a heat pump is different to other heating sources - do NOT take water up to high temperatures and temper it back down - it ruins efficiency.
You can have oil and a heat pump in parallel, (I've done a couple of houses like this), you must ensure the heat pump has a powerful circulating pump - (a standard 99w one is not big enough) and you may need some one way valves make sure the water circulates the right way.
thanks. Radiators are not quite twice normal size (they're getting to a crazy size in terms of wall space) but are oversized and proper cast iron. I'm hoping the cast will be a bit of a heat retainer.
I expect that the depth of screed will matter quite a bit in retaining some of the heat but its limited by depth of the joists and the weight.
I expect that the depth of screed will matter quite a bit in retaining some of the heat but its limited by depth of the joists and the weight.
The RHI Premium Payment is available from june this year - basically an upfront fee to stave off the rioting eco middle classes until the RHI proper kicks in autumn 2012. They are having a big push for those off-grid like yourself - oil / LPG users, but the implication currently is that to qualify you would have to replace an existing boiler entirely, not have a bivalent system. Secondly, the RHI as ity currently stands (assuming they don't tweak it between now and next year) is calculated on the heat demands of the house - so even if they did allow the bivalent system, if you have a certain percentage of that demand met by oil, then you'd only get RHI on the remaining amount... so it could drastically alter your return.
Also, they're not happy with ASHP in general either, hence why it's not included in the Commercial RHI right now, so it's more than likely they could yet exclude it entirely from domestic RHI too, in which case the above issues are somewhat moot!
Also, they're not happy with ASHP in general either, hence why it's not included in the Commercial RHI right now, so it's more than likely they could yet exclude it entirely from domestic RHI too, in which case the above issues are somewhat moot!
ah yes, thats the £850 one off if its an ASHP. I think we'd need to get a new energy certificate done and even then the house is old and might not qualify. The longer term RHI is of interest though.
We have 3 phase power which electrician thought might help with getting a large enough heat pump - or even 2 of them if needed.
Would need to keep the oil boiler as a backup though.
We have 3 phase power which electrician thought might help with getting a large enough heat pump - or even 2 of them if needed.
Would need to keep the oil boiler as a backup though.
Well then it's the bivalent install you'd need to thoroughly check out - we looked at leaving ours in and were told very firmly by three different suppliers that it'd negate any claim on the RHI as it currently stands.
Lucky you with 3-phase - we've just had a quote to upgrade our incomer from single to 3, and despite being 20 yards from the transformer, and the only property on that transformer, they somehow managed to conjour up a quote for £26k! Madness.
Lucky you with 3-phase - we've just had a quote to upgrade our incomer from single to 3, and despite being 20 yards from the transformer, and the only property on that transformer, they somehow managed to conjour up a quote for £26k! Madness.
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