Any good sources for cost/practicalities/etc comparisons of UFH vs rads for low-temp heat pump driven system?

[YodhrinForge]

As title, unfortunately these days search engines just spit out 500 basically identical AI-slop "summaries" of the blatantly obvious occasionally interspersed with completely objective and unbiased examinations of the facts that always seem to think the best option is whatever one the company who made the website can sell you. I'm trying to choose between insulating suspended timber floors with membranes & wood fibre(and figuring out some way to vent the cavity as it currently isn't and the walls are half a metre of stone) with replacement low temp rads, or ripping them out and doing UFH in insulated concrete slabs, but trying to piece together a proper understanding of the costs and details is a pain in the backside(This website says That much, but is That just for the UFH tubes and a couple of lads to put them in or does it include insulation, concrete pours etc? Who knows). If there was a site that broke down in general terms pro vs DIY costings for both options that would be a godsend.

[JohnMo]

Break it down to clear decisions 

 

Radiators yes or no. You need to do room, by room heat loss calculation, choose a max flow temp, then decide can I live with size radiator? Assuming not move to UFH 

 

UFH you need insulation under it. Ideally the equivalent of 150mm PIR, to enable low flow temp. Can you do that with the existing floor make up? If not dig out and down. Will not be cheap and you will have to pull house apart.

 

Third option could be way easier and cheaper. Insulate to best best bang for the buck, look for air leaks and fix - all pretty cheap. Address how the building is ventilated, which is missed by most.

 

Either fan coils with A2W HP, or A2A heat pump. Both options allow small heat emitters, A2W would be sized to use a max of 35 degs. A2A would be better a working solution out the box, one outside unit and multiple indoor emitters.

[joth]

Costs depend vastly on what your starting point is, which is not very clear. 

Do you already have a completely finished occupied house you're planning a heating retrofit to, or just some plans being prepared for planning permission, or something in-between? 

[YodhrinForge]

1 hour ago, joth said:

Costs depend vastly on what your starting point is, which is not very clear. 

Do you already have a completely finished occupied house you're planning a heating retrofit to, or just some plans being prepared for planning permission, or something in-between? 

I'm moving into a house that is in habitable condition but has minimal if any energy efficiency measures(stone built late 1800's cottage with somepoint-in-latter-part-of-20th-century block extension & attic conversion, approx 65sqmof ground floor  is suspended timber) presently on a gas boiler with radiators. My intention is to get as close to EnerPHit as I can without spending a fortune, and I'm trying to figure out which strategies to pursue for individual elements(floors, walls, roof, heating, battery etc etc). I intend to handle as much of the renovation as I can myself, I've been researching stuff for a solid year so I know pretty much what's involved in the process of *doing* any given element, but finding even vague information on *roughly* how much one option vs another will cost is proving a pain in the backside - for example, I can roughly cost out the "insulate existing suspended timber" option as I can know exactly what materials I need to order in approximately what quantities and I'd do the labour myself, but finding information on professional costs for the job is like pulling teeth. Some sites will give you a ballpark figure(and I only need a ballpark figure, I know you need specific info about a job to give a proper quote, but if someone asks me to build them a PC I only need a general idea of their use case to give them a rough idea what sort of money it's going to cost them and getting that kind of request is completely normal in almost every "doing things for money" field I've been in or interacted with *except* building trades who seem to delight is keeping as much information to themselves as they can), but for what? "A UFH system", but is that just the pipework and labour to install that? Does it include insulation? Does it include the cost of ripping out existing flooring?

 

I just need enough information about cost to meaningfully compare the options available, and if I went down the UFH route to decide whether it's worth buying the tools and investing the time to do it myself or to hire pros etc(I'll be working on the project full time so the usual price of my time/pay a pro calculus is a bit different to someone who'd be slogging away evenings and weekends after their regular job).

Edited January 27 by YodhrinForge

[sharpener]

Have you condidered paying a Quantity Surveyor to give you some comparative figures? They have access to a regularly updated database of common construction elements.

 

FWIW I have a house with similar wall construction and the radiator sizes for 47.5C av temperature are manageable.

 

If you have an existing suspended timber floor without any ventilation of the cavity below have you lifted some boards to see if the joists are in good condition? IME in a (different) terraced Victorian cottage, even with airbricks front and back there was quite a lot of damp and consequent rot particularly near the party walls.

[joth]

2 hours ago, YodhrinForge said:

My intention is to get as close to EnerPHit as I can without spending a fortune

In this case forget about the heating system. Start by working out how you are going to get 160mm+ of insulation under the floor, remove or minimise thermal bridge through all the existing supporting walls+foundations, and seal junctions to make it all airtight.

That's going to be the expensive/labour intensive part of the job. Once done you have various options on UFH you can price up but they'll be a fraction of the above works.

(On our Enerphit, we had to dig out an existing 60s concrete slab and excavate down 500mm to completely relay the floor slab - one of the more expensive steps but once we decided this all the other decisions pretty much fell into place around it)

 

 

2 hours ago, sharpener said:

Have you condidered paying a Quantity Surveyor to give you some comparative figures?

A QS won't design it for you though - you need to give them some detailed plans of what floor/wall/roof build ups you're going to use.

 

I'd start with a PH designer or PH architect. even if you're not going for a certified retrofit, they'll be best placed to give you the options in your budget.

 

Edited January 27 by joth

[IGP]

I’d love to have gone Enerphit just for the warm fuzzy feeling of being in a highly insulated house. However, I just couldn’t make the sums work, and ended up focusing on airtightness, loft insulation, CWI, suspended floor insulation, MVHR. No major insulation work like IWI / EWI though. It’s a 1930’s semi detached. 
 

Then, I’ve done my heat loss, upgraded all the rads to run at 38c flow at -3c OAT and getting my energy use down further through high SCOP of my heat pump I’ll be installing later this year. So, I’ll be going from 18,000kWh+ gas/year pre-renovation to 10,000kWh now and then to around 2500kWh electricity (assuming all goes well with the HP as planned) for heating and DHW. 
 

But horses for courses and people do it differently 🙂

[YodhrinForge]

On 27/01/2025 at 14:09, sharpener said:

Have you condidered paying a Quantity Surveyor to give you some comparative figures? They have access to a regularly updated database of common construction elements.

 

FWIW I have a house with similar wall construction and the radiator sizes for 47.5C av temperature are manageable.

 

If you have an existing suspended timber floor without any ventilation of the cavity below have you lifted some boards to see if the joists are in good condition? IME in a (different) terraced Victorian cottage, even with airbricks front and back there was quite a lot of damp and consequent rot particularly near the party walls.

Dealing with the cavity is one of the things I've gotten useful into about here previously, and also one of the reasons doing insulated slabs instead is appealing if I could cost them out right. As far as I can tell my best option would be to duct in fresh air to two or three points around the perimeter and then run an extract duct up the disused chimney and whack an anti-backdraft cap on there and rely on passive stack effect/wind draw to pull fresh air in through the supply ducts. The exterior walls are almost half a metre thick so I'm not going to get any air bricks down there except in the internal partitions. I've not checked the condition myself yet because given the amount of work and that I'll have at least some pro trades on site I need to have the full "destructive" survey done for asbestos, so they'll be putting holes in the walls and floors I can use to inspect afterwards.

 

On 27/01/2025 at 16:38, joth said:

In this case forget about the heating system. Start by working out how you are going to get 160mm+ of insulation under the floor, remove or minimise thermal bridge through all the existing supporting walls+foundations, and seal junctions to make it all airtight.

That's going to be the expensive/labour intensive part of the job. Once done you have various options on UFH you can price up but they'll be a fraction of the above works.

(On our Enerphit, we had to dig out an existing 60s concrete slab and excavate down 500mm to completely relay the floor slab - one of the more expensive steps but once we decided this all the other decisions pretty much fell into place around it)

 

 

A QS won't design it for you though - you need to give them some detailed plans of what floor/wall/roof build ups you're going to use.

 

I'd start with a PH designer or PH architect. even if you're not going for a certified retrofit, they'll be best placed to give you the options in your budget.

 

Yeah I'd hoped to have more of a plan in place before I went to an architect but I suspect you're right. The heating system is just one factor in deciding which approach to take with the floors. I'm pretty set on the insulation/airtight methodology already based on my research; take it all back to bare stone, venetian lime-clay plaster as a parge & levelling coat, rigid wood fibre boards bonded to the wall with same, then a stud wall hard up against the rigid boards(services and easier finishing) with the floppy wood fibre batts stuffed in for exterior walls and the densest acoustic rockwool for the border with next door, then clayboard with more venetian plaster to finish. Fully vapour open and the plaster is both alkaline from the lime and great at wicking any moisture that does end up in the walls out thanks to the clay. House will have MVHR obviously so I'm not too worried about needing a vapour membrane but both that and the final thickness of the insulation will have to wait for detailed thermal and humidity modelling. I'll have to use membranes or green-coated OSB for the attic conversion upgrade anyway as the traditional slate construction and being in a conservation area means room-in-roof is required so that just has to be properly detailed at junctions with the downstairs walls, and I'm tempted to get some diathonite to pack in around any embedded joists before I use liquid airtightness goop to seal the joints. With the floor airtightness would either be a dedicated membrane if it remains suspended, or the DPM taped off to the parge layer of the walls if I go with solid floors.