We are doing a complete retrofit of a 150 year old Victorian Vicarage. All the quotes from heat pump suppliers for underfloor heating recommend the installing of overlay panels such as Amideck ontop of the joists. We want to put the original floorboards back ontop of the panels, but I am worried that (a) they will warp/creak/groan, (b) that their thermal resistance will be too high.
Does anyone have experience doing this? Does it work? If so what do we need to look out for?
Many thanks
Mark
Hi Mark, I have no experience on replacing original floorboards on top of UFH panels. My experience is solid floor UFH. However, you may find helpful information within the CIBSE book āThe underfloor heating design & installation guideā. It considers timber floor systems and may match your configuration. The guide adds a caution note against modern timber floors" it is usual for timber floor suppliers to require a maximum limit floor surface temperature of 27C for their products". I think this is due to warping, distortion, concerns. The temperature ceiling has an influence on the overall UFH system design and the maximum mean water temperature possible. The wooden floor ( say 18mm thick) will also add to the thermal resistance of the floor. You are correct in suspecting it probably needs a higher MWT compared with a ceramic tiled floor to achieve the same temperature ( and be less efficient for an ASHP). The re-use of an existing Victorian era wooden floor may create a headache for the installer, since it seems like an unknown quantity. Hopefully others within the community can offer some practical insights. Best wishes on the renovation project.
Is it worth trying the Church authorities? They may well have acquired some experience by now about putting heat pumps into their estate. What leads me to write this is former IEE Committee colleagueās wife was in the clergy, and I remember him saying that the Church was pretty good at keeping their expenses to a minimum, so I think they might be worth approaching.
I am not a expert in underfloor heating but I do own a similar age Victorian detached house with a ground floor made up of wooden floorboards on top of wooden joists.
What I have read/seen suggests underfloor heating is most common with a concrete floor slab directly on the ground, the pipework run across the top of the concrete slab and then a skim on top of that. This allows the entire concrete mass to act as a heat soak and to evenly distribute the heat.
I have however seen a very few examples of underfloor heating pipework being clipped to the bottom of boards running across the top of joists and various material choices on top of those boards. It may have been the US TV show āThis old Houseā which showed renovating āoldā US houses.
So I think it can be done and solid timber boards might be more suitable than laminated modern boards. Obviously one has to be very careful nailing the boards to the joists so as not to pierce the pipework. Parquet flooring might be more suitable.
My biggest concern personally might be that most of the heat would radiate downwards rather than upwards and there would be lass mass to act as the heat soak/radiator. The result could be similar to undersized radiators.
I have not yet fitted my intended ASHP but plan to use cast iron radiators. I would have thought these would in appearance be appropriate for your 150 year old Vicarage.
I have done this in my 1935 solid walled semi with suspended wood floors and it it working fine for me. Took floorboards up. Insulated between the joists with 100mm kings0am foam board and laid the ufh pipes on top. There were a couple of installation issues.
I was reluctant to notch the joists so put 20mm roofing laths on top of each joist to get the ufh pipes through. This of course raised the floor by 20mm throughout the house.
I did both upper and ground floors. So avoiding an issue on the stairs where building control are rightly extremely fussy about having equal distances on all the treads and risers.
Aluminium spreader plates on the ufh pipes gives a good heat distribution.
Note rooms are very well insulated with up to 70mm pir foam in internal walls and heat pump runs 24/7 . With weather compensation the highest system temp so far seen was 40c at minus 9c outside.
Thanks Nigel, this is very helpful. Sounds like you are getting very good thermal transfer. Can I ask if you have a problem with your floor boards expanding and contracting due to thermal/humidity cycling? If so do you have any good solutions? Much appreciated.
Hi Mark,
I suspect my thermal transfer is rubbish compared with the underfloor
systems buried in a concrete slab.. But it does not need to be able to
supply a lot of heat in a short period, as the heating is on 24/7. Just
trickling in enough heat to replace that lost through the building
fabric.
You will need to tread carefully when it comes to carpets and floor
coverings in general. Probably best of all would be to just polish the
floorboards if they are in good condition. I have used modern Caberfloor
composite boards as the original floorboards had rampant woodworm and
were in a generally bad state. New floorboards would have decimated our
small budget, but looked a lot better. Ended up using carpet tiles with
a low insulation factor, which are stuck with a tackyifying adhesive so
they can be easily removed if required.
So Basically the floor sandwich looks like this. Between each set of
joists, there is a sheet of 100mm thick PIR foam with a foil vapour
barrier facing each side. Itās easily cut to a push fit with an old
woodsaw, but needs to be done individually as joist spacing in an old
building tends to vary, and we are trying to get a push fit. To get an
airtight seal, itās further attached with buildersā foam to close any
gaps and get a good seal. To hold up the foil-backed sheets temporarily
until the builders foam sets there are a few pieces of lath nailed to
the underside of the joists every 3 feet or whatever is convenient.
The areas of foam are then joined across the top of the joists using
aluminium tape so that the floor is completely sealed from the
crawlspace below. Note that you MUST ensure good airflow in the
crawlspace with outside air via the airbricks to prevent potential
moisture and rot problems in the joists as they can no longer dry out
via the house.
On top of the foil on the joists I screwed 20mm roofing laths, 1 per
joist with gaps to route the underfloor pipes between each section. The
pipes sit on top of the PIR sheets held in place with plastic pegs at
the ends where the pipes turn the corner. Aluminium spreader plates are
clipped on and could be screwed to the joists but they can also just sit
there.
The caberfloor sheets are then screwed to the laths on the joists which
gives us a 20mm for the pipes and spreaders. Screws were preferred to
nails as its then possible to take up the caberfloor at a later date or
tightened at a later date if any squeeks arise.
Using flooboards instead of composite panels would probably be better,
as hot air from the 20mm gap would then seep up between the boards,
improving the heat transfer. Since the gap underneath is sealed, there
would be no reason to seal between the floorboards to improve building
air tightness.
Low-insulation carpet tiles finish the job.
While I did all this myself and I am a retired computer programmer, I
suspect professional underfloor heating engineers would be rather
reluctant to do it this way as it is quite time-consuming, not hard to
do but time-consuming.
Beware heating engineers who normally do gas boiler-powered underfloor,
as its a different concept from a different world. Any hint of a mixing
valve then run as you want a low temperature system, not a hot one
blended down. Heat pumps run best with weather compensation, and the
underfloor will spend most of its time at about 30c or lower anyway. A
mixing valve just gets in the way and means you have to run your
heatpump higher just to give the mixing valve something to mix down
with. Even a valve with a thermostat controlling the mix will only end
up duplicating the weather compensation, and if they are not both
singing from the same hymn sheet the result will be chaos.
To answer your couple of questions below about effects from
thermal/humidity cycling. The answer is none that I can tell. Since itās
all running 24/7, there is little or no cycling of anything. And if
there are seasonal cycles, they will be measured in weeks. Temperature
cycles do happen in spring and autumn when the heat demand is so low the
heatpump cannot modulate down low enough, and it has to switch on and
off. Max is about 4-degree variation in system flow temp over several
hours. Not noticeable given the thermal mass of the building.
Regards
Nigel
Thanks Nigel, for sharing your experience, it is much appreciated.
Mark