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A few questions about an urgent DIY UFH install over chipboard flooring

Paene Finitur

By Paene Finitur
in Underfloor Heating

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Paene Finitur Member

Paene Finitur

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I'd asked my electrician to lay a small underfloor heating circuit in one of the bedrooms, but despite being told months ago, he hasn't got the job done and I've decided to step in and do it myself as the floor is being laid on Thursday, so time is of the essence. Naturally, the sparks has at least agreed to check and sign off my work. 

 

Reason for going for UFH in this case is that the floor in question is a little annex which juts out over a porch so gets no rising heat from downstairs and is only 3.5m2 so a small UFH install here should be fairly simple, I'm thinking. I'm wondering if anyone has experience of this and can answer the following questions.

 

First question: I've been working mainly from this video which seems comprehensive although, like most other videos and tutorials, it assumes that you're installing over a screed. From what I can gather, it should be much simpler over chipboard - especially if you're using engineered wood over it, as I am, rather than tiles - being just a matter of first laying an appropriate insulation board such as this one, and then fix the mat onto the insulation board as per video/instructions. Should the insulation boards be glued/fixed in some way to the chipboard, or just float free? I guess any type of appropriate insulation would do?

 

Second question: I was planning, for simplicity, to get a kit something like this Nassboards one. I assume I'll need:

  • Heating Mat
  • Thermostat
  • Floor probe and conduit
  • Thermal primer and roller

 

Anything else I would need, or does this seem reasonable?

 

Many thanks!

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ProDave Advanced Member

ProDave

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Don't rush this.  Lets check some facts before you do this in haste and make a big mistake.

 

So this is a small annex above a porch and you want UFH.  FIRST check there is a GOOD level of insulation under the floor.  The 6mm insulation board you linked to is NOT enough.  So first tell us what is under the chipboard that is going to stop most of the heat from this UFH just being lost down and out through the porch below.

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Paene Finitur Member

Paene Finitur

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10 minutes ago, ProDave said:

So first tell us what is under the chipboard that is going to stop most of the heat from this UFH just being lost down and out through the porch below.

A fair question. The joist voids are packed with Xtratherm PIR rigid insulation board (I've a feeling at might be 100mm though it could be more) and the ceiling of the porch is 12mm ply.

 

This is in a new build, by the way.

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markc Advanced Member

markc

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Electric UFH is not like wet. Water running through pipes is at a constant temperature and limits floor temp. Electric heater wire does not self regulate so anything left on the floor creates local hot spots (ask my cat). 

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Nickfromwales Advanced Member

Nickfromwales

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Just now, Paene Finitur said:

It's engineered oak. The supplier and have confirmed that it can be used with UFH.

OK. The issue often overlooked is with soft insulation boards used under the electric UFH and then furniture feet etc or other point loads cause the insulation to compress at that point as the floor covering isn't spreading the load enough. Engineered wood will be fine.

How often will this be used? It will be relatively crap in heating the room, and bloody expensive to run. Is this in conjunction with a radiator in this room so is auxiliary heating only, or is this intended to heat a room by itself? 

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Paene Finitur Member

Paene Finitur

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3 minutes ago, JohnMo said:

Room 3.5m2, why would you bother with UFH, seems a complete waste of time. Just stick a small radiator or panel heater in there.

 

Is a room that size even usable - its a cupboard.

 

It actually is a cupboard. The room was originally specced as a box room but the Velux was too high to meet fire regulations, so some of the back of a very large cupboard in an adjacent room was borrowed to create a little ante-room. It has another Velux in it (this one meets FRs) and works well as a little study annex. I considered a panel heater but as you mention, space is limited.

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Paene Finitur Member

Paene Finitur

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Just now, Nickfromwales said:

Why are you heating this space?

OK. It's not now a cupboard. It was space taken from a cupboard. It is going to be used as small office. I'm heating it because it has no source of heating and it is also above a porch, as I mentioned.

 

Quote

FYI, there are different temp kits giving higher or lower w/m2. Have you calculated this?

My calculations came out at about 300w for the room. The kit I linked was about 200/m2 so probably a bit much. That said, I can't find a great amount of choice in UFH kits for this size of mat. It is connected to a thermostat which should tend to mitigate things.
 

Quote

How often will this be used? It will be relatively crap in heating the room, and bloody expensive to run. Is this in conjunction with a radiator in this room so is auxiliary heating only, or is this intended to heat a room by itself?

I expect it to be on timed, running for a short period early evening to take the chill off the floor. Why would it be crap? There are no other heating sources (other than a PC perhaps) and space is at a premium for radiators.

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Nickfromwales Advanced Member

Nickfromwales

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2 minutes ago, Paene Finitur said:

OK. It's not now a cupboard. It was space taken from a cupboard. It is going to be used as small office. I'm heating it because it has no source of heating and it is also above a porch, as I mentioned.

OK, thanks.

 

3 minutes ago, Paene Finitur said:

My calculations came out at about 300w for the room. The kit I linked was about 200/m2 so probably a bit much. That said, I can't find a great amount of choice in UFH kits for this size of mat. It is connected to a thermostat which should tend to mitigate things.

OK, so a room off an otherwise already heated room? Or a doorway between the two spaces? Assuming 3 external walls, an adversely cold floor, and the height plus Velux.

 

200w/m2 is quite an aggressive in terms of UFH, so you'll likely get under and over shoot, exacerbated by the floor temp probe and the room stat both trying the manage that heat input to floor vs heat getting to space scenario ( so they'll be constantly squabbling tbh ).

 

14 minutes ago, Paene Finitur said:

I expect it to be on timed, running for a short period early evening to take the chill off the floor. Why would it be crap? There are no other heating sources (other than a PC perhaps) and space is at a premium for radiators.

Heating the room ( space ) will require turning this on a good while before using the space, so you'll need a self-learning stat like the Warmup 3 or 4iE / other stat / controller that offers that feature aka "setback". These work out how long it takes from inputting energy into the floor to getting the air temp of that space to the required stat temp ( 20.5oC for eg ) and it then alters the switch on time to allow it to come on sooner than the timer is actually set for. It will be very slow to react, will overreact due to the minimal 'thermal content' of the heated emitter ( you wooden floor ) so really not advisable.

 

You'd be FAR better off with a tiny oil filled radiator, which will heat that space up pretty much instantly and waste next to no heat.

 

Hopefully I have helped you understand why this is a bad idea. 

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Nickfromwales Advanced Member

Nickfromwales

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300w you say?

 

£14

 

https://www.amazon.co.uk/winnerruby-Portable-Electric-Travelling-Efficient/dp/B08LNMHCZW/ref=asc_df_B08LNMHCZW/?tag=googshopuk-21&linkCode=df0&hvadid=554322167175&hvpos=&hvnetw=g&hvrand=8526765289628865508&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1007460&hvtargid=pla-1458892795428&psc=1

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saveasteading Advanced Member

saveasteading

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19 hours ago, JohnMo said:

Room 3.5m2, why would you bother with UFH

We revamped an en-suite and installed an electric blanket on a very thin sheet of insulation.  Tiles above.

It works very efficiently with timer and temperature control and stays warm long after it has gone off.

It is a luxury though, for the sake of warm feet on a tiled floor. 

Why?  It is nice and  my wife loves it.

Why not? Expensive.

An electric booster to the towel rail is another welcome addition. Push the button and it dries the towels then switches off, and so saves the boiler running.

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Nickfromwales Advanced Member

Nickfromwales

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5 hours ago, saveasteading said:

We revamped an en-suite and installed an electric blanket on a very thin sheet of insulation.  Tiles above.

It works very efficiently with timer and temperature control and stays warm long after it has gone off.

It is a luxury though, for the sake of warm feet on a tiled floor. 

Why?  It is nice and  my wife loves it.

Why not? Expensive.

An electric booster to the towel rail is another welcome addition. Push the button and it dries the towels then switches off, and so saves the boiler running.

Agree totally, but it is not the same, at all, for the same system with a wooden floor for space heating. 
The OP does that ask for warm feet, they are asking for space heating, so I was very specific in how I replied.

Wood doesn’t ‘retain the heat’ like tiles do, and as such makes a very poor, near sporadic emitter of heat.

Bathrooms also get tolerated when just a little “too warm” whereas this space will become nigh on intolerable in the same situation. 
Apples and oranges I think. 

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SteamyTea Advanced Member

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12 hours ago, Nickfromwales said:

Wood doesn’t ‘retain the heat’ like tiles do,

Oak has an SHC of 2 kJ/kg.K

Ceramics are around 0.8 kJ/kg.K

Oak has a specific density of around 750 kg/m3

Ceramic around 2300 kg/m3

 

So pretty similar once thickness is taken into account.

 

The conductivity of oak 0.17 W/m.K

Ceramic 1.5 W/m.K

 

If you know the thickness of each, you can easily work out the real difference.

 

Be better to say that wood does not conduct heat like ceramic tiles do.

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Nickfromwales Advanced Member

Nickfromwales

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4 minutes ago, SteamyTea said:

Oak has an SHC of 2 kJ/kg.K

Ceramics are around 0.8 kJ/kg.K

Oak has a specific density of around 750 kg/m3

Ceramic around 2300 kg/m3

 

So pretty similar once thickness is taken into account.

 

The conductivity of oak 0.17 W/m.K

Ceramic 1.5 W/m.K

 

If you know the thickness of each, you can easily work out the real difference.

 

Be better to say that wood does not conduct heat like ceramic tiles do.

Thanks, Obi Wan. Upgraded from laymen’s terms to science in one swing of the pen. 👌

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