Lay underfloor heating by routing into concrete floor?

grandplonker

I have a single story extension, which gets cold in winter.  That's a bummer, because I spend a lot of time there and the radiator is a problem for arranging furniture.  For those reasons, I would consider installing central heating.  Normally, the pipes would be laid by laying new screed on top of the existing floor.  It seems like a lot of hassle when the floor is already solid, and insulated properly.

Can I lay the heating pipes by using an electric router to dig a zigzag trench across the room, lay the pipes and fill it in?

I'm very handy.  I've worked on heating systems before and up for a challenge.  I haven't laid UFH before.

Thoughts?

FreeBear

grandplonker said: Can I lay the heating pipes by using an electric router to dig a zigzag trench across the room, lay the pipes and fill it in?

You will not be able to cut the slots effectively with a conventional router & bit - The screed will kill a carbide router bit in seconds, and the dust generated will make short work of the router. There are industrial tools designed for this sort of task. Expensive, but you might be able to hire one. An alternative would be a chaser as used for cutting slots in a wall for conduit. Very dusty, dirty work, but with the aid of an SDS drill & chisel, you could get some neat slots.

Another option is to call in a contractor that has one of those UFH slot cutting machines. No idea how much they would charge though.

grumbler

Does the concrete floor have proper insulation underneath?

ComicGeek

Depending on size, and how often you use the space, I would consider installing an electric mat system such as from Rayotec or similar. Can be expensive to run, but much cheaper and easier to install than a wet system. Depending on size and amount of use, it might be cheaper in the long run. You'll still need about 10mm for the rigid insulation boards (yes, you'll still need them!) and the mat and liquid screed over.

Or, if you can get away with a bigger change in floor levels, you can get routed chipboard options or low profile systems like https://www.underfloorheating.co.uk/profi-low that have been designed for the retrofit market.  

grandplonker

FreeBear said:

There are industrial tools designed for this sort of task. Expensive, but you might be able to hire one. An alternative would be a chaser as used for cutting slots in a wall for conduit. Very dusty, dirty work, but with the aid of an SDS drill & chisel, you could get some neat slots.

Thank you, I will look into this.  I don't have any deadlines (it's my own house) so I can take my time over this project.

@FreeBear what do I call a machine like this?  Would they be stocked by hire places like HSS?

grumbler said:

Does the concrete floor have proper insulation underneath?

Yes.

ComicGeek said:

I would consider installing an electric mat system such as from Rayotec

Thank you for the suggestion, but absolutely no chance.  Electric is four times the price & carbon emissions of gas. At that rate, there will be so much global warming I'll not need central heating.

Or, if you can get away with a bigger change in floor levels, you can get routed chipboard options or low profile systems

I can get away with a raise in floor level.  How would it compare to the price, or ease of doing it?

FreeBear

grandplonker said:  what do I call a machine like this?  Would they be stocked by hire places like HSS?

An "UFH milling machine" or "UFH slot cutter" - Not seen any in places like HSS, but you might find someone willing to hire.

ComicGeek

grandplonker said:

I would consider installing an electric mat system such as from Rayotec

Thank you for the suggestion, but absolutely no chance.  Electric is four times the price & carbon emissions of gas. At that rate, there will be so much global warming I'll not need central heating.

Or, if you can get away with a bigger change in floor levels, you can get routed chipboard options or low profile systems

I can get away with a raise in floor level.  How would it compare to the price, or ease of doing it?

Electric is much more expensive to run, yes. But then you need to compare the capital costs as well, as sometimes it can still be cheaper in the long run, look at the whole cost comparison. With the wet underfloor heating you'll also need to find somewhere for the manifold and other gear.

In terms of carbon emissions, there are lots of different measurements floating around at the moment, but the latest from draft Building Regs documents has electricity at 0.233 kgCO2/kWh and gas at 0.210 kgCO2/kWh. Taking into account the average efficiency of a very new condensing gas boiler, the two are virtually the same. So in terms of global warming, there is probably an argument that electric heating is actually the most environmentally friendly option, particularly as the national grid is becoming increasingly decarbonised - while the mains gas figure is likely to keep increasing, the electricity figure should keep decreasing. 

In terms of the UFH systems, they are normally more expensive and simple, or less expensive and complicated. You need to pick which one is more important for you. Underfloor heating pipework is very easy to install, but it's important to get the design right - heat loss calculations to determine required heat output, pipework layouts to determine spacing between loops and number of circuits. Protecting the pipework during installation and pressure testing before covering etc. 

The best company I've worked with is Robbens Systems https://www.underfloorheating.co.uk/ - technical team are extremely helpful and they have a wide range of solutions for all different floor types and installation methods.

grandplonker

In terms of carbon emissions, there are lots of different measurements floating around at the moment, but the latest from draft Building Regs documents has electricity at 0.233 kgCO2/kWh and gas at 0.210 kgCO2/kWh. Taking into account the average efficiency of a very new condensing gas boiler, the two are virtually the same.

My mistake - I was thinking of an air source heat pump, which done properly is much lower carbon than electric UFH.  In any case, I'll be sticking with a wet system.

knightstyle

You must find out why this room is so cold in winter.  Check insulation in the ceiling and walls, it is far better to improve insulation than to install expensive underfloor heating.
Remember that a perfectly insulated room needs no extra heating, just the heat given off by our bodies and things like light fittings.

FreeBear

knightstyle said: Remember that a perfectly insulated room needs no extra heating, just the heat given off by our bodies and things like light fittings.

A modern LED light will consume 5-10W of energy. 50-60% of this will be given off as heat..

A human body generates around 100-120W of heat, not a lot, but if you plug enough of them in to the grid...

If there is scope to improve the insulation of the room, it is certainly something to consider as part of a refurbishment. It is something I have done to a small room recently (solid brick wall, internal wall insulation), and coupled with a new window, it has made for a dramatic improvement. So much so, I have gone from a ~1200W radiator down to a 500W.

grumbler

FreeBear said:

  50-60% of this will be given off as heat..

I guess the most of remaining 50-40% becomes a heat eventually too (excluding the light that escapes through windows.

Not that it makes any significant difference...

ETA: I think it can be assumed that all electric power consumed by a house heats it with efficiency close to 100%.