# For consideration if building new workshop



## Spectric (6 May 2021)

Hi all

Well having just done some design work on the electrical installation for someones new workshop I have realised that a lot of people may have left the heating aspect to late in the design process. On this project everything was layed out before any actual work was started, that included lighting, heating, thermal and everything else. If you are having a concrete base then a good solution for your heating needs is simply underfloor heating, with a three inch screed over the heating wires you end up with a large thermal mass, which is how I heated a conservatory in my last house but never linked workshops to this means of heating. This system works best if left on with a timer/stat so the slab remains warm, uses much less energy and as the workshop is always warm you do not suffer damp or rusty tools. The other bonus is that no internal space is lost to heating and because the heat is feet up you don't need walk boards as the floor is warm. So for anyone contemplating a new build then you should give this some consideration, if I was doing a new build it is the way I would go as it is a cheap and cost effective solution.


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## Cabinetman (6 May 2021)

Hi Roy, I think a lot of people including me I’ve always been told that underfloor heating is expensive to run – ( I’m quite willing to be converted) not an option in my case but in future I shall certainly consider it. How do the running costs compare to the same building but with an insulated wooden floor and, say electric oilfilled radiators? Or is it the same once you have heated up that mass?


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## shed9 (6 May 2021)

It tends to be favoured for small areas or where water based PEX systems are not viable but I would have thought electrical UFH would be too power hungry for the large expanse of a workshop slab. That said, like Cabinetman I'm also willing to be converted on the idea if there is something I'm missing.


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## Spectric (6 May 2021)

Once upto temperature the mass holds the heat, it then just maintains that temperature so the running cost can be reasonable. The floor insulation is below the heating wires so you get a really warm and cosy feeling and no cold, dampness and you just turn the stat down when you are not there to keep background warmth. This new workshop is considering either underfloor electric or a gas radiant tube heater above but that loses potential space whilst giving instant heat.


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## Spectric (6 May 2021)

shed9 said:


> too power hungry for the large expanse of a workshop slab



The power usage depends on the spacing of the heating wires, you do not completely cover the area if there are units, cupboards or machinery there, so for a workshop you would only put the heat where there is open floorspace. In housing the water systems are more favoured but that means a gas boiler and a lot more cost etc etc.


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## Adam W. (6 May 2021)

UFH creates a very dry environment and will drive down the MC of your timber to 8% or less.


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## Droogs (6 May 2021)

☝ perfick for making things for the modern home


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## shed9 (6 May 2021)

Spectric said:


> The power usage depends on the spacing of the heating wires, you do not completely cover the area if there are units, cupboards or machinery there, so for a workshop you would only put the heat where there is open floorspace. In housing the water systems are more favoured but that means a gas boiler and a lot more cost etc etc.


I've fitted UFH to the ground floor of my own home and as we are quite rural the boiler runs of LPG however I also have another space where I have fitted electrical UFH and the cost efficiencies of that don't stack up to that of the LPG which is a lot more cost effective. From a heating perspective UFH is great I'm just not convinced that kW's can out compete with BTU's based on my own experience of both.


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## Spectric (6 May 2021)

In a domestic property I would always say you need to avoid electric heating in any form, but in a workshop where there is a smaller footprint and you don't want the expense of a boiler then electric can work out ok so long as you have the heating wires embeded into the screed on top of the concrete to provide a thermal mass. The electric systems where they have a low build profile often for installation after the floor has been laid are not that cost effective, you have no storage. In my last workshop I installed a gas boiler and three radiators because it was for me an easy job and that worked really well, but no labour cost and all trade prices. These days in my small garage workshop I use a portable oil filled electric radiator which works fine to take the chill out of the air, that is reasonably cheap to run again because of its storage ability. Not sure of the cost of the large LPG cylinders these days but without gas your options are limited although I know a few people running pellet burners to good effect.


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## Droogs (6 May 2021)

What do these Electric UFH systems typically use powerwise, would an average sized solar array on a house be enough to keep them going?


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## mikej460 (6 May 2021)

The problem with electric UFH is the warm up time of the concrete slab and that you need very good insulation to reduce heat loss.


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## Ollie78 (6 May 2021)

The guy in the unit next to me is doing an interesting thing with his underfloor heating, he has got hold of a large air conditioning unit (so a big heat exchanger basically) he is going to hook this up to his newly installed UFH which is pex pipe. The heat exchanger will basically scavenge a lot of heat for very little money and put a base level of warmth into the system, he then has an instant electric water heater (we are not on mains gas) for boosting it to the required temperature.
He has done all the maths and reckons it will be dirt cheap to run once its set up.

Ollie


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## Woody2Shoes (7 May 2021)

An interesting idea. I always think that wires or tubes embedded in screed/concrete are a hostage to fortune - sooner or later they'll break/leak/clog. I think that the overall energy efficiency will depend on the levels of insulation in the superstructure and on the 'intelligence' of the control system.
I'm not on mains gas and see that the power grid is decarbonizing, so electric heating is increasingly attractive from that point of view. I think that a well insulated building with a high thermal mass/inertia which is designed to maximise solar gain is the ideal, as it shouldn't need much heating or cooling in our climate.


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## Doug B (7 May 2021)

With sealed system boilers such as combi boilers etc it quite easy to run a couple of radiators off the house central heating system even if the workshop is detached from the house, so no need for a separate boiler.
My own workshop is 10 metres from the house it has 3 small rads which keep the shop nice & warm with the added bonus that I didn’t notice any particular rise in the gas bill after installing them.
As has been mentioned insulation is key if you are going to install heating but for me this was already a major consideration when I built the workshop as it is in a domestic setting & I didn’t want to disturb the neighbours.


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## AlanY (7 May 2021)

Ollie78 said:


> The guy in the unit next to me is doing an interesting thing with his underfloor heating, he has got hold of a large air conditioning unit (so a big heat exchanger basically) he is going to hook this up to his newly installed UFH which is pex pipe. The heat exchanger will basically scavenge a lot of heat for very little money and put a base level of warmth into the system, he then has an instant electric water heater (we are not on mains gas) for boosting it to the required temperature.
> He has done all the maths and reckons it will be dirt cheap to run once its set up.
> 
> Ollie


I use an air-source heat pump (which is exactly what your friend has in his aircon unit) to heat the swimming pool. For every 2.5 kWs I put in the device outputs 9kW to the pool. I think modern heat pumps are even more efficient.


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## TominDales (7 May 2021)

Seems a good idea. My feet get absolutely frozen in winter, to the extend I bought a heated floor mat from China..... For a workshop that does not need to be at full temperature this seems a good solution. I wonder if I could retrofit to my garage concrete floor? That is raise the floor a few inches.
Direct electric or heat pumps are going to be the far more available as the country/world decarbonises. There are some schemes to replace natural gas with hydrogen, but I suspect heat pumps will be the dominant technology, and prices will fall as manufacturing rates shoot up.


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## Spectric (7 May 2021)

Ollie78 said:


> he then has an instant electric water heater (we are not on mains gas) for boosting it to the required temperature.


The actual water temperature is about 50° C in underfloor heating and is why you have a pump and mixer valve, the pump keeps the water flowing continously to ensure even heat. They work very efficiently with a condensing boiler because with a low feed temperature it is easy to keep the return flow low. So with an electric water heater you need to ensure the stat can be set low enough, you may find that it cannot because of legionella regulations.


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## Ollie78 (7 May 2021)

Spectric said:


> The actual water temperature is about 50° C in underfloor heating and is why you have a pump and mixer valve, the pump keeps the water flowing continously to ensure even heat. They work very efficiently with a condensing boiler because with a low feed temperature it is easy to keep the return flow low. So with an electric water heater you need to ensure the stat can be set low enough, you may find that it cannot because of legionella regulations.



I am not sure of the exact details of his electric heater but it is quite specific and he got it from somewhere in Europe if I recall. 
I think it should be getting installed before winter hits, I am intrigued to see how good it is. I'll ask him about the expected operating temp.

Ollie


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## mikej460 (7 May 2021)

Spectric said:


> The actual water temperature is about 50° C in underfloor heating and is why you have a pump and mixer valve, the pump keeps the water flowing continously to ensure even heat. They work very efficiently with a condensing boiler because with a low feed temperature it is easy to keep the return flow low. So with an electric water heater you need to ensure the stat can be set low enough, you may find that it cannot because of legionella regulations.


As I understand it Legionnaires only affects directly heated water which must be 60 degrees or higher to kill the bacteria. Modern indirect water heaters aren't affected as the mains cold water is heated by the stored (but not used) hot water on an as needed basis.


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## Doug B (8 May 2021)

I found this calculator for electric underfloor heating costs Electric Underfloor Heating Running Cost Calculator | ThermoSphere

I can’t tell how accurate it is, it seemed strange that a bathroom was cheaper than a living room & dining room to heat, our bathroom is the warmest room in the house.
That said it predicted it would cost £2.34 for a 6 hour period to heat my workshop classing it as a dining room & £2.17 if it was a bathroom. Now I appreciate I wouldn’t want the workshop as hot as domestic rooms but chances are I would need to heat it longer than the 6 hour period each day.
With those kind of figures for a month I’d be looking at a higher price to heat the workshop than I pay for gas to heat the workshop & a 3 bedroom house.


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## Woody2Shoes (8 May 2021)

Doug B said:


> I found this calculator for electric underfloor heating costs Electric Underfloor Heating Running Cost Calculator | ThermoSphere
> 
> I can’t tell how accurate it is, it seemed strange that a bathroom was cheaper than a living room & dining room to heat, our bathroom is the warmest room in the house.
> That said it predicted it would cost £2.34 for a 6 hour period to heat my workshop classing it as a dining room & £2.17 if it was a bathroom. Now I appreciate I wouldn’t want the workshop as hot as domestic rooms but chances are I would need to heat it longer than the 6 hour period each day.
> With those kind of figures for a month I’d be looking at a higher price to heat the workshop than I pay for gas to heat the workshop & a 3 bedroom house.


That calculator seems to take no account of how well insulated the room is, which means its "output" is pretty much a vague guess, but yes you're right.


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## Adam W. (8 May 2021)

Electric UFH is cheap to install and has a slim profile which makes it convenient for renovation work, but water UFH is much more expensive to install and far cheaper to run.

In renovation work for private customers, the only thing that seems to matter is the cost of installtion, which is why it's a popular system.


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## TRITON (8 May 2021)

How does putting 100-400kg of weight on 1-2sq meters work with underfloor heating ?. I'd have thought the especially heavy machines would possibly affect it.

My old boss's take on being cold... Work harder.


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## Adam W. (8 May 2021)

Use a reinforced concrete slab and don't put the pipes under the machine.

Here in Denmark they put the UFH pipes in the slab tied to the reinforcement, pour the slab and build all the partition walls on top of it all. They have about 2 1/2' of polystyrene underneath the lot with no DPM.

It seems odd to me, but that's the way they build all the new houses. And to be honest, I don't think I'd like UFH in my workshop, as it'll be too warm and also play merry hell with the timber.


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## Doug B (8 May 2021)

TRITON said:


> How does putting 100-400kg of weight on 1-2sq meters work with underfloor heating ?. I'd have thought the especially heavy machines would possibly affect it.
> 
> My old boss's take on being cold... Work harder.


I used to work in a workshop with UFH albeit water not electric it had a felder combination machine in there which was certainly very heavy but it was no detriment to the heating.
On a freezing January day it was bloody lovely working in there, it had a stat to control the temperature so it was never too hot I’d certainly consider UFH if I was to build another shop, not that that is likely to happen.


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## Soylent1 (9 May 2021)

Just this last week my little 3.5 x 4 workshop has had the electrical work connected up. 

8 x double sockets 
4 x 4200 lumen led batton lights 
And electrical under floor heating 

100mm celotex in the roof 
150mm limecrete slab on 150mm glaster insulation 
50mm celotex in the walls
12mm OSB for the walls 

So far I've set the thermostat at 16 Celsius and it's maintained the same temperature for the last 48 hrs. 

I installed the electrical UFH as an experiment really, I think it was about 200 quid as I was doing the floor slab anyway I thought I'd give it a try. 

From memory the electrical UFH is 1200w so just a background heat I suppose. I'm going to leave the stat at the same temperature and monitor the bills. If it turns out to be costing a bomb I'll just turn it off, but for the time being I'm quite confident that it's maintaining the temperature quite efficiently, but I'll see what happens when the weather gets cold.


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## clogs (9 May 2021)

my 2 story 4 bed house is heated with a wood or oil burning boiler.......will never burn oil......
all the pipes to the rads are under the concrete floors......
radiators here are very expensicve comp to the UK......
so why bother with rads at all, just a little more piping would work a treat......
u can easily find the warm spots in the floor as there's always a cat sleeping on it.....hahaha......
This winter we bought 1 ton of Olive wood and any rubbish we found around the place....the first winter we burnt 2 ton.....
at 130 euro's per ton....not bad for heating and hot water....admitadly winter is 6-8 weeks long.....
we evan had a frost one morning......hahaha......
the rest of the year all hot water 300ltrs is free by solar panels.....
just got to make solar panels for the s/pool now.......

ps, anyone for putting UFH in a building use high density foam norm blue in colour.....not the norm expanded polystyrene sheets....


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## Spectric (9 May 2021)

Soylent1 said:


> I installed the electrical UFH as an experiment really, I think it was about 200 quid as I was doing the floor slab anyway I thought I'd give it a try.


How much screed on top of the wires? 



clogs said:


> admitadly winter is 6-8 weeks long


Lucky you, we have a 6 to 8 month winter here and if it gets to 24°C in mid summer we are into a severe heatwave.


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## Soylent1 (9 May 2021)

Spectric said:


> How much screed on top of the wires?
> 
> There's about 2" screed on top. The system I installed isn't really designed to work in the way I'm using it - to heat a slab as a thermal bank but it seems to be working at the moment. I think the most important thing is having a well insulated space.


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## Spectric (9 May 2021)

Yes insulation is key, otherwise a lot of heat warms the sub base but your system may take longer to heat the slab but it will get there providing the heat loss is minimal and I found it to be a nice feeling having warmth from the bottom up.


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## Woody2Shoes (10 May 2021)

Spectric said:


> Yes insulation is key, otherwise a lot of heat warms the sub base but your system may take longer to heat the slab but it will get there providing the heat loss is minimal and I found it to be a nice feeling having warmth from the bottom up.


There's very definitely a psycho-/physiological benefit to UFH!


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