For consideration if building new workshop

[Spectric]

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.

 

[Cabinetman]

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?

 

[shed9]

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.

 

[Spectric]

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.

 

[Spectric]

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.

 

[Adam W.]

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

 

[Droogs]

☝ perfick for making things for the modern home

 

[shed9]

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.

 

[Spectric]

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.

 

[Droogs]

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

 

[mikej460]

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.

 

[Ollie78]

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

 

[Woody2Shoes]

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.

 

[Doug B]

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.

 

[AlanY]

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.

 

[TominDales]

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.

 

[Spectric]

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.

 

[Ollie78]

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

 

[mikej460]

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.

 

[Doug B]

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.