I definitely want the floor heated, I suffer badly with cold fingers so want a comfortable workshop. Also, will,likely be spraying paint in There so want as little air movement as possible.

The doors have a u value of 5.2W/m2K and are 3.5m by 2.5m.

The roof ceiling is apex type, with insulated bords that interlock and then are sealed. U value 0.14m2 I believe.

and the walls 13blocks high and same u value as roof.

Floor will have 100mm kingspan underneath.

Floor will be 100mm concrete with steel cube reinforcement and UFH pipes cable tied to it.

Can anyone put that through a calc and see what it comes out with?

Cheers

Steve

What size are the blocks, if 220 x 440 then the height would be 2.86m in block plus say 0.12 for mortar giving near enough 3m, but your door is how high 2.5m?

No indication of roof slope, so I will assume 45 degrees.

Area of walls = 4 x 5m x2.5m + (5m x 2.5m gables) - 2.5m x 3.5m = 50 m2 + 12.5m2 -9m2 = 52.5m2

Area of roof = 25m2 x 1.4 = 35m2

Total area around 90m2.

Area of door = 2.5x3.5 = 9m2

Heat loss = 90 x 0.14 W/K + 9 x 5.2W/k = 12.6 + 46.8 = 59.4 W/K (call it 60 for ease of calculations)

So if it was -3C outside and say 22C inside that would require 25 x 60 = 1500W

That excludes the heat loss from the floor into the earth, but it is obvious that the door is the major problem, without it you would be around 1/4 of the heat loss.

Someone else should check my calculations.

Can you do any better on the door as that amount of heat loss will cause significant air movement in itself. You may also find that opening the door will cause a rapid change in temperature inside that causes air movement and takes some time to restore the temperature.

Does the door have a normal size opening for you to get in/out which would reduce the problems?

.

Not sure where you are in the country, but if you assume an average of 10C over the year and the workshop heated to say 20C 7 days a week, then you will be looking at : 10 x 60 x 24 x 365 Whrs pa. so around 6000kWh pa. You can put more accurate figures in to the calculations , but that sounds reasonable to me. Of course there will be other heat added internally, from people working, equipment running (will the compressor be inside?) etc. The average temperature is not a good measure as you will need heating whenever the outside temperature is below say 15C, but not when it is above unless unoccupied for long periods, but when the temp is above 20C it will affect the calculation for average temperature but there is no corresponding cold period for the temperature.

You could try using degree days to get a value, but that is dependant on what you set as a base temp ie. the lowest outside temperature at which you need no heat inside.

HTH

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Using your new figure of 8m x 8m:

Roof about 90m2, walls about 80m2 so around 72W/K, so at 25K difference that would be near 1800W, or 9000KWh pa