Heating For Garden Building

[GeoffT]

Having just completed a timber, single storey garden office/workshop building with a pent roof, I'm now looking into heating. Having fed the dimensions (15.4 sqM), location (inner Hebrides) and insulation (good) into a generic calculator, it tells me I should be looking at ~1600 Watts of oil filled electric convection radiator(s).

Thus far I have used an 1800 Watt fan heater and noticed yesterday (not the warmest) that once up to working temperature the inbuilt thermostat was cutting in and out on a roughly 50% duty cycle. Should I perhaps reassess the 1600 Watts prediction?

 

[Murdoch]

Isle of Mull - what a great place to live, we visited a couple of years ago

Did the generic calculator allow you to specify it’s a garden building!

And for clarity what do you mean by 50% duty cycle ?

 

[binky]

If 800w is enough, it's enough. It's fair to say fan heaters tend to warm up quicker. It's also fair to say if you bought a smaller heater and it wasn't enough, it's easy to add another.

 

[GeoffT]

Isle of Mull - what a great place to live, we visited a couple of years ago

Did the generic calculator allow you to specify it’s a garden building!

And for clarity what do you mean by 50% duty cycle ?

Thank you. My wife was born and raised on Mull, left in 1978 to find employment in SE England, we've been visiting ever since, and with retirement (hers, not mine) finally got the chance to move here a couple of years ago.

The calculator was very rudimentary and simply had floor area, location and standard of insulation with no chance to include a type of construction or purpose.

Please note my 'should've gone to Specsavers' edit in the OP. 1800 Watt fan heater. 50% duty cycle? Half the time on, half the time off. So I guess 1600 Watts not far off the mark.

 

[GeoffT]

If 800w is enough, it's enough. It's fair to say fan heaters tend to warm up quicker. It's also fair to say if you bought a smaller heater and it wasn't enough, it's easy to add another.

Please see my edit above. My mistake - it's an 1800 - not 800 - Watt fan heater and runs continually for a couple of hours before the thermostat cuts in.

 

[Andy™]

if you plan to use it often, consider air con instead of electric heaters. they are far more efficient and cost less to run

 

[UNG]

The problem with any external usuable building is keeping some low level heat in them when they are not occupied otherwise a lot of heat and time can be spent getting it back to a comfortable temperature and if used as an office any equipment will be prone to problems and issues caused by damp and condensation

 

[SPECIAL LOCATION]

Am I missing something here??

But isn't "watts" just the power consumed NOT the actual heat output..??

I thought BTU's were the actual heat output... (BTU = British Thermal Units)

Different devices can give higher or lower heat output for the same watts power consumption, dependent upon their efficiency!!

https://www.heatandplumb.com/acatalog/btu-calculator

 

[UNG]

Am I missing something here??

Possibly!!

But isn't "watts" just the power consumed NOT the actual heat output..??

I thought BTU's were the actual heat output... (BTU = British Thermal Units)

This takes me back to my school and college days for some reason the specific heat capacity of water is something that has been stuck in memory
A couple of graphs below for a comparison of watts and BTU's
The first graph has the heat capacity in Kilo Joules for conversion 1 J/s = 1 watt

Different devices can give higher or lower heat output for the same watts power consumption, dependent upon their efficiency!!

I think you answered your own point here the output of a lot of equipment is down to how efficiently it uses what is put in.
LED lamps are a case in point where the lumens / watt can widely vary across lamps of the same wattage

 

[GeoffT]

if you plan to use it often, consider air con instead of electric heaters. they are far more efficient and cost less to run

I did consider an aircon solution, as used at our last house in SE England, where the home office was in a loft space which regularly hit 40+ degrees C in the summer and the primary requirement was cooling/dehumidifying. There I managed to pick up on ebay a new but open-box Mitsubishi split system 150 miles away for £150 plus piping, and got a local AC engineer to vacuum down and gas for a further £100. Happy days. But here not so easy sadly.

 

[GeoffT]

Am I missing something here??

But isn't "watts" just the power consumed NOT the actual heat output..??

I thought BTU's were the actual heat output... (BTU = British Thermal Units)
,
Different devices can give higher or lower heat output for the same watts power consumption, dependent upon their efficiency!!

https://www.heatandplumb.com/acatalog/btu-calculator

Surely with simple electrical resistance heating the conversion efficiency of electricity to heat is as near as damn it to 100%, disregarding any radiation/convection/conduction losses?

 

[Murdoch]

Maybe the answer is to work inside your house when it’s very cold outside

 

[Andy™]

Maybe the answer is to work inside your house when it’s very cold outside

so 11.5 months of the year?

 

[GeoffT]

 

[binky]

Surely with simple electrical resistance heating the conversion efficiency of electricity to heat is as near as damn it to 100%, disregarding any radiation/convection/conduction losses?

That is the general rule, but stuff like heat pump air con or air source heat pumps can offer 3 times the heat output. So 1kw in gives 3 KW out. Obviously they cost far more than a simple heater, but if you are using the building a lot, it could add up for you.

 

[UNG]

so 11.5 months of the year?

Having been to Mull and Oban a number of times it is one of those areas where you can at times experience all four seasons in one day any time of the year. I have seen the weather go from a warm summer day to a full on wintery squall in less than an hour when diving the wrecks in the sound of Mull