Have I selected the right heater?

Hi,

I'm wondering if I could get some opinions and help on one of our Herschel IR heater setups.

We're already using Herschel IR heaters to heat rooms in our home.

Recently, I bought a Select XLS 600w unit to heat an outbuilding that we use as a studio workspace. 

The outbuilding is brick-built to building regulation standards, with underfloor, wall and ceiling insulation. It has an apex roof and is typically left unheated. I only turn the heating on when we go to use the building.

The room is long and narrow, with the Select XLS 600w unit attached to the wall – as you can see from this photograph.

Unfortunately, after turning on the heating, the Select XLS seems to be taking far too long to heat the space. As a result, we're left shivering for long periods of time.

For example, today I entered the studio and the building temperature was just under 10c. I turned on the Select XLS and almost three hours later, the temperature is still only 13.5c.

I suspect the issue is one of two things:-

* I may have undersized the heating requirements. Or, perhaps I've placed the Select XLS in the wrong position at floor level in a room that has chairs and furniture?
* We have a PIR sensor that turns on/off the IR heating based on movement. I did this to prevent us heating an unused room, but could we have this setup incorrectly?

Thoughts and advice welcome!

Richard Tubb.