Converted Garage - how to heat it

My wife runs a registered childminding service,recently we converted the garage to cater for after school children. Our big problem is heating,there is a radiator in there from when the garage was built. It works fine,but to room only needs to be heated from 2-5pm each day.
There is an extension to the side of the house in which she caters for the pre-school children,this is heated in the morning as it is needed from 7pm - 5pm,but doesn't need any heat in the afternoon as there is alot of glass in the room and it gets the afternoon sun.At present she has to turn on the heating system in the afternoon just to heat the converted garage,this then makes the other room too warm.
We could use an electric heater but this could prove very expensive given the cost of ESB,anybody got an ideas ?.

Why not swap the pre-school children to the converted garage and the after school to the extension

Thought about that at the time,would have meant having to put in a "sleeping room" and "napping changing room" and we didn't have the required square footage to do this.

Turn off the radiator in the room that is too warm this can be done by closing the rad valves, the other rooms will heat but the room with the rad closed off won't.

Good Luck

Dobber22.thanks for reply
This would mean turning all rads off in the house,e.g kitchen,hallway,sleeping room,etc. which is not practial ever day. Also,the burner would be running solely to heat on room,still not ecnomical.

You may need to re-insulate the converted garage. You can get these 30-40mm thick insulated plaster boards for the walls and ceiling.

When the garage was built originally (about 6 years ago), we used stanadard aeroboard insulation in the cavity wall and all internal walls and ceiling were plastered. Basically,we built it thinking we may need it as a habitable room in the future.
Our problem now is heating it,has anybody got one of those ESB storage heaters,are they any good?

What about a Gas super ser heater? they are cheap enough to run you just buy another bottle of Gas when it runs out only problem is you'd have to keep the kids away from the front of it with a barrier of some sort maybe a good strong folding firegard would be enough.

just a thought.

You need a modulating boiler,preferable a condensing boiler.A modulating boiler fires only as much fuel as it needs to satisfy demand.Compare the boiler that you have with what is available at http:www.sedbuk.com .You can figure out yourself what the pay back time for the investment would be by asking your boiler shop or the manufacturers for a price. And of course it makes sense to install automatic radiator valves.Better ones are vandal proof-that would eliminate the little hands with interfering .These are used commonly in schools and other public places.Ask in the plumber shop.About € 20-30 ,for a vandal proof one about €40.- . Maybe a simple device attached to your old boiler would make sense as well.A "night reducer",that is a thermostat that reduces the flow temperature during a preset time-whenever you need it,not just at night time.This device would be exchanged with the thermostate that is at the boiler,a job of two minutes for costs of around €20-30. Additionally you could install a larger or a second radiator in the room with the lowest heat demand (which would be your creche),that would allow you to reduce the flow temperature (what comes from the boiler) and still maintain the same output in the room-either manually at the boiler thermostate or with the aid of the "night reducer thermostate "
heinbloed