When is it ethical to change your radiator valve? That was the big question that was perplexing the Newsnight team after our broadcast last night.

The housing minister, Yvette Cooper, invited me to have the first of the new Energy Performance Certificates on my home and even did me the honour of popping round to my house for a cup of tea to see how I got on.

It should have been a pretty straightforward report. Trials of the certificates begin around the country next week. They'll be introduced nationwide in June next year.

The idea is pretty simple. When houses are sold the seller will pay for the house to be energy rated, just like a fridge, and they'll offer suggestions for how energy efficiency could be improved. Sounds pretty sensible doesn't it?

My house scored a D just below average but not bad for an older building. (Read the certificate for yourself.) It said I could boost that to a respectable C with a few relatively cheap improvements.

The big one was filling the cavity in my walls - my certificate claims that'll save £56 a year. The only reason I haven't already done this is that I¹d been told I didn¹t have a cavity to fill.

The other home improvement is the one that proved controversial. Apparently I'd be able to save £21 a year by improving the programmer on my boiler and putting in something called thermostatic valves on my radiators.

I asked my friend Laurence, who's a plumber, to come round and give me an estimate. He was very sceptical that the switch was worthwhile.

I've already got valves on my radiators and Laurence's view was that I'd be replacing a perfectly good valve he'd have to charge me 300 notes for the service.

Of course there would be a small carbon saving because the thermostatic valves are easier to use but there'd be a carbon cost too - all the energy and materials needed to make the things.

It didn't sound like a good deal to me.

But not everyone agrees. After the programme was broadcast a colleague, Neal, told me he'd switched all his radiators to thermostatic valves and says they work a treat. He can regulate the temperature of each room much more easily and thereby reckons he saves a fair bit of energy.

So here's your ethical brainteaser for the week: should I change my valves?

The world of ethical living is not glamorous is it?