What temp should my house be at?

[forthelifeofpomme]

My lodgers keep bumping the temp up and have their radiators on full in their room. They want to sit around in t-shirts and use a summer duvet, I wear full pyjamas and have two thick duvets. I grew up without central heating so I know I probably in the minority here! I pay all the bills - what is a decent temp for us to agree to?

We use calor gas for our central heating as we are in the countryside. Heat downstairs in Autumn is provided by the log fire in the evenings and a convector heater in the mornings.
We have warm duvets and hot water bottles for the bedrooms. Having a shower is a bit torturous until inside the shower.
On a cool night it can be as low as 14c upstairs and downstairs is usually 21c once the fire has been going for a few hours.
But as I'm the fool who gets up at 6am, I have to shiver in my jumper whilst the convector heater takes the chill off and gets up to at least 18c for the morning.
We never have heating on at night. Not even in the coldest Winter.

Somewhere in the range 18-21 IMO. And I wear T-shirts and use the same duvet all year round. Though in our house we can never really get everywhere the right temperature, the bathroom's got no roof insulation and is always the coldest room.