Boiler sizing from cubic area, or actual usage

[fixitflav]

There is a guy called Jeff Howell who I think writes in the Daily Telegraph, who argues that leaving the heating on at the lowest setting saves money. His argument is that when a room cools water vapour condenses in the fabric of the building, the walls etc. When you then heat the room back up it takes additional energy to convert that water back into vapour. Every time you heat and cool the house this process repeats. He also makes a separate argument that the cooling of the house and condensation, and the damage it does to window sills and other components, outweighs any energy savings.

This is of course the opposite to the conventional argument made by the energy saving trust and just about every other related body, that leaving the heat on costs more. I think that both are right and both are wrong, depending on the circumstances. I suspect that for people who are in the house most of the day it makes sense just to leave it on, rather than let it cool for a few hours while you are out and have to ramp the heat up to get it comfortable again, but for people who are only getting back to the house from say 6pm I doubt it. The greater the difference between inside and outside temp the greater the heat loss, so I can't see how for people who are away for 8 hours plus each day, it can make sense to leave the heat on. I suspect many of Jeff Howells readers are pensioners, which is probably why it works for his audience who are only popping out for the bingo for a couple of hours...

I've always turned it off when its not being used and I plan to get a remote operated stat regardless of whether I replace the boiler. When I'm away in winter I'd prefer to leave the heating off, but with the option of being able to get it fired up a few hours before I get back.

Thanks for that. No doubt different "experts" have different opinions. I agree with the guy that minimising temperature cycling is a good thing. As I said, if the walls, furniture etc are cold, need the stat higher for the same comfort, but whether that uses more or less gas overall I wouldn't like to say.
If you're away in winter I trust you have a frost-stat, or leave the heating on low (specially in Scotland ).

 

[Kaymo]

I think it would be pretty hard to prove conclusively one way or another, but if you take the argument to extreme, i.e. someone who is away for 5 days a week and back only at the weekend, there is no way Howell is right. If someone is in the house a good portion of each day then maybe. I think the argument about condensation is an interesting one though, how many households have spent more on fixing dampness problems due to condensation, than it would have cost to keep the heating on.

I don't have a frost stat as far as I am aware in the current set up. Would be looking at that if I replace. I do always turn the water mains off before I leave, but to be honest it has to be really cold outside for inside pipes to freeze and it wasn't really cold enough any time we have been away so far in this house. During the big freeze of 2010/11 in previous house an under floor pipe froze overnight coming into Boxing day when we were in the house, no leak though, just no water in the kitchen and when I crawled underneath a 3 inch split in the copper pipe and a lump of ice poking out of it. Luckily I had a section of pipe and fittings in the garage. -18 outside that winter where we were.

 

[fixitflav]

I think it would be pretty hard to prove conclusively one way or another, but if you take the argument to extreme, i.e. someone who is away for 5 days a week and back only at the weekend, there is no way Howell is right. If someone is in the house a good portion of each day then maybe. I think the argument about condensation is an interesting one though, how many households have spent more on fixing dampness problems due to condensation, than it would have cost to keep the heating on.

I don't have a frost stat as far as I am aware in the current set up. Would be looking at that if I replace. I do always turn the water mains off before I leave, but to be honest it has to be really cold outside for inside pipes to freeze and it wasn't really cold enough any time we have been away so far in this house. During the big freeze of 2010/11 in previous house an under floor pipe froze overnight coming into Boxing day when we were in the house, no leak though, just no water in the kitchen and when I crawled underneath a 3 inch split in the copper pipe and a lump of ice poking out of it. Luckily I had a section of pipe and fittings in the garage. -18 outside that winter where we were.

Valid points. I had a pipe freeze in 2010/11 but I wasn't as lucky, in Australia at the time and came back to some damage. A friend house-watching had turned the water off but not before a mess made. Since then I turn it off if away in winter for any length of time, then at least it's limited to a storage tankful. And I leave the stat on 10°C (no frost-stat).