Room Stat. Is it worth it?

[burnsey]

I've heard from a friend that it's cheaper to keep your boiler permanently turned on and to then control the room temperature with a room stat. Surely it can't be cheaper to have your house warm instead of cold when you're at work? I can't get my head around it although my moggies would appreciate it.

Can anyone confirm if this is true?

I don't have a room stat installed as of yet so I was looking at the honeywell cm921. The room stat itself is £80 to buy. Would this be a good setup?

 

[kevplumb]

I don't have a room stat installed as of yet so I was looking at the honeywell cm921. The room stat itself is £80 to buy. Would this be a good setup?

a geordie spenging £80 and not on beer

would be a goddam miracle

wouldnt be a bad idea you can set the temps to suit you sod the cats View media item 209

 

[JohnD]

1) Heating cost is driven by temperature difference (inside: outside) multiplied by time (the better insulated or smaller the house is, the lower the base figure will be). So the more hours you heat it for the more it will cost. Your friend is wrong. If you do not have a timer you are pouring money down the drain. Cats are provided with fur coats to enable them to cope with cool temperatures.

2) If you do not have a room stat you are pouring money down the drain. There is no need to spend £80 on a room stat unless you want to and have money to burn. A more expensive room stat will not be much better than a cheap one. IMO a wireless stat is more likely to go wrong than a £10 basic one. However you do need a timer as well (see point 1) so if you have no timer you can buy a room stat with its own timer if you want The sort of programmer/time you need depends whether you have a hot water cylinder or a combi boiler.

If you are fond of DIY plumbing you can fit thermostatic radiator valves as well (not instead) as a room stat, but if you have to pay someone else to do it after the radiators have already been fitted, it will cost hundreds of pounds and so the extra savings are probably not worthwhile. If they are fitted from new there is no extra labour cost in fitting then so they are a better bet.

If your heating system was installed without either a timer of a room stat then it was a very poor job and has been wasting money from day 1.

I am not a pro

 

[twgas]

Personally, I would go for a programmable room stat - these generally have about 4 time periods which you can set at different temps but do not turn heating off. for example, 20deg from 7am, 10deg from 9am, 21deg from 5pm and 10deg from 11pm, (then its back to 20deg next morning).
Depends on location as to whether a wireless or hard wired one is best.

 

[bengasman]

Installing a programmable roomstat, and using it effectively, can safe you a lot of money, quite possibly enough to pay for the outlay in less than one year.
I would go for the cmt 927 rather than the 921, or the siemens rev 24 which is even better.

A programmable roomstat is far superior to an old fashioned dial on the wall.
It gives you more flexibility, is 10 times more accurate, and as you can use different temperatures for different periods, there is no need to keep adjusting it (which most people forget as long as they don't feel cold) so it increases your comfort and saves more money.

I only use the rev 24 these days (I changed to this one but used the 927 before that) and all clients find it much better than the old system.
You do need to set it up properly, which a lot of people don't take the time for. When they are not set up properly, they are about as much use as a remote control without batteries.

As for the moggies, I have had cats most of my life, and found the majority like nothing better than a cardboard box, inside another cardboard box and an old cardy to line it. And for some reason, the smaller the box the better; they always choose the one that is only barely big enough for them.

 

[D_Hailsham]

1) Heating cost is driven by temperature difference (inside: outside) multiplied by time (the better insulated or smaller the house is, the lower the base figure will be). So the more hours you heat it for the more it will cost. Your friend is wrong.

It's not as simple as that. You have to take into account how quickly the house cools down and heats up. There will be a time where the amount of heat required to bring the house back up to temperature is exactly the same as the heat required to maintain a constant temperature while you are out. This all depends on the construction and insulation of the house.

 

[Legion]

Or failing that, turn on the heating when you are cold and leave it off when you are warm. Probably the best, cheapest way. Sorry if it sounds obvious.Not a vet but cats have a thick fur coat which probably does the job.

 

[bengasman]

...There will be a time where the amount of heat required to bring the house back up to temperature is exactly the same as the heat required to maintain a constant temperature while you are out....

That would require a situation where a 20 degree room looses no more energy per minute than a 18 degree room.
Heatloss is the product of differential and conductivity; lower either factor, and you lower the heatloss.
It really isn't rocket science.
Keeping the house warm is the same nonsense as people insisting that cars use less fuel at 60 than at 50 because the engine is more efficient at 60

 

[D_Hailsham]

...There will be a time where the amount of heat required to bring the house back up to temperature is exactly the same as the heat required to maintain a constant temperature while you are out....

That would require a situation where a 20 degree room loses no more energy per minute than a 18 degree room.

It's the rate of heat loss (and gain) which is important. Unfortunately, as Newton's Law of Cooling states, the rate of heat loss is not linear but exponential.

The same thing goes for heating up. Radiators, unlike electric fires, do not give out their maximum heat from the start, so it takes some time before the heat input exceeds the heat loss, which still obeys Newton's Law.

 

[kevplumb]

good point

the cooler it is the slower the heat loss makes sense

but then you have to heat the space again when you want to use it

so isn't it a bit swings and roundabouts until you find equilibrium

 

[D_Hailsham]

so isn't it a bit swings and roundabouts until you find equilibrium

Exactly the point I was making. For any given property, there will be a situation where the energy used bringing the house back up to temperature is the same as the energy used to maintain the temperature. If it takes more energy to reheat the room, then there is no point letting it cool down; and vice-versa.

 

[Legion]

so isn't it a bit swings and roundabouts until you find equilibrium

Exactly the point I was making. For any given property, there will be a situation where the energy used bringing the house back up to temperature is the same as the energy used to maintain the temperature. If it takes more energy to reheat the room, then there is no point letting it cool down; and vice-versa.

No, the gas used to keep the boiler on all day will cost more than turning it on to warm the house. when you come home at say, 5 0`clock. How hard is that to figure out? Why don`t we all leave our gas fires on minimim heat all day, that`ll save a fortune.

 

[JohnD]

there will be a situation where the energy used bringing the house back up to temperature is the same as the energy used to maintain the temperature.

no there won't

 

[imroberts]

Kevplumb

the cooler it is the slower the heat loss makes sense

The cooler it is , the faster the heat loss. Please explain to Hailsham. and yourself.

Theory states that the greater the difference in temperature between two areas, the greater the transfer of heat between them.

Take for example, an outside temperature of 10 degrees and an inside temperature of 12 degrees... your house will stay at the same temperature for a number of hours, even days... because the heat loss will be minimal.

If however your house is 30 degrees when it is 10 degrees outside... there will be loads of heat lost and you will have to keep reheating your house to prevent it from dropping rapidly down to 10 degrees.

 

[D_Hailsham]

No, the gas used to keep the boiler on all day will cost more than turning it on to warm the house. when you come home at say, 5 0`clock. How hard is that to figure out?

No there won't.

You are just making assumptions. It all depends on:

1. the outside temperature
2. the inside temperature when the heating goes
3. the rate of heat loss
4. the time between heat off and heat on
5. rate of heat gain

Kevplumb

the cooler it is the slower the heat loss makes sense

The cooler it is , the faster the heat loss. Please explain to Hailsham. and yourself.

I think Kevplumb was referring to the internal temperature, not the external. So in that sense he is correct.

It's the difference in temperature which determines the rate of loss of heat. If you turn the heat off and then plot a graph of internal temperature against time (assuming external temperature remains constant) you will get an exponential line.