Energy myth-busting: Is it cheaper to have heating on all day?

JayBee34

Bear in mind that a domestic boiler or combi system is not 100% efficient--the exhaust gas contains heat that you are paying for. Electricity unit cost is higher because the generators and distributors take the losses from using fossil fuels and are likely to be more efficient on the scale they work at. In particular, an immersion heater transfers all the metered kW to the water. However, it's years since I worked in the energy conservation consultancy field, so someone else will have to put in the actual efficiency figures for typical domestic boilers and the power generators.

FTW25

Just run a couple of checks on a very recent cold day.


Boiler on from 'cold' for exactly one hour with all the house panel radiators on (*) Cost including 1 hour of the daily standing charge close to 30p. (* all got hot: one or two _may_ have been cut off by the thermostatic valves before the hour was up, although all rooms other than the lounge were otherwise unheated and struck on entry as pretty chilly.


Boiler off and went to pub for ca. three hours to let house cool. (Although maybe not right down to outside ambient, with double glazing, cavity insulation, and reflector panels behind all radiators.)


Back home, house certainly cooled off.


Gas fire (old style, with three panels and 'open' flame jets) in lounge/living room then on for same time. Room soon got very comfortably warm: would have reduced to 'low' = one panel lit if not on test. Cost per hour 10p including standing charge.


So aim to use one heated room as far as possible. Set boiler control to fire it up for one hour half an hour before you get up (...to take the edge off the house and top up the hot water tank). Use the gas fire as required during the day. , Boiler on again for two hours in the mid evening to warm the bedroom(s) and make hot water for shower(s)/bath(s). Electric blanket _was_ on via timer for one hour. (Memo to self: must check what THAT costs..) Night, night; sleep warm and well.

angelta

I have combi boiler, about 12 years old. Room temps are controlled via the radiator thermostats. No room stats. Both the user manual and my plumber tell me the boiler should run on full with the radiators turned to the temperature desired.
Is this correct? I can never bring myself to run the boiler on full, so it is usually running at 70 degs. Unless it is exceptionally cold, radiators are turned to 1, occasionally 2, but so far this winter the heating has been off more than it is on. Am I doing the right thing?

Cardew

angelta wrote: »

I have combi boiler, about 12 years old. Room temps are controlled via the radiator thermostats. No room stats. Both the user manual and my plumber tell me the boiler should run on full with the radiators turned to the temperature desired.
Is this correct? I can never bring myself to run the boiler on full, so it is usually running at 70 degs. Unless it is exceptionally cold, radiators are turned to 1, occasionally 2, but so far this winter the heating has been off more than it is on. Am I doing the right thing?

Firstly it depends in your boiler is a condensing boiler or non-condensing boiler.


If a non-condensing boiler, then for heating it doesn't matter (for economy reasons) if it is at maximum. Some people don't like it too hot if they have young toddlers as the radiators could burn.


With a condensing boiler, in principle the lower you have the water temperature, the better the economy; you want to keep the boiler in condensing mode as much as possible.


I am surprised with a 12 year old boiler you don't have a room stat. They have been mandatory for a long while - 25 years??


Not that I am a fan of fixed room stats.

r2015

I am surprised with a 12 year old boiler you don't have a room stat. They have been mandatory for a long while - 25 years??

That is not what I was told when I replaced my warm air heating with radiators earlier this year.

When I got my quote there was not a room stat quoted, I had to ask for one.

I was told that as long as all the radiators had thermostats a room stat was not essential.

Even the boiler manufacturer said that.

matelodave

The external room stat is there to turn the boiler & pump on and off when the heating demand is satisfied - it's not a perfect solution as it can only do it from the reference room. That's why the stat has to be in a room that is heated by the boiler and not controlled by a TRV - the hall is not usually the best place for it. Other room temperatures are controlled by TRVs.


Without a room stat the pump will run constantly and the boiler will try to stay hot all the time and hot water will be continuously circulated around the system. The room temperatures will be controlled by the TRVs but running the pump & boiler all the time will waste energy when it's not needed.


In some systems the pump is controlled by the boiler which kick's it on and off when the boiler cools - just to circulate some water to see if it needs to heat. Still not a very efficient way of controlling the heating.

Cardew

r2015 wrote: »

That is not what I was told when I replaced my warm air heating with radiators earlier this year.

When I got my quote there was not a room stat quoted, I had to ask for one.

I was told that as long as all the radiators had thermostats a room stat was not essential.

Even the boiler manufacturer said that.

I am not saying a room stat is essential(or IMO desirable) but it has been mandatory for years in new installations.


https://www.mybuilder.com/questions/v/5277/is-it-a-legal-requirement-to-have-a-room-themostat-fitted-with-a-new-boilerheating-system

molerat

I cannot find where Part L states a room stat must be fitted. The nearest quote is "should" and states possible alternative methods. Part L is, as would be expected, a bit vague on many things. It has lots of coulds and shoulds but very few musts.

orrery

Cardew wrote: »

Firstly it depends in your boiler is a condensing boiler or non-condensing boiler....With a condensing boiler, in principle the lower you have the water temperature, the better the economy; you want to keep the boiler in condensing mode as much as possible.

This may be one of those "In theory, Theory and Practice are the same, but in practice they are different" situations.

Since I've had the Tado intelligent thermostat system I've been able to see the history of when the boiler is being turned on and monitor its performance. Once the initial continuous heating period is over (i.e. getting the rooms up to the target temperature) then the boiler 'demand' uses proportional control - short bursts of heating with gaps between, with the periods of heating on/off varied to maintain the correct temperature. Once in this mode, the short heating bursts seldom cause the water temperature to reach maximum (68C as set at the boiler) - typically it only ever gets to 60C, with the return temperature only rising to about 40C before the demand cuts off.

Thus, it is likely that a high boiler temperature will reach the target earlier and then enter proportional control, and very efficient running, earlier.

If the thermostat wasn't managing this process then the TRVs would be almost closed down, the flow rate very limited, the boiler temperature would be continuously very high (the boiler allows +5C over the maximum set before it cuts out) and the return temperature very high - typically between 55C and 65C) which must make a condensing boiler very inefficient.

I'd say, even with TRVs a room-stat is an absolute necessity to give rapid heating and efficient operation.

malc_b

orrery wrote: »

Thus, it is likely that a high boiler temperature will reach the target earlier and then enter proportional control, and very efficient running, earlier.

That seems dubious. Are you in effect saying that it would use less petrol in a car to go really fast and then coast?

If you look it the other way round you need to feed a certain amount of energy into the house. That's a fixed amount for a particular time and day. If you do it inefficiently then you use more gas, even if you then go on to enter efficient mode. I'd agree that taking longer to warm the house up increases the loss slightly but not by the same as running inefficiently.