Keeping the boiler on all the times saves gas?

[Nigel Watts]

I recently had a fascinating chat with the plumber who was flushing out my heating system.

He told me that the way to keep the gas bill down in the winter was to keep the central heating and hot water systems on 24 hours a day with both the boiler and house thermostats turned up high, with each room regulated by the thermostatic valves on the radiators.

His argument was that gas boilers are at their least efficient when taking the circulating water from cold to hot and that one should instead ensure that the circulating water is constantly kept hot, with the boiler only switching on to top it up.

Despite learning about thermodynamics at University, I can't quite see this. The overall heat loss from the non-boiler part of the system will clearly be greater if the system is kept constantly hot, and why should the boiler be any less efficient when taking the temperature up from hot to very hot than it is when taking it from cold to hot?

Before you ask, no the plumber was not from British Gas.

 

[88v8]

Condensing boilers only condense at high temperatures, so are less efficient during run-up.

And, if one runs a boiler only for a short time, in the morning say, then it will expend a lot of energy in heating up the system with no time for the heat to percolate the house. Arguably a complete waste.

Otherwise I see no merit in his assertion.

And as to relying on radiator stats to control temp, unless one also has a thermometer in each room so one can keep an eye on the actual temperature instead of just judging it by perception, rad stats can be an excellent way to waste heat.

V8

 

[Flyfisher]

Despite learning about thermodynamics at University, I can't quite see this. The overall heat loss from the non-boiler part of the system will clearly be greater if the system is kept constantly hot, and why should the boiler be any less efficient when taking the temperature up from hot to very hot than it is when taking it from cold to hot?

I can't see it either. Raising the temperature of a certain volume of water by a certain number of degrees requires a certain amount of energy, regardless of its starting temperature.

I've read that condensing boilers can take a while to get into 'condensing mode', so short-cycling them can mean that they don't run at their most efficient level , but thats nothing fundamentally to do with the temperature of the water (though perhaps just keeping hot water 'topped up' by constant short bursts might actually be LESS efficient than a long burst of heating from cold?).

This whole 'energy efficiency' thing is a can of worms though. Anyone care to work out the embedded energy in a boiler condenser that becomes corroded and has to be replaced a number of times during the life of the main boiler? Or the energy involved in replacing that old but perfectly serviceable non-condensing boiler just because it is a bit more 'efficient'.

I suspect that, for most people, heating efficiency all boils down to how much money they have to spend to feel comfortably warm. In that respect, a pair of long-johns and a woolly jumper is probably the most cost-effective contribution towards home heating 'efficiency'.

 

[Lindyboo]

I’d say he’s right. In an impoverished former life I used to have the gas boiler (not combi or condensing) on timer for mornings and evenings in an attempt to save money. It would take well over an hour for the house to reach suitable temperature and then be stone cold again within an hour or so after switching off. If the house was occupied outside these times (weekends) then it was either freeze or have the heating on and fret about the cost.

Heating engineer told me the same thing – keep it going all the time – so I started to turn down the thermo to a low setting at night and turn it up to comfy when getting up or coming home. House would be warm in ten minutes. I did careful timings and calculations of how much gas was being used and found that the boiler was firing up for only ten more minutes per day when on constant than it was when it was on twice a day. The house – and I – were never cold thereafter and the extra on my gas bill was negligible. I know several other people who do the same thing and have had the same satisfactory result.

 

[Keith Bowman]

Presumably the same theory applies whether the boiler uses gas, oil or dried camel dung?

 

[Lindyboo]

Yes, I would say so. Not using dung, though it seems to apply to our oil combi-condenser. I suppose the principle is the same, in that a boiler has to use a lot of fuel to heat a house from stone cold twice a day, compared to keeping it ticking over from warm.

We tested the idea when we first came here by keeping the settings on the boiler as the previous bods had them - i.e., on/off thrice a day, compared to keeping it going 24/7 and just turning the heat up or down as occupancy demanded. Still works out good for consumption and we have a warm house all the time.

 

[JoceAndChris]

Can't see how this would work here when all the heat is just getting lost all the time?

 

[Lindyboo]

Can't see how this would work here when all the heat is just getting lost all the time?

How do you mean 'getting lost'?

 

[plasticpigeon]

I've heard this many times, and it doesn't make sense to me.

 

[Flyfisher]

Against the proposition:

http://www.moneysavingexpert.com/utilities/energy-saving-myths
http://www.uswitch.com/energy-saving/guides/heating-on-all-the-time/

For the proposition:

http://www.telegraph.co.uk/property/propertyadvice/9831697/Jeff-Howell-can-keeping-the-heating-on-low-all-day-reduce-costs.html
(Interesting point about increased thermal conduction in cold walls)

Anyone care to run a controlled experiment?

 

[Baron de Gynes]

Gladly! Anyone want to pay for my next oil delivery, just in case?

 

[Flyfisher]

Think of it as an investment towards future savings once you know the true answer. :wink:

 

[mattice]

I guess it depends on the house, but I did some simple experiments in the winter as I moved the house from one big zone where the thermostat was in the coldest room (always on), with TPV's in every room, to a zoned regulated system with wireless valves. The results are in this thread: http://www.periodproperty.co.uk/forum/viewtopic.php?f=1&t=13780

I certainly won't be returning to always on! Very topical... heating on for the first time tonight :?

 

[Flyfisher]

Regardless of the always on/always off question, I'm already sold on a zoned heating system.

 

[jocelyn plummer]

A can of worms indeed! In all 3 of our houses, both my own Heating Engineer, (Gas Safe & all that) as installer, and Heat Team who service our Combi boiler, advise 24/7, radiator stats set to whatever temperature we require. At the moment we have the stats down to no.2 in every room, excepting the bathroom which has an old style cast iron radiator (inherited from previous owner) with a valve which is either on or off, so it is always piping hot when turned on.I have put stats onto the other 2 cast iron rads because the heat was too aggressive for the furniture in the rooms. With the fairly reasonable weather at the moment the radiators are barely warm, so they are not making excessive demands on the boiler to fire up. The house is warm.

I notice that somebody has commented that zoned heating regulation is a good way forward. I did this at Wisteria, zone 1 was downstairs and zone 2 was upstairs. each zone functioned efficiently to my requirements and it worked very well. Of course I was fortunate enough to install the heating system from scratch as we were renovating. It has not been possible to zone it here unless I start over.

Interestingly we have kept all our heating and lighting bills since 1993, as the number of radiators and rooms has been much the same from one house to another, we see very little change in the recorded units consumed-------------- so our usage is steady and as economical as we can make it. The oil boiler in North Norfolk was the greedy one!!

All one can do is be sensible and comfortable, extra jumpers etc and all the rest of it, the costs will continue to rise and our carbon footprint will be much the same.

Incidentally a friend of mine has just replaced his old boiler in the kitchen-- he was told that he had to remove the enclosing cupboard as boilers now have to be in open space-- have I missed a change in building regs?

 

[JoceAndChris]

Can't see how this would work here when all the heat is just getting lost all the time?

How do you mean 'getting lost'?

Glass porch very open to the elements, with huge gaps around all the doors and 18 large windows, huge gaps between bare floorboards suspended over earth, downstairs partially sunk into the earth, flags on earth, 5 open fireplaces and chimneys, cat flaps always taped open because Horry can't manage them, loft not yet insulated because Chris hasn't got round to doing all the wiring yet - no point even putting the heating on!

We never get any condensation or damp though

 

[tobydog]

Incidentally a friend of mine has just replaced his old boiler in the kitchen-- he was told that he had to remove the enclosing cupboard as boilers now have to be in open space-- have I missed a change in building regs?

Our new oil boiler (washing machine size) was fitted 3 years ago and sits in a utility space with the washing machine and there is no room for anything else. You can't actually walk into the space. Does this count as too small?

Regardless of the always on/always off question, I'm already sold on a zoned heating system.

I had a brand new house in 2006 with zoned heating. There was a thermostat in the hall and the other unit was directly above on the small landing. The problem was that heat from downstairs rose to the landing and kept triggering the upstairs unit to turn off. I had to set the temperature range somewhat higher so it continued to heat the bedrooms, one of which was 25ft long with an en-suite at the end (regularly cold). Had I stayed there longer I would have moved the unit into this bedroom to control the upstairs temperature. Given how large your house is FF, have a good think as to where you position your thermostats.

 

[wobs]

This whole 'energy efficiency' thing is a can of worms though. Anyone care to work out the embedded energy in a boiler condenser that becomes corroded and has to be replaced a number of times during the life of the main boiler? Or the energy involved in replacing that old but perfectly serviceable non-condensing boiler just because it is a bit more 'efficient'.

I suspect that, for most people, heating efficiency all boils down to how much money they have to spend to feel comfortably warm. In that respect, a pair of long-johns and a woolly jumper is probably the most cost-effective contribution towards home heating 'efficiency'.

Indeed. And of course, there is nothing alturistic about improving energy efficiency, even ignoring the imbedded energy of installing kit. Jevons paradox takes care of any carbon we have saved, to ensure that our energy consumption will go up, as society becomes more efficient. Its only worth it if we save money.

As to the original question, my own theory is that it depends, but this is only a guess.

Surely it depends on factors such as the amount of time it is on/off, and the amount of heat loss the house has. Eg. if you're in a high heat loss house (I'm sure many here are), then it may be cheaper to have it on for just a few hours per day, as you are not pumping all that heat into the outside air. It may take a while to get up to temperature, but if your heat loss is sufficient, it may use more energy to have it on all the time.

Another factor is the relative temperature. If you want it 10C hotter inside than out, then you will be constantly burning more fuel than if you wanted it 5C hotter. And at night (when in bed), when the outside temperature is lower, and one usually has the heating off, the boiler would be working particualrly hard if it was on 24/7.

My own theory is that if you had a very thermally efficient house, it might be worth having it on 24/7 under certain circumstances.

Some articles here:
http://www.uswitch.com/energy-saving/guides/heating-on-all-the-time/
http://www.moneysavingexpert.com/utilities/energy-saving-myths

If anyone has any decent evidence for either way, it would intersting.

 

[agbagb]

What a can of unsubstantiated worms this question opens up! You would have thought there will have been loads of studies with hard scientific evidence to give some answers. But it seems not.

What I do know is that modern condensing boilers work in the efficient condensing mode only when the return hot water temperature is low (55 degrees ish). Boilers now modulate their burner output to try and maintain this BUT they can only go down so low. If the radiators don’t shed the heat the return temperature will be too high for condensing to occur.

This has implications on the discussion. Starting from cold, the boiler will be efficient until the water temperature has risen. Then if the CH water temperature is set high the radiators may not lose enough heat even when rooms are still cold. Some rooms might have warmed up and the thermostatic valves have switched the radiator off. So the Hot Water Return is too high for condensing.

By having the heating on constantly (with a low CH water temperature) controlled by a room thermostat may prevent the above as the boiler fires for shorter periods after the radiators have cooled sufficiently. But if most radiators have thermostatic valves and many are off it wouldn’t be much better.
There are so many factors to consider it’s worth playing around with and experimenting. The trick is to balance the system so when the boiler is firing it is always condensing.

Aside from the other factors, like damper walls conducting more heat and big swings in internal temperatures playing around with relative humidity, it should be cheaper to run the heating just when you need it if it’s balanced right. But don’t let the temperature drop too far in the off time.

My preferred option is for a timed room stat and radiator flows balanced so all rooms get to the desired temperatures at the same time. So in effect the heating system is on all the time maintaining a minimum room temperature of 14 degrees and boosting to 18 degrees in the morning and evenings.

Having said all that YES closing the back door, lighting a fire and putting a jumper on makes a bigger difference.

 

[Nigel Watts]

Very interesting thread, especially about condensing boilers needing a sufficiently cool return flow to allow the steam in the waste gas to condense in the secondary heat exchanger (this I do understand from my thermodynamics course back in 1978).

My boiler is an oldish (c. 2003) Potterton Suprima, which is non-condensing. Although quite cute and compact, they suffer from dodgy circuit boards. I am now on my third board, and the last time it went wrong I concluded, probably incorrectly in retrospect, that my system needed flushing out. An £800 flush of my 22 radiators+underfloor circuits produced a disappointingly small quantity of gunk.

The next question, I suppose, is at what point does it make sense to replace the boiler with a condensing one?