How much energy does a condensing boiler save? is it worth worrying about?

[bernardgreen]

Your claim is that a boiler cycling can be more efficient than a boiler modulating the burner to input heat into a building to match the building's heat demand. No one will take that seriously.

People who have information about how the efficiency of a modulating boiler varies over the range of modulation may be in a position to take it seriously.

 

[hard-work]

Zoning heating is probably the biggest gas/oil bill saver, meaning you are not heating unoccupied spaces saving a lot. I know some who have dropped their gas bills 30% by doing that. The bigger the house, the more the saving. A multi zone system with rad valves on each rad means that independent temp control is in each room. A great advantage in comfort conditions. Having one central room stat can be a hindrance. To get rad valves in each room means you have to design the system to suite. A LLH and smart pumps on space heating zones can give that. To ensure efficiency, weather compensation can be used ensuring the flow temp is as low as possible. Using a combi, there is no problem. Heating a cylinder, it is best to use a DHW priority system. To do this you have to kid the weather compensator, so it thinks it is well below freezing outside to ramp the boiler temperature right up, to reheat the cylinder quickly. A simple relay can do that by using a simple cheap relay - an old trick in commercial control systems - a fully open or closed outside temp circuit will send the boiler temp either one way or the other, that is full on or off. I do believe Intergas have no problems with it. Doing it gives a twin temperature boiler using a simple cheap relay - well one temp mode with maximum temp and the other variable to the outside temperature.

Even our ex obnoxious Intergas man states that:
https://www.diynot.com/diy/threads/controling-vented-cylinder-and-a-combi.363109/

Look at at page 24. Cylinder sat wired into boiler as is the diverter valve. Weather compensation on CH then ramps up top max boiler temp when the cylinder calls for heat. Boiler switches activates the diverter valve.
https://intergasheating.co.uk/wp-co...-Compact-HRE-Installation-manual-88287805.pdf

On multi heating zones, probably external control is the way to go.

 

[hard-work]

People who have information about how the efficiency of a modulating boiler varies over the range of modulation may be in a position to take it seriously.

Bernard you are right in that the burner efficiency can vary along its modulation range. But I emphasise over a heating season. Manufactures have gone to great lengths over the past few decades to eliminate boiler cycling. Saying a boiler modulates down to very low kW is a selling point. The latest Intergas boilers modulate down to around 3.5kW, as they proudly boast in their literature. Which is around 10:1 modulation. Others boast 10:1, and I do believe Vokera amongst them, Vulcan's paymasters.

 

[hard-work]

Many makers have come up with more sophisticated thermostats as Eric in post 1 notes:

Honeywell Y6630D thermostat that had built in anti hysteresis software which started to cycle the boiler off/on as it approached the target temperature which to be fair worked very well, however not so sure if it saved any money by not over shooting, as each time boiler switched on it was at max output,
​

Using close boiler cycling to maintain a setpoint. Even he has reservations about it.

 

[ericmark]

Oh yes and I have work with Siemens HVAC control, but can't for the life of me work out what 3.3 kV, 10 kV or 11 kV voltage has to do with a domestic boiler? If you mean Heating, ventilation, and air conditioning then say that, not a set of letter which because I know Honeywell don't use high voltage I realised did not mean high voltage alternating current, but some thing else.

I know Myson do manufacturer fan assisted radiators to heat and cool with single or double matrix, but heat pumps and air conditioning units don't with most domestic installations run using a condensing boiler to do heating. I always felt air conditioning includes pollen removal and humidity control, not simply cooling, but also a boiler should boil the water, and where I work they do, in some cases producing super heated steam, I think with domestic a boiler that actually did what its name says would be considered faulty!

I will admit I don't tend to say residual current device I call then RCD unless on a boating forum where I know RCD means recreational craft directive, so tend to use the old names ELCB-c or RCCD, unless the tread starter refers to FCU first time I try to say fuse connection unit (FCU) the same with thermostatic radiator valve (TRV) I hate jargon, and this a bulb grows in the garden thing really winds me up, OK may be today a bulb is not bulbous, and a transformer does not transform (look at any bathroom toothbrush outlet) and it is no water in a car radiator it is coolant, I think it is still coolant in a central heating radiator as mixture of water and inhibitors?

But at work we have a water tower, even if it does have treated water in it, often it is more water than the stuff out of the taps, treatment is to remove impurities not add them. Makes the fire tube boiler last longer. Not sure I would want to catch the latent heat from the gases, I know my dad worked in a coke oven and they were very dangerous places, don't want creosote dripping off the smoke stack.

This is not the boiler I have at home it was just a bit of fun when the government said we should try to work from home. Yes Joan is an old boiler (not my wife's name) I look forward to getting back to normal, the thread has been useful, I had intended to sell old house, but now it seems my son it taking it over and selling his, and really it needs the two boilers combining into one new efficient boiler, there were a lot of errors in the installation, I miscalculated how much heat would go up-stairs, added a couple of radiators down stairs latter, never fitted one on landing, did not fit pressure release valve or by-pass valve, and the fitting of UPVC doors front and back has reduced draft so less heat needed down stairs, it used 8mm and 10mm micro bore pipes which worked well, but not so sure how good when the flow rate is reduced?

It will be his house, so I can suggest, and likely pay towards the up-grade, I followed his advice and fitted Nest, but by time I fitted it Google had bought it out, so all the cleaver ideas of linked TRV heads went out of the window, but the problem is all these systems tend to interlink, so if you have Nest speakers, Nest door bell, Nest smoke alarms there is some sense staying with Nest, even if not the best wall thermostat.

So much depends what he is bringing with him from old house. And from what has been said here on this tread, I don't think the gains from OpenTherm are high enough to worry about, think the biggest saving for heating will be to replace the tin integral garage door for some thing that stops the garage getting cold, as loads of insulation in outside walls, but inertia walls and ceiling is very poor.

 

[bernardgreen]

and I do believe Vokera amongst them, Vulcan's paymasters.

Who is the "paymaster" who encourages you to make rude comments about people posting on this forum.

Factual adverse comments about equipment are acceptable, even welcome ( if true ) but rude comments about people are never acceptable on any forum. ( and no I am NOT a moderator on this forum )

 

[bernardgreen]

But I emphasise over a heating season.

Is that a way to avoid discussing the true efficiency of the boiler when operating at its lowest heat output setting.

 

[vulcancontinental]

Who is the "paymaster" who encourages you to make rude comments about people posting on this forum.

Factual adverse comments about equipment are acceptable, even welcome ( if true ) but rude comments about people are never acceptable on any forum. ( and no I am NOT a moderator on this forum )

I work for a boiler company but don't feel any need to name drop, don't try to sell anything, don't need to promote any particular product, justify anything or mention what I've done in the past. Other people do.

 

[hard-work]

Is that a way to avoid discussing the true efficiency of the boiler when operating at its lowest heat output setting.

Unless the makers give the detailed facts, which they do not, well not willingly, knowing the efficiency of a continually modulating burner over its range is difficult to pin down.

 

[ericmark]

Is that a way to avoid discussing the true efficiency of the boiler when operating at its lowest heat output setting.

I think this is one of the big questions, at least for me, if there is a graph showing boiler efficiency then it would need three inputs not two which means it is hard to display, boiler output, and the ∆T which if I am understanding is difference between output and input temperatures and also the input (return) temperature.

All very cleaver stuff, but all it needs is some one to feel cold and open the lock shield valve and all this careful setting is up the creak. I have again and again gone to a home, to find every lock shield valve wide open, as to who opened them all, hard to say, however I know with my dad's house the central heating installer had left them all wide open.

Now the wall thermostat is easy for the house holder to understand, be it °F or °C we all understand what they mean, so be it 68°F or 20°C they know that is a comfortable temperature, but we are told * to 4 is 6°C to 22°C with 5 being wide open, but hang on my old TRV heads marked off l to llll and * to 6 so it seems every head has it's own scale. OK now my heads so °C but most people still have some number system with no idea what they mean.

On first fitting electronic heads I realised an error, they were fitted on the return, so by time the TRV got warm, the radiator was stinking hot, so the room over shot the mark, careful adjustment of the lock shield valve so the radiator heated up slower, cured the problem, and then the room actually reached the temperature set, on deciding to sell the house the electronic heads were removed, and old wax or liquid heads put back, set to between 3 and 4 I found they were quite good really at controlling the temperature, as now the lock shield was set correctly, other than not programmable nothing wrong with the old heads, the problem is with * to 6 and zero to 4 turns on lock shield you have two variables so near impossible to know which is wrong.

Dads central heating fitted over the summer, sensible time to do it, but then turning on central heating and setting lock shield so there is 25°C temperature drop across each radiator when it is 28°C outside, I can understand why not set. And I had been told 15°C at 25°C likely the home owner will say "this radiator is not getting as hot as it should" and will likely adjust the finely tuned settings, @hard-work comment about TRV with the lock shield built in so user does not even know it is there makes a lot of sense. In fact everything @hard-work says seems to make sense once thought about, specially the 25°C drop across the radiators, and if the house has had cavity wall insulation, double glazing, loft insulation, new front doors all reducing heat loss (which is true for my old house) and before this was all done I needed a 24 kW boiler, then once all done yes a 12 kW should be ample, and all radiators will be over sized with old methods as designed to liberate 24 kW now only needs to liberate 12 kW so OK doubling temperature drop across radiator not a problem.

But then we try turning off unused rooms as well, so that 12 kW is now only heating half the rooms, but losses in those rooms is increased, insulation house to outside it good, but room to room is not, so radiators still end up under size. Early on @vulcancontinental listed the savings having a boiler work efficient, in pence per £5 spent, he also said

Remember you're dealing with people who with a straight face can show you certified figures for their products of 108% and 127% efficiency while the appliance case is warm, the flue is warm and there is a plume at the terminal or where one brand will claim a flue to return water temperature differential of 5 degrees and another of 7 degrees yet both have the same space heating efficiency figures.

I understand how you can have 120% Octant rating, Septant and Octant are used to calibrate an engine, but perpetual motion is still not possible, so 127% efficiency can't be done so I wonder how much can be really be saved, likely the lights with LED 20W LED tube to replace fluorescent says equivalent wattage 100W, so a 58W fluorescent even with magnet ballast was over 5400 lumen so 100 Watt is around the 10,000 lumen mark but this tube with equivalent wattage of 100W is only 2000 lumen it is really around equivalent wattage 24W, it does not say equivalent to tungsten, nor should it as it replaces a fluorescent, I look at the claims and think any one who believes them must be daft, however we have an advertising standards agency who should pick it up when clearly wrong, Mars bars had to remove help work rest and play, and that shampoo had to remove claims what caffeine can do for hair growth, but some do seem to get away with it, whiter than white, how could that ever happen?

 

[JohnD]

If we look at the original question in the heading

How much energy does a condensing boiler save? is it worth worrying about?

Then I have accurate experimental results, of gas usage for the final 46 months of my old iron boiler, and the first 46 months of my replacement condensing boiler.

Same house, same location, same occupancy, same insulation, same radiators, four years average of warm and cold winters.

So I can give one real world answer.

Sadly it is not based on fanciful imaginings and theoretical calculations so does not fit well into this thread.

Yours may, of course, vary.



old boiler 46 months usage 6493 cu.m
new boiler 46 months usage 4449 cu.m

2044 cu.m is about 23,500 kWh
current price about 3p per kWh for gas
saving 23500 x 3p = about £700 edit - corrected - over 46 months - so about £170 p.a.

Both periods started and ended in summer when gas usage is negligible.

So my answer to the question "is it worth worrying about" is "yes."

But of course I didn't change it until my old boiler was beyond repair.

The new one is a conventional, not a combi. Same as the old one.

I have seen the published SEDBUK efficiency ratings but to me the actual figures are much more important.

 

[ericmark]

Unless the makers give the detailed facts, which they do not, well not willingly, knowing the efficiency of a continually modulating burner over its range is difficult to pin down.

You posted as I was writing that is very true.

 

[ericmark]

I see your point @JohnD but I was talking about same boiler, it is clear a 1980's boiler replaced with new will jump 75% to 90% plus so real saving. But that 90% plus run flat out on/off or mark/space regulated, to run efficiently modulated is the real question. Same boil but different controls.

Maybe my English was not plain, remember the signs "Beware of the man eating Haggis"?

Maybe I should have said when it is condensing.

 

[vulcancontinental]

If we look at the original question in the heading



Then I have accurate experimental results, of gas usage for the final 46 months of my old iron boiler, and the first 46 months of my replacement condensing boiler.

Same house, same location, same occupancy, same insulation, same radiators, four years average of warm and cold winters.

So I can give one real world answer.

Sadly it is not based on fanciful imaginings and theoretical calculations so does not fit well into this thread.

Yours may, of course, vary.



old boiler 46 months usage 6493 cu.m
new boiler 46 months usage 4449 cu.m

2044 cu.m is about 23,500 kWh
current price about 3p per kWh for gas
saving 23500 x 3p = about £700 p.a.

Both periods started and ended in summer when gas usage is negligible.

So my answer to the question "is it worth worrying about" is "yes."

But of course I didn't change it until my old boiler was beyond repair.

The new one is a conventional, not a combi. Same as the old one.

I have seen the published SEDBUK efficiency ratings but to me the actual figures are much more important.

I think the price per KW is higher than you mention plus the £700 saving would be spread over 46 months would it not rather than per annum?

 

[JohnD]

I think the price per KW is higher than you mention plus the £700 saving would be spread over 46 months would it not rather than per annum?

1) no

from my recent bill

2973.15kWh at 2.973p per kWh £88.39
1 Feb 2020 - 1 Feb 2020 10159 - you gave us your meter reading

2) quite right.
not such a big saving as I thought.
have corrected above