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

[vulcancontinental]

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.

Do you have a plume at the terminal? If so you are not harvesting all the latent heat. The latent heat amounts to 0.93KW/cu m and the EU reckons you're lucky to get around 0.4kw of that if your return is 41 degrees.

Controls may modulate the boiler flow and of course return which if low enough provides the opportunity for condensation on the exchanger surface but this only happens if enough sensible heat has been removed first. e.g the return enters the boiler at 40 but one exchanger may have 2% of it's surface at that low temperature a better exchanger 5%.

 

[vulcancontinental]

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.

That's a good price

 

[hard-work]

Non-condensing boilers are designed not to condense.

You posted as I was writing that is very true.

Non-condensing boilers are designed not to condense. The heat exchangers are smaller. Also the system and radiators are designed to keep the boiler temperatures high to prevent boiler condensing. Hence the 80C flow and 69C return which must be maintained to keep the return temperature above the dew point. As the articled states, many radiators, etc are still sized on this 80-69 (11C delta T). When a house is up to temperature, the radiators are oversized.

The copper finned tubed heat exchanges could be run on lower condensing temperatures. Any condensate that was produced would immediately be turned to steam - hence why on some non-condensers you get constant drips out of the flue - the flue is supposed to slant down, away from the boiler, while condensers do the opposite. I have never seen a copper finned heat exchanger boiler be affected by running at low temperatures, not one. I recall reading the instructions of a Microgenus combi (non-condensing) where it stated at a particular temperature you will get 92% efficiency. Knowing this a system can be designed around it then getting efficiencies of condensing boilers.

In a flat, or small two bed house, the difference between a condensing boiler and non-condensing, especially when installed by the average plumber, is minimal in fuel used, translated into pounds saved. As many have experienced when having a boiler change then looking at their bills. Incidentally Vokera, make an excellent non-condensing boiler. I believe the only one available.

 

[hard-work]

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

Did you compare sedbuk to your figures?

You are comparing the worse case scenario with the best case. The difference between a copper fin-tubed non-condensing boiler and a condensing boiler is not that great, and as I have mentioned in another post, if you design you system around a new non-condensing it can be very narrow between them.

 

[JohnD]

You are comparing the worse case scenario with the best case.

no, I'm comparing actual with actual.

Reduction in energy usage is of interest to me. What would I gain from looking at numbers in a table?

 

[hard-work]

no, I'm comparing actual with actual.
Reduction in energy usage is of interest to me. What would I gain from looking at numbers in a table?

You didn't get my point. The worse case scenario is an old cast-iron boiler. If your old boiler was a fin-tubed copper heat exchanger your savings over the year (substantial at £700) would be far, far less.

It depends on what the numbers in the table are. Sedbuk is based on a boiler hooked up to an average rad system, so it gives x percentage for the boiler - say it is 90%. Yet this 90% boiler when hooked up to a single use heating only a thermal store, can be fitted using a blending valve to ensure low return temperatures, will operate at far higher efficiency. Because it is working at the ideal hydraulic environment.

I gave this in this thread:

So, a guide:

1. Have weather compensation to ensure the flow temperature is as low as possible.
2. Have load compensation to give room temperature accuracy (superior comfort conditions) and near eliminate boiler cycling. And also keeping the flow temperature as low as possible. Opentherm, etc.
3. Have a balanced rad system. The Intergas shop article mentions the combined thermostat/flow IMI rad valves which have a the lockshield function (the flow) integrated. This is handy as it comes with a chart stating how to set the flow side.

The above three will ensure a condensing boiler works more efficiently for sure.

The article was pretty well right. But, some boilers can have load compensation and weather compensation operating together. The Ideal and Keston do (Ideal is a popular model). Yet few are wired up with OpenTherm room stats and outside weather compensation, even though weather compensation is in the boiler - few plumbers understand it all. If they were wired up, the efficiencies would rise for sure.

I never came across a non-condensing boiler that had load compensation. It could be hooked up by an outside controller of course. I recall one years ago that sensed the return temperature with an aim to keep the temperature low by switching the burner in and out. No longer on the market.

 

[JohnD]

You didn't get my point. The worse case scenario is an old cast-iron boiler. If your old boiler was a fin-tubed copper heat exchanger your savings over the year (substantial at £700) would be far, far less.

I don't care what the savings "would" or "might" have been for somebody else.

I'm surprised you haven't grasped that yet.

 

[JohnD]

You really, really don't want to understand that I don't care about your postulations.

 

[hard-work]

It is clear you haven't got much of a clue about what is being written. This thread is also not specifically about your particular case. You put this at the top of your post, How much energy does a condensing boiler save? is it worth worrying about?

In your case yes, in other cases no. It is clear you think it is worth spending a lot of money going over to a condensing boiler irrespective. Er, er, no. All cases are different. If you read and understood what is written you would have grasped that.

 

[JohnD]

ODFOD

you haven't even read my posts.

 

[JohnD]

Hooray!

 

[hard-work]

We await the result.

 

[ericmark]

The Myson fan assisted radiator control knob is broken, to adjust speed I have to switch off and remove cover and manually move the rheostat wiper, so my idea had been to fit a second thermostat below the Myson so full speed if under set temperature and ¼ speed if above, copying the idea of the new iVector having in may case three speeds off, ¼ and full, easy enough, but with a condensation boiler as the fan switches down or off, water flow remains unchanged. This would mean as the house warms up return water would get suddenly hot, so messing up any control using return water and making it unlikely return water would be cool enough. I had thought about a an activator like used on under floor heating to turn off flow when fan stops, but even they look ugly. And I was considering was it worth all the effort to try to use a 1979 Myson fan assisted radiator with a modern boiler, point is 1979 or not the output would need a huge radiator if not fan assisted.

 

[Hairymelon]

The phrase “get a life “ springs to mind

 

[dilalio]

Meanwhile, back in the real world... We have a doomsday virus to worry about!