Is 93% efficient any good for an oil boiler?

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Man's just been to do our annual service on our 20 year old Worcester Heatslave combi boiler. Gave it a clean bill of health and said it was running at "93% efficiency". That sounded prettty impressive to me, but is it? I was wondering what sort of efficiency I could expect from a new oil fired boiler these days?
 
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Sounds like rubbish to me...he's looking at combustion efficiency rather than overall performance
 
Yes, I wondered how he could possibly know that from the equipment he had with him (which just looked like a flue gas analyser). What would "combustion efficiency" mean, in layman's terms? Is that, for example, based on an assumption that 0% unburned hydrocarbons in the exhaust gas would mean 100% of the fuel was being burned, so that would be "100% efficient"? (leaving aside the issue of how much of that heat actually went into the radiators)?!
 
Yes, I think your understanding of "efficiency" is correct.
 
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efficiency is calulated on a log scale and makes bad boilers look better. for true efficiency find out your FGT and compare its to the fuels burning point.
 
If the engineer ran the boiler up to operating temp before analysis, then 93% is good. What is done with the heat produced is an entirely different matter. After servicing a boiler what else can an engineer be expected to report on?
 
Yes, I wondered how he could possibly know that from the equipment he had with him (which just looked like a flue gas analyser). What would "combustion efficiency" mean, in layman's terms? Is that, for example, based on an assumption that 0% unburned hydrocarbons in the exhaust gas would mean 100% of the fuel was being burned, so that would be "100% efficient"? (leaving aside the issue of how much of that heat actually went into the radiators)?!
Quite so. In reality, your boiler is probably about 75-85% efficient. Modern oil boilers are around 92-96% efficient. And in answer to your next question, no you shouldn't consider replacing yours unless it's broken beyond economic repair
 
If the engineer ran the boiler up to operating temp before analysis, then 93% is good. What is done with the heat produced is an entirely different matter. After servicing a boiler what else can an engineer be expected to report on?
I don't know really. I didn't watch him do it. It was just a throwaway comment he made as he left. He was here for the best part of an hour, vacuum cleaned some soot off the heat exchanger plates, replaced the nozzle and changed the flexible hose from the copper feed pipe to the pump. (That last bit annoyed me somewhat, as he hadn't asked beforehand and it had only been replaced a couple of years ago)!

Anyway, that aside, he gave it a clean bill of health (at that moment in time anyway)! I was just curious as to what the "efficiency" comment meant in real terms. He can't have run it for more than about 10 minutes though.
 
Yes, I wondered how he could possibly know that from the equipment he had with him (which just looked like a flue gas analyser). What would "combustion efficiency" mean, in layman's terms? Is that, for example, based on an assumption that 0% unburned hydrocarbons in the exhaust gas would mean 100% of the fuel was being burned, so that would be "100% efficient"? (leaving aside the issue of how much of that heat actually went into the radiators)?!
Quite so. In reality, your boiler is probably about 75-85% efficient. Modern oil boilers are around 92-96% efficient. And in answer to your next question, no you shouldn't consider replacing yours unless it's broken beyond economic repair
Excellent! - and yes, that WAS going to be my next question! From living with it for 20 years, it seems that they are quite simple creatures. So far, it has had one new pump, a couple of flexible delivery hoses, one fire valve, at least a dozen burner jets and a couple of fuel valve solenoids. Everyone says the controllers are the expensive bit. I guess that one day, the water jacket will rot through and that would write it off though? But getting back to the navel-gazing, in those figures you're quoting, is that the percentage of the energy available in the fuel from perfect combustion, relative to the amount of energy transferred to the water as it leaves the outlet of the boiler on its way to the radiators?
 
Hang on to yonder Heatslave as long as you can, Mr. A.....they are as tough and simple as they come. Parts are available (can't comment on the water jacket though) and repairs are DIYable right enough.
The only grumble I have with mine is when its on HW demand only......as soon as the hot tap is turned on, the burner prepares to fire up - but it goes through its 8 sec purge first. This usually means that the tap is back off again before then, and the burner has either just fired up or is about to before it is shut down again.
John :)
 
Thanks John. Yes ours does that. Also, if we've been away and we come back to a freezing cold house, it seems to want to heat the water BEFORE it starts chucking any heat into the radiators (even if we only advance the heating and leave the hot water off). On the whole though, it does a good job. A year or so ago, I got fed up having a couple of permanently cold radiators in rooms that we don't use much. (They're also rooms that happen to be furthest from the boiler). I tried some system cleaner / unblocker stuff which, although it didn't cure the pipes (had to replace them in the end), made a HUGE difference to the hot water output. Before we did it, you had to run a bath quite slowly or it would start running cold after the first 10 gallons or so. Now it can keep up with the demand even with the taps (almost) fully on. I might even make a point of using a system cleaner as a matter of course every (I dunno), 5 years?

The other thing I've wondered (bit of a thread drift, sorry!) is whether I should fit a room thermostat - possibly even one of those "smart" ones like "Hive" or similar. At present all the radiators have thermostatic valves on them but I'm wondering if we'll save a few bob uisng a room thermostat. I notice the controller has the facility for a room thermostat to be connected.
 
All combis give DHW priority. From cold, it will always heat up the heatstore before heating. You can fool it a little by turning the HW thermostat right down.
The addition of a room stat will always improve efficiency over TRV's.
 

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