Measure boiler efficiency

Discussion in 'Plumbers' Talk' started by tellme_why, Aug 27, 2021.

  1. tellme_why

    tellme_why Member

    Hi,
    I have an old Potterton Profile 50e and the original manual shows 75% efficiency.
    On the other hand my gas bill is very high - 25,000 kwh/year for a rather small 3 bed house.
    Wondering whether the boiler efficiency degraded overtime or the installation was not sound.

    I'd like to measure the boiler efficiency or call in a service man to do it but I cannot find anything standard / pricing around. Last time I had the service done, the man didn't measure the exhaust flue CO/O2/ efficiency so no idea if anyone does this sort of thing?

    Many Thanks
     
  2. Starslikedust

    Starslikedust Active Member

  3. tellme_why

    tellme_why Member

    Thanks Star, but I am looking to hear how to measure the efficiency rather than read the boiler data sheet...
     
  4. Jimbo

    Jimbo Screwfix Select

    What does the EPC show as the annual energy demand (assuming you have one)
     
  5. tellme_why

    tellme_why Member

    Thanks EPC is D(60) "with potential to achieve D(67)"...
     
  6. tellme_why

    tellme_why Member

  7. Jimbo

    Jimbo Screwfix Select

    What date is the EPC? Further down it should give the actual space heating and water demand. The banding doesn’t correlate to a consumption btw, in that doc they are just averages.
     
  8. tellme_why

    tellme_why Member

    I am going to check, but does the service heating engineer test the boiler efficiency with flue gas device and how much does it cost?
     
  9. Baxi Boy

    Baxi Boy Active Member

    25,000 kWh is a lot for any house,about £1,000 a year!considering most is in the winter,and very little during summer.Any other appliances? Gas cooker? Fire? A lot depends on the heating useage,is someone at home all day in winter and heating on almost constantly? I have a two bedroom house,insulated,double glazed,with a combi condensing boiler and use 5,000 kWh per year.
    There are other considerations in gas use,are your radiators big enough for the rooms,or could they be partly sludged up? The boiler could be running overtime due to other things not being right.
     
  10. Mike83

    Mike83 Screwfix Select

    I use 11000 kWh per year.
    Modern condensing boiler. 4 bed detached.
    Newish build.
    Manufacturer states the boiler is 75% efficient.
    Combustion analysis only tells us how efficient the combustion is not the boiler. This figure will be higher than 75% if there’s no issues.
    Efficiency is lost at the boiler from the flue and the actual boiler itself as it gets hot so loses heat.
    The combustion efficiency can remain as it should providing the boiler is correctly serviced and cleaned.
    Overall efficiency is lost in many ways though.
    Poor boiler servicing.
    Poorly maintained system.
    Pipes not lagged.
    Poor home insulation.
    You could have the most efficient boiler on the market but it won’t do much good if the house is losing all the heat.
     
    ramseyman and Baxi Boy like this.
  11. tellme_why

    tellme_why Member

    Thanks, yes that’s alot hence I need to measure efficiency to decide whether a new boiler pays back in short time or whether it’s just badly isolated house. Anyone knows whether heating engineer can do flue gas analysis and how much does it cost?
     
  12. tellme_why

    tellme_why Member

    If the efficiency test turns out good then I know I don’t need to change the boiler.. heating pipes are flushed, no sludge, new radiators, underfloor pipes isolated. The only culprit could be the new decorative radiator take a lot of water, as they are not panel type..
     
  13. Mike83

    Mike83 Screwfix Select

    This could be a poor analogy but I’ll try.
    Imagine 2 identical car engines in 2 similar cars.
    One car is lighter and has more efficient tyres/wheels. The other is far heavier.
    Whilst both cars will have the same combustion efficiency they’ll have different m.p.g.
    So someone could check your boilers combustion efficiency and it could be fine but in reality it tells us nothing about how efficient the system is actually operating.
    Erp pumps and smart thermostats even contribute to overall system efficiency as does zoning and trv’s.
    Water quality reduces efficiency.
    A magnetic filter will even increase efficiency but not sure by how much.
    A condensing boiler will increase the boiler efficiency from 75% to over 90.
    Is your system wired correctly. Incorrectly wired or faulty zone valves could keep the boiler running and increase gas usage.
    Also your boiler is about 14kw maximum. This depends on the burner pressure setting though.
    Under high load conditions the boiler could be working flat out for a while.
     
  14. tellme_why

    tellme_why Member

    .. Thanks but my point is that if my boiler efficiency is 75% per OEM, changing to a new 90% the payback is 5+ years. If the boiler efficiency is no longer per oem , considering all other conditions equal, and say it’s 50%, the payback is 3 years in which case I replace it. I suspect the heat exchanger be affected by scale but the only way to know is measuring efficiency.. from what I read it seems nobody does flue gas test for small boilers.. industrial boilers is common and mandated ..
     
  15. Mike83

    Mike83 Screwfix Select

    A flue gas test won’t tell you how efficient the boiler is. It will only tell you the combustion efficiency.
    I’m not sure how you would actually test the boilers operating efficiency.
    Your boilers efficiency won’t be 75% now. It may be 65% but impossible to tell as the heat exchanger internals and pipework won’t be as new.
     
  16. adgjl

    adgjl Member

    What controls do you have? Room Thermostats, TRVs, Timeclock etc? I moved into a house many years ago and cut my gas bill in half simply by adding a room thermostat.
     
  17. tellme_why

    tellme_why Member

    I have TRVs per each radiator and one Hive. In winter it’s on 2h in the morning and 3h in the afternoon. Always off during night. Temperature set 22 max..
     
  18. Baxi Boy

    Baxi Boy Active Member

    Are you keeping your water tank storage set to constant? Water heating contributes to consumption considerably,is the tank fully insulated? Do you cook with gas?
    25,000kwh is simply a lot for one house when heating is only on for 5 hours a day in winter.Even if you had a 90% efficiency condenser boiler,all thing being equal it might drop to 21,000kwh,and with a combi further but still above average consumption by the sound of it.I would start to suspect a faulty gas meter.
     
    Last edited: Aug 28, 2021
  19. tellme_why

    tellme_why Member

    Hob burner would consume about 1,800kwh/year, so heating and hot water is 25k - 1.8k ..Gas meter is new, consumption pattern similar to previous gas meter. Hot water tank is 2 yrs old is on hive schedule from 1pm to 8pm, 60C set. Boiler start cycling only when power shower starts. 2 electric valves are brand new. I wonder whether the radiators could contribute to the issue; I have this type that takes a lot of water https://www.bestheating.com/milano-...er-radiator-635mm-x-1647mm-double-panel-79162 (two double large in the lounge), one small double at the entrance, one small single in the sun room and the reset is just panel radiators in the bedrooms..
     
  20. Baxi Boy

    Baxi Boy Active Member

    They are quite powerful radiators,@2.9 kw each,enough for a very large room of 8 metres x 6 metres,but that shouldn’t matter as they will heat a room very quickly and the thermostatic valves will shut them off.
    Although it’s an old boiler,made from 1988-2003,(it may have a pilot light running constantly if very old) I can’t understand the high consumption given the facts.The attic is insulated to 250mm minimum I assume,and double glazed windows? Cavity wall insulation helps but not suitable for every building.
    I would expect 15,000kwh maximum really,which could drop to 12,000 with a latest combi.
     

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