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Efficiency of gas radiators?

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So, I know that I won't necessarily get an exact answer here, however is there anyway of measuring efficiency of gas radiators?

My boiler is 93% efficient, however I'd hazard a fuss that most radiators are 15 years old at the the very least, with ones in the attic being at least 11 years old

The house is very well insulated, with the only real possible improvements being internal wall insulation, and I'm currently able to heat the house with the lowest flow temp possibly to me on the boiler (40C albeit we're currently only in September, so I don't know how that'll fare come December to February)

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  • QrizB
    QrizB Posts: 13,822 Forumite
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    Radiators are all 100% efficient. All the heat that is lost from the radiator enters your home.
    What can sometimes happen is that they lose heating capacity, either internally (rust, sludge etc) or externally (people paint them or cover letter hem with decorative covers). This reduces their ability to lose heat but they remain 100% efficient.
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  • ABrass
    ABrass Posts: 1,005 Forumite
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    You mean effectiveness. Efficiency for a radiator isn't really meaningful.

    The main measure of if your radiators are working effectively is: are your rooms too cold or not? If you have over large radiators in some rooms then you'll get a lot of overshooting in the rooms. 

    A more scientific approach is to see if they are properly sized for the room by measuring the flow temperature drop. If they are well sized then you should have a consistent drop in temperature between the incoming supply to the radiator and the pipe leaving it. I believe in normal systems that expected to be 20 degrees difference, but that obviously won't be right for a system that only goes up to 40 degrees flow temperature.

    Balancing your system well, so all rooms heat up evenly might help reduce the amount of time you need to heat the house by avoiding cold spots, but with TRVs or worse smart TRVs it is less important and harder to do well.
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  • waqasahmed
    waqasahmed Posts: 1,940 Forumite
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    QrizB said:
    Radiators are all 100% efficient. All the heat that is lost from the radiator enters your home.
    What can sometimes happen is that they lose heating capacity, either internally (rust, sludge etc) or externally (people paint them or cover letter hem with decorative covers). This reduces their ability to lose heat but they remain 100% efficient.
    Sure. Like the other person, I didn't mean efficiency in terms of the scientific term given that 100% of the useful energy is converted to heat, and that's what you want however it is absolutely about potential effectiveness, and potential heat loss through pipes along the way / any sludge 
  • ABrass
    ABrass Posts: 1,005 Forumite
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    edited 26 September 2022 at 6:47PM
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    Sludge in the radiator would reduce the amount of heat the radiator can put out, mostly by slowing the flow rate I think. You'd find that the radiators aren't getting warm enough if it were an issue and probably just open up the lock shield valves a bit more.

    The pipes are more interesting. If they're on the inside of your houses insulation then they just act like very sparse underfloor heating. Any losses just warm a different part of your house. If they're outside the insulation layer then they will lose heat and should be lagged.
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