My boiler was set to heat my radiators to 75 degrees. When I had my annual check done, the engineer said it should be set to 60 degrees because that is a more efficient temperature.
What I don’t understand is why is that more efficient in the long run. Yes, the water is heated to a lower temp saving fuel, but now I have to run the heating for longer to get the house warm. Does having the heating on for longer not just cancel about any benefit from lowering the flow temp?
In: 8
It’s because natural gas (like most fuels) is a ~~carbohydrate~~ hydrocarbon, carbon & hydrogen, CH4 in this case. Burn CH4 and you get CO2 & H2O, water vapour.
There is a lot of energy involved in turning liquid water into water vapour (or vice versa), the latent heat of vaporisation; it’s a lot*. If the boiler return temperature is kept below 46 degC, that water vapour condenses and the latent heat of vaporisation is released and warms up the flue gases. That heat can then be recovered by the boiler. You get more of the energy going into the water in the boiler’s heat exchanger.
* You probably can’t get a mental image of how much energy is involved in turning 1 litre of water into vapour or back again. It takes more energy to evaporate a kilogram of water than it does to melt a kilogram of iron. That’s a lot of energy.
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