Efficiency of heating DHW by gas

Sterlingtimes

phsci wrote: »

The efficiency for hot water production only is a mere 49.7%, and then there will be transmission losses between your boiler and the hot water storage cylinder. I believe this makes a good case for continuing to use your immersion diverter and sacrificing your export payments (if and when they are measured) in fa ...

Thank you, phsci. Wonderful posting on your part. This is exactly what I was looking for. I had a feeling the summer efficiency could be far lower.

That makes the decision for me. I will continue with diversion and suffer the lower export payment.

Regards, Sterling.

Sterlingtimes

HappyMJ wrote: »

Be careful of that hot water figure of 49.7% it is measured in test conditions and takes into account losses in the pipes between the boiler and cylinder (they use 1.5m of pipework in the test), losses from the cylinder (they use a 120 litre insulated cylinder) and losses from the tap when you run it for a period of time waiting for useful hot water to come through.

My economic threshold between the decision to heat water by solar or gas is based upon 62%.

So if the summer boiler efficiency is 68% (as quoted in the stats) and I have some loss in several metres of pipework then I am probably already falling below the 62% threshold.

The losses in the cylinder and delivery to the water outlet (as you have stated) are neutral in my calculation.