Seasonality of kWh used for hot water heating

theoretica

Sterlingtimes said:

May 635, June 473, July 359, August 381 and September 639.

How well do those numbers track the average temperature of the month?  If they track well, what happens when you extrapolate through winter?

Alnat1

How much water do you heat (tank size) to what temperature (thermostat on tank) how is it heated (temperature/flow control on gas boiler) and how long is it heated for (is a timer set)?

What do you need the hot water for (number of baths or showers a day, washing up etc) and do you actually use all the water you heat? Not saying this is you, but some keep 200l of water at 70C 24/7 for no real reason except habit.

Consider the above and it might be that you are heating too much hot water each day, to too high a temperature and making the gas boiler work harder than it needs to. 

By gradually reducing and adjusting we now heat our tank by gas (installing a solar diverter wasn't cost effective) for 40 minutes each morning. Tank thermostat is at 55C. Our boiler doesn't have temperatures on the flow dial but it's set about 1/3 of the way round. This gives enough hot water for 2 showers, hubby's shave and a bit left over for cleaning if needed. An average of 3.5kWh/day of gas was used Jun-date which includes a bit of hob cooking say 4 days a week.

I'm expecting we will need to adjust the boiler flow up a bit when the incoming water temperature drops over winter though. If one of us did want a bath, we'd hit the boost button for 15 minutes on the boiler controls and a kettle could be boiled if a random bucket of very hot water was needed.

Sea_Shell

QrizB said:

Sterlingtimes said:

During the months when my radiator heating tends to be zero, my hot water and cooking usage are as follows in kWh: May 635, June 473, July 359, August 381 and September 639.

I presume that in the colder months, the hot water will take more kWh to heat. Is there a rule of thumb that I can use to estimate my hot water usage during the months when I also use central heating? 

I don't know a rule of thumb, exactly, but if:

• You heat your water to 60C;
• In the summer months the incoming water is at 15C;
  
• In the winter months the incoming water is at 5C; and
• All other factors remain unchanged, then
  

Your winter energy use to heat water will be (60-5)/(60-15) ie. 55/45ths or 11/9ths of your summer energy use. That's about 22% more.

Thanks.   Very interesting.   Is that based on mains feed?

But what of hot water fed by a header tank in the loft😉😉😉.

Same calculation, just different perimeters?   Depending on how hot/cold your loft gets?

Sterlingtimes

Alnat1 said:

How much water do you heat (tank size) to what temperature (thermostat on tank) how is it heated (temperature/flow control on gas boiler) and how long is it heated for (is a timer set)?

Thank you, there are many helpful observations here. Unfortunately, it is difficult to control family behaviour in our household with mixed generations.

The worst offender for gas use is our 27-year-old Gretta Thunberg sympathiser, who insists upon a prolonged hot power shower.
 

daveaspy

wild666 said:

My monthly usage of gas is around £4.20 with £8.33 SC. My combi boiler doesn't seem to have a function for stopping the preheating of water it's a Valiant ecotech pro 28.
If you can turn off a function to preheat water do it and lower temperatures to 50 degrees for water and 55 degrees for heating.

It doesn't look like an Ecotech pro 28 has an internal water tank for preheating water (at least from the manual I just found online)

I have a Worcester combi that does have an internal tank, preheating turned off though (ECO mode) unless somebody begs for a bath