The logic of central heating & the timing of CH and DHW

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Chaps

Those of you that know will no doubt be able to answer this but it has me intrigued.

When using a boiler to heat the hot water in the morning, and the heating is on, is there a logical way that you should programme the hot water and heating to make best use of the energy released by the boiler?

Given the hot water comes on at x time in the morning for 1.5 hours to heat the tank (we have a 300 litre Megaflo) and the heating is on for about 2.5 hours. Should we have the hot water come on at the same time as the heating for the first 1,5 hours, or wait an hour for the heating to get going before setting the hot water to be heated?

I'm just intrigued as to what the most efficient method of using a single boiler to do two jobs is, given the example above?

Likewise, is there a calculation you can do that will work out how long a hot water tank will take to heat up? An hour and a half seems to do the job, but if I know that xx kw boiler will heat a xx litre tank in xx time, then I know how long to have the boiler on for to heat the water in the tank.

Just interested - call me a numb nut if you like, but I'm not sure if anyone has asked the question before or how best to search for such a question?

We have a 300 l Megaflo and LPG tank, (which is not cheap) and a Ferroli boiler - and a large house which although only 5 years old, takes a while to heat up at the moment, so with average gas bill of about £1500, if I can save it bit it helps...

Thanks

Andy

 

[D_Hailsham]

When using a boiler to heat the hot water in the morning, and the heating is on, is there a logical way that you should programme the hot water and heating to make best use of the energy released by the boiler?

Given the hot water comes on at x time in the morning for 1.5 hours to heat the tank (we have a 300 litre Megaflo) and the heating is on for about 2.5 hours. Should we have the hot water come on at the same time as the heating for the first 1,5 hours, or wait an hour for the heating to get going before setting the hot water to be heated?

Probably better to heat up HW and CH separately, but it would be difficult to prove without experiments. As the Megaflow has very good insulation you could always heat it up in the evening, after all the baths and showers, knowing that it will be still warm enough for the morning. You could then top it up in the middle of the day, when the house is warm and the CH is not running full tilt.

Likewise, is there a calculation you can do that will work out how long a hot water tank will take to heat up? An hour and a half seems to do the job, but if I know that xx kw boiler will heat a xx litre tank in xx time, then I know how long to have the boiler on for to heat the water in the tank.

The Megaflow Sales Leaflet has a graph showing how long it take to heat up, depending on boiler size

We have a 300 l Megaflo and LPG tank, (which is not cheap) and a Ferroli boiler - and a large house which although only 5 years old, takes a while to heat up at the moment, so with average gas bill of about £1500, if I can save it bit it helps...

Install a Honeywell CM900 series optimizing programmable thermometer.