Central Heating/ Hot water Question

[Mavster]

If you put the hot water on for a 1 hour session 1st thing in the morning at home, does it cost any more to put the heating on for that same 1 hour session ?

My logic is that its the same gas used to heat hot water and radiators simultaneously, or is my calculation flawed ? Perhaps heating radiators requires boiler to be on for the entire hour, whereas the hot water heating only might not? (Our system has a hot water cylinder).

Just curious really, but might help us keep warmer

 

[CatmanV2]

If you put the hot water on for a 1 hour session 1st thing in the morning at home, does it cost any more to put the heating on for that same 1 hour session ?

My logic is that its the same gas used to heat hot water and radiators simultaneously, or is my calculation flawed ? Perhaps heating radiators requires boiler to be on for the entire hour, whereas the hot water heating only might not? (Our system has a hot water cylinder).

Just curious really, but might help us keep warmer

You're heating more stuff so either:
a) You'll use more gas (in which case it'll cost more, e.g. the boiler isn't burning at full throttle, or isn't burning for the whole hour)
b) The water temperature will be lower after the hour. (In which case it'll cost the same)

First law of thermodynamics.

<sits back and calmly waits for @Zep to explain in detail why I'm wrong>

C

 

[mjheathcote]

If you put the hot water on for a 1 hour session 1st thing in the morning at home, does it cost any more to put the heating on for that same 1 hour session ?

My logic is that its the same gas used to heat hot water and radiators simultaneously, or is my calculation flawed ? Perhaps heating radiators requires boiler to be on for the entire hour, whereas the hot water heating only might not? (Our system has a hot water cylinder).

Just curious really, but might help us keep warmer

Flawed, unfortunately.
Heat is taken out of the water to heat your hot water cylinder, and heat is taken out of the water to eat your radiators.
Your boiler consuming gas has to provide this energy for both.
You therefore don't get any free heat, it all has to be paid for!

 

[safrane]

You are heating more, so it will cost more - the returning water will be cooler causing the cylinder to cool slightly and therefore require more 'heat' to keep to the desired temp.

Rather like using your heater matrix to assist cooling down a car if you have a dodgy rad.

 

[mowlas]

Also I know my boiler model has separate burners for water and heating so absolutely no efficiency savings to be had by burning them together.

However it is worth turning the temperature of the burners themselves down to a level where they still heat water and radiators sufficiently as that will burn less fuel and cost less. A bit of trial and error time finding that 'sweet spot' temperature is worth investing in.

 

[safrane]

I think you will need to turn the temp down on the water and rads, but as you say there is a sweet spot to avoid each being at a level that fails to do its job.

 

[Wattie]

2 years ago, can you imagine this thread?

 

[lifes2short]

even the wife is now banging on about why the bathroom radiators come on with the hot water heating, been doing it for the last 14 years

 

[lifes2short]

and our fecking boiler has packed in twice in the last few days now, bloomin thing does virtually nothing all year apart from hot water and when you need it the most fecking thing gives up

 

[Geo]

and our fecking boiler has packed in twice in the last few days now, bloomin thing does virtually nothing all year apart from hot water and when you need it the most fecking thing gives up

A bit like cars, they only fail when you want to use then.

 

[DLax69]

...I assume (perhaps wrongly) that you are using indirect tank heating for potable water purposes...? With recirc pump on the hot water line(s), and zoned heating...? Eh, topic I'm too dangerous on.