Heating system advice

[bernardgreen]

Probably not quite as cost effective as a combi but the water will be hotter

The cost effectiveness ( or absolute efficiency ) of combi boilers supplying hot water varies with the way the hot water is drawn. One long draw or many short draws of the same total volume of hot water produced. Many short draws tend to be lower efficiency than one long draw, hence depending on how you use hot water a cylinder ( one long burn to heat it ) may be more cost effective that hot water direct from the combi.

 

[Dan Robinson]

Jesus Bernie!

The OP only u uses the cylinder water for a sink and basins. In which case, no matter how the water is drawn, a small combi is going to be more efficient.

 

[bernardgreen]

Science Dan.

Hot water does not come out of a combi until the primary heat exchanger has been heated, then the water circulating between primary and secondary heat exchangers has to be heated, then the secondary heat exchanger has to be heated ( by that circulating water ) before heat reaches the water that is already flowing through the boiler on its way to the tap.

Then when the tap is turned off the two heat exchangers, the water circulating between them and the pump that was also heated by the water it was circulating all start to cool down and that heat is lost.

Add to that any gas wasted in pre-ignition purges or processes each time a tap is turned on and the water that flows ( probably wasted ) before heat reaches the hot water outlet and the cost effectiveness of a combi used for short draw offs os likely to be significantly lower than the same boiler used for one long continuous run of hot water,

 

[bernardgreen]

Jesus Bernie!

Ah I see it now......... Jesus and his ability to work miracles was involved in the design of some boilers........

 

[Dan Robinson]

Thank you for confirming that you know sod all about modern heating and hot water systems.

Get back in your boxm

 

[bernardgreen]

Thank you for confirming that you know sod all about modern heating and hot water systems.

If that refers to me not mentioning boilers that have only one heat exchanger with two water circuits then I will agree that I did not mention them. Provided the mass of metal and central heating water in the single heat exchanger is minimal then these twin circuit heat exchanges have a smaller differential of efficency between single long draw and multiple short draws of hot water.

 

[Dan Robinson]

No Bernie it didn't.

 

[Doggit]

Hi Chippie, there might be a programmer problem, and there might be a 3 port valve issue as well, but going back to your original post, you'd be converting a vented system to a pressurised system, and if the pipes are old, you may get a few leaks, or the plumber was good, and everything will be fine. Can you get the flue to an outside wall from the cupboard in an acceptable location.

You do shift work, but don't mention any kids etc, and in converting the loft, will there be more people using the hot water, as an unvented cylinder may then be more sensible, or a larger combi might be easier if there are space issue. You need to get the pressure and flow checked, but in essence, the jobs feasible. Remember that without a good flow on the incoming mains, you can get fun and games if you're in the shower, and someone flushes the loo.

 

[aptsys]

Ah I see it now......... Jesus and his ability to work miracles was involved in the design of some boilers........

I don't see anything incorrect there. Can you explain please?

 

[Mottie]

Strange that the OP is concerned about efficiency yet uses an electric shower.

 

[bernardgreen]

Strange that the OP is concerned about efficiency yet uses an electric shower.

Efficiency and cost effective use of fuel are not the same thing.

Electric water heating is almost 100 % efficient as there are no flue gases taking heat energy away into the atmosphere. But as electricity costs more than gas per unit of heat energy a gas boiler can be less than 100% efficient but still return lower costs for heating water.

 

[Doggit]

Strange that the OP is concerned about efficiency yet uses an electric shower

But most people don't realise until someone smarter points it out.

 

[Mottie]

Efficiency and cost effective use of fuel are not the same thing.

Electric water heating is almost 100 % efficient as there are no flue gases taking heat energy away into the atmosphere. But as electricity costs more than gas per unit of heat energy a gas boiler can be less than 100% efficient but still return lower costs for heating water.

That was my point, you know what I meant, you’re just being picky. I’m sure I’ve seen it on here a couple of times that to heat a given amount of water, electricity costs about 4 times the price of gas.