Boiler efficiency question

[huw169]

Hi all
I need to replace my lead pipes into my property with plastic. When i do this, i could replace like for like, but with the amount of other work i am doing i can make some changes.

The current pipe runs under the floor in the void where it is cold, so in the winter when the boiler is used most, the water is very cold and the boiler has to work harder to heat it.

Would it be worth running the boiler supply pipe into the main living area first so it will warm up before it gets to the boiler? Would it save much, and is it worth it?
I have a route that would keep it concealed. Would alsmost be a 'pre-heater' for the water.
Thanks
Huw

 

[kevindgas]

don't waste your time by the time the boiler is up to temperature for hot water all the water from the street main will have gone down the plughole!

and you won't save as much as you will spend on the pipe!

 

[huw169]

Thanks Kev - thought as much.
Huw

 

[TicklyT]

If the heat is coming from your living room, then it's heat that's been generated by your boiler anyway, so there's no gain.

 

[huw169]

That's not strictly correct Tickly.
The house is designed to be heated from the inside & keep that heat in - insulation. With a sufficiently long pipe in the house (heat exchanger principal) it would mean that the water heater inlet temp would be higher meaning that the boiler would not have to work so hard as the temperature differential would not be so great.

To take kevins point, the cost of trying to make it work is not cost effective, but that is not to say the principal is not sound. After all, it is that basis for many devices out there.

 

[stem]

In principle
Tickly's right. If the cold water pipe passes through a warm room, and some of the heat (albeit a tiny amount) is taken from the room by conduction through the pipe into the water. That heat is lost from the warmer room (heated by the boiler) to the colder water. It's the same principle where room heat is conducted through glass, that heat too is lost from the room to the colder outside.

In practice
The amount of heat being considered is so tiny as to be negligible

Plastic pipe doesn't conduct heat as well as metallic pipes

Once the water in the indoor section of the pipe has been used, the incomming cold water won't be in the pipe long enough to pick up any heat

Cold pipe + warm room = condensation (you could of course insulate it but that defeats the whole topic of this thread then anyway)

In the summer, if water hasn't been used for some time, the water in the indoor section of pipe would have to be run off to get a nice cold drink.

 

[bengasman]

...The house is designed to be heated from the inside & keep that heat in - insulation. With a sufficiently long pipe in the house (heat exchanger principal) it would mean that the water heater inlet temp would be higher meaning that the boiler would not have to work so hard as the temperature differential would not be so great...

And where do you think the heat that you plan to use to pre-warm the water comes from?

 

[huw169]

I'm picking up a 'slight undertone' to the thread that this is probably not worth the effort.....

Cheers

 

[doitall]

Get a solar panel and a buffer tank, and you can pre-heat the water.