Plumbing my central heating?

am going to be plumbing my central heating (not the boiler).
I am not sure if I should use 15mm or 10mm from the main runs to th radiators!
As I see it there are Pros and Cons to each, as I see them:
10mm (microbore) is easier to work with, requires less notching o joists, and I can burry it easily in conduit in the wall and there i less water in the system to heat up (reducing the cost of warm up). But its not much cheaper than 15mm, it comes on coils and can be messy I have my doubts if it can deliver to any radiator over 2500 BTU and wonder if the radiators will take longer to heat up in addition th heat loss will be greater than from a 15mm pipe.
15mm it neater (straight lengths) it can definitely supply upto 1000 BTU, it looses less heat and should get the radiators quick faster. But it is difficult to run through 20mm conduit and 25mm conduit i stone is hard damn work (I don't want it in chunky trunking cause tha looks worse than the pipes directly on the surface). Also I am heatin a lot of water during the warm up phase that I do not need to.
All of this is based on my limited knowledge, any advice would be muc appreciated. Which system is more efficient?
Do you get cool rads with 10mm (I know you do with 8mm)?
Thanks
and
-- andymason79
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andymason79 wrote:

My preference is for 22mm from heat source, branching off to 15mm to the radiators. Lots of capacity, and very few air locks. However, if you need to chase in a lot of it, how about doing the branches in microbore? This will give you all the capacity you need, while allowing you to bury it easily where necessary.
--
Grunff

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On Mon, 7 Nov 2005 18:29:57 +0000, andymason79

10mm or even 8mm pipe is not magically different to any other size - you just need to use it appropriately.
I have 8mm pipe throughout the house and designed the system to use it.
If you are getting cool radiators with 8mm, then it suggests that the radiators are too large, the pump setting isn't high enough, the valves aren't open properly or there is a blockage.
Heat transfer depends on flow rate and temperature drop designed across the boiler and radiators. The limiting factor is the linear speed of water through the pipes and that in turn determines the mass of water per unit time that can be transferred. There are application notes and tables at the Copper Development Association web site which cover this.
Over a few metres (as in typical in a house with several manifolds), you can get about 1500W through 8mm and 2500W through 10mm pipe - certainly more than 2500BTU. I don't use the old units because of the risk of arithmetic errors and because it's bad practice to mix units of measure.
I changed my boiler a couple of years ago and redesigned the temperature parameters. If you are fitting a new condensing boiler, you can run with flow and return temperatures of 70 and 50 degrees respectively as against the older 82 and 70 degree of conventional boilers. This does mean that the radiators need to be physically larger or have more fins to achieve the same heat output as before, but has the advantages that the radiators are not so hot to the touch and the boiler runs more efficiently. Moreover, you can get more heat through a given pipe size because you have nearly twice the temperature drop as before.
I was able to achieve the changeover by moving some radiators around and replacing three with larger ones. On a new system, it would be possible to pick suitable ones from the outset.
I had only one location which needed a 4kW radiator that is run in 15mm.
If you calculate the water content in the system, most of it is accounted for by the radiators. There is not a great deal of difference in the total represented by whether 10mm or 15mm tube is used for the radiator runs - might be 5 - 10 litres in a 100 litre system.
Regarding warm up time of the raditors, I have not noticed anything different between those connected with 8mm and 15mm - there shouldn't be when the system is balanced. The more important point is whether the air temperature is what you want it to be when you want it to be. That will also depend on the fabric of the house and its thermal mass.
I've dealt with this issue using weather compensating controls and a thermostat controller that learns the house characteristics. I have it organised for night set-back - typically down to about 15 degrees where it would normally be 20. The boiler comes on in good time and modulates. If there is a large temperature rise to be achieved in a short time it will increase output. Otherwise it warms more slowly and doesn't overshoot the desired room temperatures.
I think that dealing wiht the installation issues is more important. As long as you design correctly, there is no reason why 15mm should be needed except on the largest radiators. The important point is to locate manifolds so that pipe runs can be kept fairly short. You don't want 20m runs of 8mm. You don't *have* to have manifolds either. You can run 8 or 10mm from branches on the 22mm main runs.
--

.andy


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I ran 22mm. pipe for the main flow and return to the boiler. These two pipes were quite close to the walls which allowed me to run 10mm. tails (about 18 inches long) to each end of the radiators. The main pipes had 22mm. to 10mm. "Tees" fitted. When it came to running the fed and return pipes upstairs I used 15mm. as there are only three radiators upstairs.
Chris.
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andymason79 Wrote:

the gas industry is verging away from microbore type systems as the are known to fur-up and block more readily...however they dont bloc every day or every year or even in the next 15 years...after tha however there is a risk....ever thought of coated and coiled 15m copper pipe??? i believe its on the market now.....{plastic is not m favourite pipe} but that could be an option for you also....would no recommend speed fit type fittings...use ordinary comp fittings wit metal incerts on plastic pipes...
-- gastec
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Not him again. Look at what he says....

Which part? Which area?

Who told you that? A sealed system, with inhibitor and microbore will NOT fur up.

And nver if inhibitor is fitted every 4 years.

What risk?

My word he has redeemed himself with lots of sense .
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gastec wrote:

Who are "the gas industry"? Dodgy plumbers?
> would not

Because?
--
Grunff

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