Convert central heating to twin pipe

[Geoff Pearson]

I'm planning to convert the ground floor central heating system from the old one pipe system to the twin pipe system. This partly because it is 50 years old and may be a bit messy and partly because I wan to be more efficient. I may add some radiators while I am doing it. There are 6 radiators in 5 rooms covering 14 metres by 10 metres. Upstairs is micro bore off a manifold. In all we have 14 radiators..

Currently the pipe is 15 mm copper. What should I use for my new system: 15 mm copper again? 22mm for part of the route? If I use plastic, which will be easier as I am working under the house, what size then? And what pipe? And any advice?

I'm not starting this until the warmer weather (ha!) but I am hoping the Council will install under floor insulation so I need to think about doing it soon, if that comes off. Later next year, I may have the boiler replaced with a Worcester Bosch 24RI.

Geoff

[Roger Mills]

What is the total heat output of your downstairs radiators? The rule of thumb says that 15mm pipe will support about 6kW worth of radiators. More than that, and some of the pipework should be 22mm.

If you use plastic, make sure it's barrier pipe (maybe it all is nowadays?). Plastic is easier to feed through awkward places, but also needs more support - otherwise it will sag, and make airlocks more likely. Whichever you use, I'd come up through the floor to the rads in copper. You can join copper to plastic under the floorboards.

[Geoff Pearson]

Many thanks - useful help. I think the 6 rads will total more than 6kW and definitely if I add two more. The under floor area is divided up in the same layout as the rooms above which makes getting decent lengths of copper down there awkward but not insurmountable - and would be my preference. The working space is 1.5 metres high. The bore of plastic is much less than that of copper so if 15mm copper is only marginally OK ,then it would have to be 22mm plastic and that is heavy and cumbersome.

Geoff

[fred]

In article , Geoff Pearson writes

As you have plenty of room underfloor you may wish to run 15mm plastic to each downstairs room to permit possible zoning in future. I have a zone per room capability here (not fully exercised) and given your previous posts on energy saving it might be of benefit. For info, I have found separate pipe insulation more effective than burying unlagged pipes in suspended underfloor insulation.

[Geoff Pearson]

fred

The Energy Savings Trust is sending a surveyor early in the new year - I may qualify for Edinburgh's free under floor insulation and I plan to pick brains while the surveyor is here. The zoning is an interesting thought. Is there a diagram anywhere of this?

Geoff

[newshound]

Not rocket science, you just fit a two port electrically operated valve either in the flow or the return of each "zone". Design your zones according to the way you use the house.

[fred]

In article , Geoff Pearson writes

Possibly a bit simple for a diagram, I just took 15mm flow and return pipes from all rooms back to a central location.

You can then choose what you want to do with them, either common them up off a manifold or split them into groups for zones controlled by 2 port zone valves. The benefit of taking them all back is versatility, you can experiment to see what works for you and using plastic makes changes relatively easy. The boiler pipework and that of the manifolds is on copper for rigidity and to satisfy boiler overheat requirements.

All my pipework has individual isolators so I can leave the system running whist working on another part if needs be.

The more zones you have the more complex it becomes as no-one really caters for this except in truly bespoke (and expensive) systems. Controls can be relatively simple however if you use a thermal store but adding a zone valve and a thermostat per room gets a bit pricey.