How to install Radiators in Separate Annex building?

[paulrog]

Hi,

I'm wondering if anyone can help me, now i'm not a plumber but can install radiators/bathroom suites etc.

My question is this -

We have recently moved into our new house which is an established 3 bed semi, around 100 years old with a large garage built around 2 meters from it.
The garage was converted to an Annex building with a shower room, Kitchen, bedroom etc before we moved in. The Annex uses 2 electric storage heaters for heating, there is no gas in the Annex, just the main house.
We have had a new Worcester Hi-flo combi boiler installed in the main house, now i want to remove the 2 storage heaters and install 2 central heating radiators run off the main worcester boiler in the main house as this is the most energy efficiant way to heat the Annex building (I think?)
What is the best way to install the 2 pipes from the main building to the Annex building?, I would like to go underground as then they won't be seen?
I'm concerned with the winter freezing problems? Not sure to use either copper or plasic pipe?
Any other problems I should know?

Thanks for your help.

 

[stevetheplumber]

you can buy pipe in pipe plasic pre lagged but its horrendously expensive usual method is across at high level lagging and boxing which is then felted to water proof

 

[Best]

Can be a bit of a nightmare going underground with risk of damp & damage to damp courses etc. You could duct the pipes underground using 2 of 110mm waste pipes. One for each heavily lagged pipe. Ordinary underground sewer pipe is fine.
If you use copper pipes, the 110mm pipes & copper pipes may need installed in 2 pieces & the duct pipes finally joined in middle using slip connectors.
Plastic might be easier to an extent, but can be too rigid to work with if bending. I use copper. Just be sure to seal each 4" pipe through the walls below the ground with sand & cement if you do opt for underground.

 

[SimonG]

Wants to be on a seperate zone with a frost stat in the annex. My choice would be high level, but then I dont like digging

 

[MarkAqua]

the only way is pre-insulated pipe.

 

[Roger Welton]

I'd be putting in underground pipework on a separate heating zone. Are you putting in a small water cylinder to supply the kitchen / bathroom in the annexe or planning on running it off the combi also?

https://www.uponor.co.uk/solutions/local-heat-distribution.aspx

 

[Worcester]

We use pre-insulated all the time for this situation, however it is very inflexible and terminating it properly is very expensive and time consuming.

For a short 2m run, the simplest, easiest way (and I'll probably get shot down here ) would be to install a pair of buried 100mm flexible ducts - electricians use it all the time, and then pre-insulate your own plastic pipework, bear in mind that 28mm plastic has about the same ID as 22 mm copper, so run 28mm plastic with 25mm thick insulation (strangely our local B&Q stock this, none of the plumbers merchants do though! ) overall diameter now about 73mm, put the insulation on it first and the feed it through in a single length (3m long...) through the duct and seal the ends of the duct with expanding foam.

With no air movement in the duct it will also act as an insulator.

I'm guessing the hot water in the annex is also electric, and cold supply already there, so running a 28mm plastic pipe, it could easily be configured to heat a small (100 litre) DHW cylinder as well as the rads. Don't try to extend the combi HW side ...

Depends whether the existing system has a zone valve or not, being a combi, possibly not, so needs a zone valve in the house, and then run it as either Y or S plan in the annex with call for heat back to the boiler. (Run the heat resistant cable inside one of the ducts back to the house)