2 pipe to 4 pipe system

[clion]

All,
I have an existing 2 pipe system which I installed in detached garage 16 yrs ago.28 mm pipe to manifolds and then to the rads,with new Danfoss control system(brilliant).
Question.
I have built an office which is on the unused pipe side of the boiler,and I propose to pipe from these outlets to a single rad.Anybody have any theories on whether I should run with 28mm then to micro bore ,or 28mm down to 12mm with or without a pump.If I run without a pump will the existing 2 pipe system be robbed of heat.The system is on same level i.e. a bungalow.
Ta.

 

[oilman]

Any heat into your new radiator will be "robbing" the existing system, but then that was the point of putting the radiator in - to provide heat.

If you don't have a pump on the new take-offs, then you will have a gravity system, it won't be helped by the other pump because the boiler is a pressure neutral point. You will need to run with 28mm pipe to get good gravity circulation, but this would not comply with building regs part L. Put a pump to feed your new radiator if you dont want to disturb the existing pipework. Unless you have plans to expand the system or it is a VERY large radiator you could use 15mm pipe everywhere on the circuit with a pump running on speed 1. You could use smaller pipe, but that has long term problems unless you regularly maintain the heating system. Most people don't.

 

[ChrisR]

Also be careful about where your vent and feed/expansion pipe are. If you put your new pump effectively between them, you could end up sucking air or "pumping over".

 

[clion]

Thanks for the replies guys.I am going to run with the "gravity"option for now but make provision for a pump.The existing setup has the boiler in a detached garage and piped to the bungalow with 28 mm.The heating is via micro bore and the manifolds are inside so almost impossible to link to them...going different direction.Her indoors would not like the solid floors renewed!.
Regards.

 

[oilman]

Just be aware that the gravity circulation will no longer meet the building regulations. Theoretically you should have building control approval. It may cause you problems when you come to sell the house and the buyers solicitor wants the questions answered, and they will be looking for a lever to reduce the price. A pump and valves will cost less than £40 and about £10 for a thermostat. The advantage is you can control the temperature in the room.

Designing for gravity is a bit difficult, and will be even more difficult for you as the boiler will switch off when the other system is satisfied. If your extension is too cold the boiler wont know.

You will save money on fittings by using 15mm pipes, which could go towards the pump etc.

 

[ChrisR]

Gravity HW is agin the regs but is gravity red circulation too? No reason why the office couldn't be a separate zone even if not pumped.

 

[clion]

Guys,
Just to let you know,boilers have ears and feelings.After all the discussions,the oil pump solenoid decided that it didn't want to play anymore.Really nice because I think the boiler spares place(the only local one that does Danfoss)is shut until Monday...Regarding the radiator,I have taken the easy option for now and will use an electric heater until the weather warms up,I will have to route the pipes behind some of my metal turning machines and Sods law says I will get the blame if something else breaks,so to placate her indoors and keep me out of the workshop in the evening, I have agreed to do some decorating......
Bye

 

[oilman]

I have some of those, whereabouts are you?

 

[clion]

Thanks for the offer,got one from another supplier.All is now well and any talk of playing with the boiler will take place well out of earshot of the old dear(you decide which old boiler I'm refering to!)
Bye

 

[ChrisR]

Fancy calling a boiler "the old dear". I do talk to them sometimes but never tried that one.