Central heating circuit design

[dashwo]

Hi,

I recently moved into a new house and I want to update the central heating pipes… the boiler is only a couple of years old (Gloworm Ultracom 30cxi) so I don’t intend replacing that but there’s a single pipe system running round the whole house over the floorboards so I’m planning on replacing that with a 2-pipe flow & return arrangement hidden under the floors.

After doing a bit of research, I’ve come up with the following plan…. using plastic speedfit pipe for the lot (apart from the first couple of metres from the boiler), starting with 22mm from the boiler, splitting to 2x22mm supplies for the upstairs and downstairs separately, teeing off in 15mm for each rad and then the end of each run reducing to 15mm to supply the last 2 rads – see diagram.

Untitled

• dashwo
• 18 Oct 2012
• 1

As this is the first time I’ve done anything on this scale, I have a couple of queries:

1) The boiler’s flow outlet is 22mm but has then been increased to 28mm after about 20cm – would it be better to continue with 28mm to the split point or as the initial outlet from the boiler is 22mm, is increasing it to 28mm relatively pointless?

2) Is it OK to split the flow & return pipes (22mm) into two 22mm runs to supply the upstairs and downstairs separately or would it be better having a single run for the whole house?

3) Does my planned arrangement look ok in general??

Any advice would be greatly appreciated.

Many thanks
Dave

 

[D_Hailsham]

Your diagram looks OK, but there are some preliminary steps before sizing the pipes:

1. Boiler sizing
I know you are not replacing the boiler, however it's worth checking that it is providing the correct central heating output. You use the Whole House Boiler Size Calculator to do this. If the requirement is much lower than the Ultracom's 23kW it's worthwhile turning the CH output down using parameter d.0. This does not affect the Hot Water output which is 30kW. See page 51/52 of the Installation Manual.

2. Radiator sizing
You need to know the outputs of your radiators. Hopefully they are flat steel, with or without fins, in which case you can use Stelrad Elite Catalogue, page 31.

3. Temperature differential
This is the difference between temperature of water leaving boiler and water returning to the boiler. The Ultracom is designed for a 20C difference at max output. If the total rad output is about the same as the required boiler size you will find it difficult achieve the 20C; but if the rads add up to 20%, or more, greater than the required boiler, you should have no problem achieving the 20C differential.

The pipe sizes will depend on the temperature differential.

See Small Bore heating Systems and Copper Tubes in Domestic Heating Systems

Although you are using plastic pipes the same rules apply when determining pipe sizes. You can find the info on speedfit pipe in their Catalogue, page 47. If you are using a 20C differential the capacity is increased in proportion to the temperature, i.e multiply the data given by 20/11.

 

[dcawkwell]

Convert system to a sealed system.
22 mm pipe is fine. THat is what the boiler is supplying so bigger is pointless
you won't get any more flow than a 22mm can supply.

 

[CBF]

Convert system to a sealed system

it's a combi so it already is a sealed system

 

[dcawkwell]

Convert system to a sealed system

it's a combi so it already is a sealed system

Didn't realise the loft was a radiator and I don't remember boiler model numbers. Life is too short.