Drop radiators or not?

[danrhope]

Hello there,
We've just moved into a Victorian terrace and the central heating hasn't been touched since the 80s, so we want to upgrade the rads (amongst many many other things).

It's three floors, ground (with sub-floor), first and converted loft, and the boiler is on the first floor. The heating loop runs under the floorboards on the first, and drops down to each radiator, as on the diagram.

We are wondering whether or not to convert this to a single drop and then run across in the sub floor (in copper to avoid mice gnawing on the pipes), as on the second diagram. The kitchen is a concrete floor and will be extended in time with under-floor heating, so we'd keep that as it's own drop for the time-being. This way we were thinking there would only be one wall-chase to do and fewer opportunities for air-locks/complications when draining and refilling the system.

I would really appreciate your input please.

Best wishes
Dan

 

[Madrab]

All depends on the size of the rads that will be fed by the single drop to the ground floor

Using15mm pipe for the drop may be able to feed 2 radiators, if they aren't any larger than say 600x1000mm, without any impact to warm up times and overall heat but any larger then they may struggle to warm up properly and any more than 2 could cause problems with them heating up properly.

 

[danrhope]

Thanks Rob
And if I use 22mm for the drop, would that make a difference?
Cheers
Dan

 

[Madrab]

if I use 22mm for the drop, would that make a difference?

Yes - a 22mm pipe can carry/flow a lot more heat than a 15mm can, hence why most medium sized CH systems on average sized rads have a 22mm backbone with 15mm branches.

 

[danrhope]

Brilliant, ta.
So would you recommend 22mm all the way round the loop on the ground floor with 15mm going up to each radiator in turn? Or is it okay to just have 22mm for the up and down, and all 15mm on the ground floor?

 

[Madrab]

For a well balanced system in an older house where the rads are average K2(Type 22) rads that will heat up quickly, then CH design would recommend that the backbone i.e. all the main flow and return pipework, is run in 22mm and then all the branches from that to each rad in 15mm and kept as similar in length as possible

Modern highly insulated houses where smaller K1/P+(Type11/21) rads are installed then that system can be run in 22mm out to manifolds and then 10mm pipework used for the branches.

In an ideal setup, the main CH backbone would be run to a centralised location within the property and then branches out to the rads are kept as equal in length as possible. This allows for a system that all heats up at the same time and will be relatively self balancing.

 

[danrhope]

Thanks for the comprehensive advice Rob.
So actually, in terms of balancing, what i have now is not too bad? There is a 22mm main backbone, running around under the floor on the first floor, but the only negative thing is that each ground floor radiator is dropped from the first floor, which makes it a pain a) to chase all those pipes in, and b)to drain and refill the system.
We're currently getting off much of the old plaster and putting in new rads everywhere. I'd really love to avoid doing all that chasing in if it can be avoided, that's why I was hoping to create a loop on under the ground floor floarboards.

 

[Madrab]

Yes - if you can run a main flow and return to the ground floor and then branch out the those rads then it would be more standardised, that and run a flow and return drain out through the ground floor wall and that can then be used to drain the whole system if ever required - apart from the kitchen of course.