Expanded Central Heating System Design

7 Jan 2010
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United Kingdom
I'm looking to expand my central heating system by adding a new bathroom UFH zone. I'm also changing the pipes feeding the loft radiators to 22mm, instead of 15mm.

Early discussions with my heating engineer talked about introducing a Low Loss Header and one or more additional pumps.

The existing layout can be seen here:
View media item 105123Here's my view of what the new design might look like:
View media item 105124
The loft radiators have had flow issues and the plastic piping feeding them was completely blocked by silt so they were never warming up. I have now cleared the pipes and want to introduce a 22mm feed from nearer the boiler as they were previously feed from the last radiator on the first floor. I will also re-route the loft pipes so they are no longer in a "star" shape, but are connected in parallel. Hopefully, along with an additional pump somewhere, this will ensure the loft radiator pipes don't silt up again due to their increased flow.

The new bathroom UFH manifold will be connected by 22mm pipes and will require either an actuator on the manifold (only one of the ports will be used) or a valve, controlled by a VR 91 thermostat in the bathroom.

One issue I have is the running of TWO new sets of 22mm flow and return pipes from (near) the boiler to the bathroom and loft. There is a landing floor spanning from one end of the house (where the boiler is), to the other end of the house (where the bathroom and loft pipes are) along which 4 x 15mm pipes currently run, notched into the joists.

Notching in another 4 x 22mm pipes seems like a none starter as does drilling 4 x 25mm holes into each joist.

I was wondering if the loft radiator circuit and the bathroom UFH manifold could somehow be supplied by a single pair of 22mm pipes (supply and return). I think the difficulty doing this would be the valve control as they are both separate zones!

Also, I'm wondering if it is better to have a single additional pump after the LLH, or possibly a pump for each zone? Given that both UFH manifolds already have built in pumps, this seems like overkill. So, potentially, a pump after the LLH would improve the CH flow and get the water to the two manifolds, where the manifold pumps would get it around the UFH circuits.

I would appreciate any thoughts you might have on the considered changes.
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Here's what I was thinking of in terms of having only one pair of 22mm pipes (flow and return) feeding the new bathroom UFH manifold AND the loft radiators:
View media item 105125
The valve shown on the supply to the loft radiators would have to open/close in sync with the existing valve on the CH supply near the boiler. I assume this is possible.

I also assume having a single 22mm supply to the new bathroom UFH and loft radiators wouldn't be an issue, especially if a new pump is installed after the LLH.

Would the new pump need to be setup such that it came on in sync with the boiler pump? Not sure what the requirements are for the LLH (I confess I don't fully understand how these work).

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