According to the Heat Geek cheat pipe sizing sheet (which seems to have disappeared form the heat geek site but is reproduced here 22mm copper is good for 6kW @DT5.  That means that 22mm plastic, and its a single pipe (you describe it as teeing off via a right angle connector which I dont exactly understand), then is a bit marginal, but the HC calcs are based on 0.9m/s and many would say you can go a bit faster.  Of course the run before it splits to the first rads is fairly short, its also less likely to be a problem, and if you have to run at DT6 the performance penalty is only 1.5% or thereabouts.

If it were my house I would very definitely 'suck it and see'.  Very likely it will work at DT5, if not a tweak will almost certainly get it to work.  It might be worth replacing that plastic elbow (if that is what it is) with a swept bend or copper elbow though whilst its drained down.

Posted by: @jamespa

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According to the Heat Geek cheat pipe sizing sheet (which seems to have disappeared form the heat geek site but is reproduced here 22mm copper is good for 6kW @DT5.  That means that 22mm plastic, and its a single pipe (you describe it as teeing off via a right angle connector which I dont exactly understand), then is a bit marginal, but the HC calcs are based on 0.9m/s and many would say you can go a bit faster.  Of course the run before it splits to the first rads is fairly short, its also less likely to be a problem, and if you have to run at DT6 the performance penalty is only 1.5% or thereabouts.

If it were my house I would very definitely 'suck it and see'.  Very likely it will work at DT5, if not a tweak will almost certainly get it to work.  It might be worth replacing that plastic elbow (if that is what it is) with a swept bend or copper elbow though whilst its drained down.

 

Yes, an elbow is what I should have said.

The 22mm copper pipe from the boiler curves slightly into the ceiling and then the push fit elbow connects to the horizontal run of plastic pipe under the 1st floor floorboards.

The copper pipe is about 1.5m into the ceiling which is directly below the first radiator, so I'd expect the first tee from the plastic pipe to be no more than 2m.

The HP will be fitted  on the same wall as the boiler and the run of 28mm primaries will be around 2m, so about 4m or so to the ceiling where the 22mm copper and plastic pipes are joined.

If I need to run at dt6, would that only be required in the colder months?

Posted by: @bash

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If I need to run at dt6, would that only be required in the colder months?

In principle yes.  Some heat pumps (I think including Daikin) appear to modulate the water pump to achieve a quasi fixed DT.  So if you set it at 6 for the cold months it may stay at 6 even in the warmer months.  There are probably some installer settings to control the water pump behaviour which you may well be able to tweak if it comes to that.