Converting single pipe CH to two pipe

K

Kurt000

New Member
I have a single pipe central heating system which was extended 20 years ago when we had an extension. The heating upstairs has never been great particularly in the extended part with only a few of the original radiators getting very hot. We replaced the downstairs radiators with UFH which I thought would improve the heating upstairs but it seems to have had little effect. Because of this I am looking at changing the upstairs to a 2-pipe system and have a number of questions.

1. The existing pipe work is copper but I am looking at using plastic for ease. I presume there is no problem with mixing the two?

2. To reduce number of connections I am hoping to use 22mmspeedfit lay flat pipe rolls. How flexible are these for feeding under the floor and do they straighten easily or do I need pipe clips?

3. Do I need to use swept tees at the radiator tails?

4. I assume the feed to the radiator should be on the TRV side?

5. I am splitting the feed to the radiators to reduce the length as currently it goes right round the house on a bit of a circuitous route. I will end up with 3 circuits and 4 different routes for the returns so there will be a number of tees on the supply and returns. Is there any issue with having a number of T’s.

6. I have one radiator downstairs which will be very difficult to convert. Is there any issue with leaving this as is?

7. I assume inhibitors such as Sentinel are okay to use with plastic?

Any help/advice welcome. Thanks
 
1. No
2. If notching the joists, check the rules for depth, and use clips in the notches. If drilling and threading, probably won't need clips provided joist spacing meets clipping distance rules. Pipes should be insulated.
3. No.
4. Most modern TRVs are bi-directional. If you use bi-directional TRVs it doesn't matter which side is flow or return.
5. If you have a hot water cylinder, the tee into the return from the cylinder MUST be the last tee before the boiler's return.
6. If you leave it as a one pipe radiator in an otherwise two pipe circuit, it will limit the flow to other radiators, and alter the flow temperature to them. If it is fitted in parallel with another circuit, it effectively becomes a two pipe radiator.
7. Yes.
 
Thanks for your reply Andy. That gives me more confidence about what I was proposing. The TRV's are already on the existing radiators so is there a way of telling if they are bi directional?

As for my point 6, I realise that leaving one of the radiators as a one pipe arrangement will affect the efficiency of subsequent radiators but there is only one following this and the pipe run will be much shorter so I think the subsequent radiator will still get a lot hotter than it previously did.
 
Bi-directional TRVs usually have a small right angle embossed on them with an arrow head at each end pointing away from each other.
 
andy48 said:
Bi-directional TRVs usually have a small right angle embossed on them with an arrow head at each end pointing away from each other.
Click to expand...
Checked and all TRVs are bi directional so will avoid me having to swap them round. Thanks Andy.
 
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