Replacing rads on a single pipe system

[Richard1000]

Hi,

I need some basic advice regarding a single pipe central heating system. I have done some research on this type of system and have learnt some of the basics. Although I understand it is not a great system, we have just bought a house with the system. The system heats up the house well. However, we are thinking about upgrading/dating the radiators downstairs. This is because some have been painted, some are old panel radiators and some do not have the BTU capacity for the rooms (e.g. the lounge was extended and the new radiator was fitted for a room of the original size). However, in the main the radiators are the original. There are six radiators.

The first question I have is how do I know which way the water circulates the system? When the system is on all the radiators seem to heat up just as hot as each other. I tried following the pipes but it gets a bit confusing when they go under the floor.

To fit a TRV I understand I need a Full Flow Valve. Do I need to fit this in the inlet side of the radiator or does it not matter? Currently the TRV’s are fitted one side of some radiators and the other side others radiators.

Should I oversize the radiators to towards the end of the pipe run to compensate for the heat loss?

As with TRV’s are there any modern radiators more suited to a single pipe system than others? Currently we thought of replacing with Stelrad Streamline. However, I saw that some radiators have larger internal capacity than others thus making them better for a single pipe system. Space is not an issue and we could go for something like a Quinn Round Top which seems to be bigger if it would be better.

With a one pipe system is it better to single or double radiators or does it not matter?

When fitting the radiators it is better to take the feed to the top of the radiator rather than the bottom? Current all the feeds are to the bottom. I prefer this because it keeps all the pipe work at a low level, however is it less efficient?

The system uses a 22mm pipe for the main with 15mm into the radiators.

Is there anything else I need to know?

The reason why I am doing myself is because I am confident that I can but mainly becuase out of three trades men I called, only one turned up and his quoate was - £20,000 including a power flush and a bolier service. Such a quote has completely put me off about getting anyone in to do it.

Many thanks fro your help

Richard

 

[Agile]

If you want to do that much you might as well run a new return pipe but keep the present pipe as the flow.

Your system can work well but is not suited to a condensing boiler as that has lower flow/return temperatures.

Any replacements should be upsized to ensure they will work with a replacement condensing boiler. Assume flow 75 and return 55.

If you really must keep a one pipe then you would need to size the rads towards the return to provide enough heat at only 55°. They could be quite a bit larger but not impossibly!

You are very lucky having a 22 mm system as thats more versatile.

Another little trick is to split it into two loops by taking two new pipes into the middle but thats only usually worthwile on a 15 mm system.

Tony

 

[Richard1000]

Thanks.
Putting in a return is not an option - too much work, too expensive and I could not do it myself.

We have condensing Baxi 100 boiler on the system and the whole sytems works as good as any in my friends houses.

I just want to update the radiators like for like except where the odd one is undersized. I just had these basic questions before doing so.

Thanks.

 

[Agile]

If the boiler return is much above 55° then the boiler is not going to be doing much condensing!

You should keep the boiler stat temperature as low as possible comesurate with getting adequate heat output.

Here in London its +0.2 outside but 21.4° inside and its snowing hard and about 20 mm on the road.

Tony