Radiator pipe identification problem

[nemgreen]

I need to fit a new radiator in our bathroom.

I plan to tap into the pipes (plastic) running under the floor that feed a single bedroom radiator.

The problem is that I'm don't know which is the hot/outward pipe and which is the cooler/return.

How important is it that I identify the pipes correctly?

What would happen if I got them the wrong way round?

I don't expect to be using the termostatic control too much as this new radiator will be used for towel drying etc ..

All advice welcome

Thanks

[Mike Tomlinson]

In article , nemgreen writes

Turn the heating on from cold. The flow (outward) pipe will get hot first.

[fred]

In article , Mike Tomlinson writes

Good idea, though it is now less important to get them the right way round as most thermostatic radiator valves can take bidirectional flow. If a TRV is unidirectional it will have an arrow on its body indicating the required direction of flow and if bidirectional it will have a double ended arrow. Operating an older unidirectional one in the reverse direction usually causes rattling, vibration, or just failure to pass any water.

I should qualify that with: as long as you are using the bottom fittings at opposite ends for entry & exit (BBOE - Bottom Bottom Opposite End) it makes no difference, but if you are using a top fitting, either TBOE or TBSE then the top should be the flow (hotter).

Actually just noticed you are talking of a towel radiator so that should be bottom entry, but I'll leave the more complete answer instead of just deleting it :)