22mm copper pipe to supply radiators

[j0nb0y]

I have just been to look at a house that is on the market. The house looks like proper "bodger" has lived there, although the work required looks mainly cosmetic. It looks like it has had central heating installed fairly recently, I noticed that some of the radiators are supplied in 15mm copper tube, but some are supplied in 22mm. I have never known this before, is this normal???
It is a combi-boiler by the looks of it, as I noticed the tank had been removed from the airing cupboard.
Any answers would be much appreciated.

[The Builder]

Plumbers will argue all day about pipe sizing, jonners. It's good practice to have a main circuit(s) of 22mm to bring plenty of water to that point. Tappings are then made with 15mm to go to each rad. Actually, 15mm would supply more than one rad.
22mm to a rad must look unsightly as well as being unnecessary. Someone going rather OTT I guess. Should still work ok though if the circuits have been worked out properly.

[AlBags]

OTT .. But it will work ok.
Thing is, if you look at the orifice inside a TRV, you will realise you only really need the equivalent of 8mm! However, 15mm or larger keeps the flow reliable through all the corners .. and drag of the pipework on the head of pressure from the circulator pump.
I only fit 22mm on primary circuits these days, generally because of low volume rads, TRV's and less water content in systems overall.