Microbore downstairs, standard upstairs?

[igbt]

Hi, I've recently moved into a house that has 8mm microbore connections to radiators downstairs and 15mm (standard?) connections to radiators upstairs. I would have thought that central heating systems would either be one or the other rather than a mixture, is this fairly normal practice?

Also, I'm trying to figure out how the system would be connected, would the upstairs radiator network have to be connected in series with the microbore network?

Thanks in advance for your comments.

 

[swbjackson]

It's common practice in new build. Microbore running down behind the plasterboard. Probably all run off loops upstairs.

 

[igbt]

Thanks swbjackson for your reply. so just for my ignorance, could you clarify what you mean by being run off of loops up stairs?