Adding new rads to a existing heating

[AdamD]

Hi

I have add two new rads to an newly completed extension. To enable the chippy to complete the extension floor I put the 22mm flow and return in to feed the new rads leaving it ready to connect to the existing heating under the kitchen floor. The floor in the extension is now down and i have lifted the kitchen floor to connect the new 22mm to the existing heating only to find all the pipwork under the kitchen floor is 15mm. I dont want to take up all the floors to find 22mm to connect unless I have to. Can I connect the new 22mm to the existing 15mm to feed the new rads or will I get problems?

 

[DP]

Pipe would normanlly be sized to carry a specific load. Some people bang the pipe in hoping it will suffice.

If the kichen branch is sized to carry the water requirements for that branch, tee'ing off additional radiators might lead to inadequate water quantity requirements for all the rads on the kitchen branch. If this does happen to you, you could uprate the 15mm to 22mm.

 

[AdamD]

I see, my concern is I would be going from 15mm(existing pipe) upto 22mm (new pipe) then back to 15mm (tails for new rads) rather than reducing from 22mm to 15mm as I normally would.

There aren't actually any rads in the kitechen, the existing pipe work feeds rads in the lounge, bathroom and bedrooms(we live in a bungalow). are you saying i should replace the existing 15mm with 22mm or just join to it?