Radiant Heat Question

I recently bought a new home that has radiant heat flooring in the kitchen and the adjacent bathroom.
The bathroom was remodelled about 1 year ago and the kitchen was remodled about 4 years ago both with radiant heat .
Here is the problem.... when they remodeled the kitchen they used 1/2" tubing and when they remodeled the adjacent bathroom they used 5/16 " tubes and tied the new bathroom into the kitchen zone, now the bathroom is about 6 degrees cooler than the kitchen.
I called a couple of plumbers and they advised me that 5/16 size tubing was suffiient to heat that size bathroom (bathroom is about 5'x4') .

Some significant background information on the house and layout.
1.The kitchen is on the first floor of a two story house and was built as part of the original house, is fully insulated and has a regular basement.
2. The bathroom was a bump out additon and was built over a crawl space and is also fully insulated , but it has 3 exterior walls,one window and a roof ( which i believe is insulated )
3. The thermostat for the kitchen zone is located about 15' from the
bathroom

Which leads me to my question , How do I get the bathroom the same temp as the kitchen?
DO I.........
A. Rip up the floor and lay down the same size tubing
B. Install a thermostat in the bathroom and put it on a different zone

OR is there another way of getting the temps consistently the same.
Any of your expert adivce would be greately appreciated.
Awesome forum !!!!!!!!!
Billy.

The resistance on the smaller tubing is more than the 1/2", so unless you have a balancing valve, water won't flow as easily through the smaller tubing. IF your manifold has balancing valves, make sure the 5/16" valve is fully opened, and then slowly back off the 1/2" valve a little at a time and let it run for at least a couple of hours to see if it balances out. Eventually, you'll get it so it will be even in both rooms. This may cause the loop to have to run longer since you'd be restricting the flow through the kitchen loop, but it should resolve the difference. The lower the flow, the less heat available, so it needs to run longer. If it gets to the point where you can't keep the kitchen warm, then you'd have to separate them into two zones so you can reopen the loop's flow back to full.

Ideally, each loop is the same length and same size tubing, which makes it easier to balance things, but that rarely is the case.

Thanks Jim fot the great advice ..
I tried it last night and it definetly has increased the temp in the bath.
Would increasing the flow to the bath and restricting the flow to the kitchen make it run inefficiently ?
Billy.

I don't think so. Running the heat constantly offers the most comfort. The only gotcha is if by turning the flow to the kitchen down, it can't keep it warm enough.