How to Size Copper Tees for Hydronic Heating Systems

Tees are generally measured from the "Run" to the "Bull".

The "Run" is the left-to-right or the length of the Tee.

The "Bull" is the top part of the Tee.

For example if a Tee is 3/4" X 3/4" X 1/2", then the left inside diameter is 3/4", the right inside diameter is 3/4" and the top inside diameter part is 1/2". Tees where the run and the bull are not uniform are referred to as "Reducing Tees".