To control heat it is easier, cheaper, better, to do it with the air
vents on top. Dole makes a 1-10 adjustable, Gorton have different
letter sizes, forget the hadrware store made in china ones they are
restrictive and dont last, they equal maybe 2 on a Dole adjustable.
Changing a valve to control heat will cost alot more, take more time and
not be as accurate in balancing temps. A leaking valve can be repacked.