The G and K series machines have a much more efficient heater and can cook you out of the cab.
I assume you have a C or F series. In the older C and F series the heater works, just not very well. The "H" fitting is stock.
I asked a Bobcat mechanic about the poor performance of the heater. He asked me if I could feel a restrictor inside the crossover hose in the middle of the "H" . If you remove the restrictor the coolant takes the path of least resistance flows out of the engine, through the crossover tube and right back into the engine. He stated they have seen many machines with the restrictor removed by someone thinking it would help.
Does your heater core get hot? If your pinch the crossover hose does the heater core get hotter? If not, you could have a plugged heater core or possibly the core is full of air and needs to be bled.
I was concerned about the poor performance of my heater when I bought mine. (Mine is missing the restrictor.) I thought about removing the "H" section all together or putting in a valve so I could control the amount of coolant going to the heater. I also thought about removing the front cover of the heater to see exactly what the temperature knob on the top of the heater actually controlled. Shortly after I realized that don't spend enough time in the cab at any stretch and I am wearing full winter clothing. With the door on, I just ended up fogging up the windows. Now I just leave the door off and don't even use the heater. The only time I miss the door is when I'm using the snowblower attachment and the wind is blowing...
