Aftermarket heater question

Removing the stock heater to make room for upgrades and will be replacing w/ one of the Summit Moab heaters. Is the 28K BTU unit too much for my climate zone (OK-TX)? Will the 12K BTU unit be sufficient? There's not much price difference so comfort is my only thought.:v6:

 

Go with the bigger one, you can always adjust the heat down with the temp control.

 

I've found too much heater to be as uncomfortable as too little. These units appear to be internal air only (like Max on new car settings). If there was a way to blend air, big wouldn't matter. In this case, I'm not so sure. There's a big difference in the two units.:v6:

 

The inlet on the Summit 28K unit is round, so there is no reason you couldn't pull in fresh air - it would just take some creative work with ducting. Also, I think you could put a valve on the coolant inlet and meter the hot coolant to get cooler/warmer temps. The fan on the unit is a three speed (Hi, Med, Low).