The hose coming from the firewall, and the hose coming from the rad. Can I just block them off?

Does coolant pass thru them if i am not using the heater?

 

You can block them. Just make sure its going to the heater core only and not to the beehive cooler. (If you have one.) You can get hose barbs from autoparts store in all sizes and just connect the 2 heater hoses comming from the firewall togeather. Im guessing your heater core is leaking?

 

does the coolant need to circulate if the heater is not being used?

 

Don't forget that if you block off your heater core feed from the radiator (lower hose attach), that you'll also need to block off the heater return on the driver's side of the block, just below the Oil Filter tower.

If you only do one, you're still going to lose coolant once it heats up, and you'll lose it very quickly.

When I had my radiator rodded out and rebuilt last month, I had the shop weld down the heater feed, then installed a plug on the return line. My prior bypass used about 4 feet of heater hose going from the radiator feed all the way along the firewall and back into the return. This was to bypass the heater core inside the car, since my temp control valve was rotten and would spray hot coolant on my right foot in colder months.

Nothing like hot coolant on your right foot to slow you down in traffic! HTH,