I am going to disconnect my heater core here in a bit and I wanted to know the size of pipe to buy.

Also, will copper pipe be ok? I figure it is the best plumbing around and won't hurt the coolant system.

Any suggestion?

 

Why disconnect the heater core? Even if it doesn't get cold enough to need full heat, you will still find situations where heat is needed.

A humid rainy day for example. The heat is benificial in clearing the windows much faster then cold air.

If you still want to disconnect then copper pipe is a bad choice. The chemicals in the coolant will react with the copper and cause it to corrode from the inside and eventually fail. Aluminum pipe is a better choice. The best thing to do is to run a length of heater hose between the fittings coming off the engine.

 

Remember, the newer vehicles have quick disconnect fittings on the ends of the hoses that attach to the heater core connections.