I'm sure most of us in the more southern climes don't bother with interior heat, AC would be more of a concern.

I'm in Canada (eh) where it gets pretty brisk at the start and end of the street rod driving season. My question for others in the more northern areas where a heater makes sense: How did you plumb your heater and manifold heat? How does it work? My plan is to run a hose from the water outlet below the thermostat to the manifold, from there to a T in the heater return hose to the water pump. A separate hose from the water outlet would feed the heater, with a shutoff at the core for warm weather. I'm wondering if the common return hose would have enough capacity for both "circuits" to work well enough.

I think you'll find it is more a matter of whether the manifold heat or the car heater works in the colder weather. By tee'ing them together the water will flow through the path of least resistance, most likely the manifold heater and your interior comfort will suffer. If you are attempting to tee them as you describe I would put and adjustable restrictor ( valve ) on the line coming from or going into the manifold heater. Since the manifold will not need anywhere near the volume the cars heater does you should be able to throttle it down to a point where the cars heater is satisfactory for comfort.

i use the keep it simple method run the heater hose to the heater then from the heater to the maifold then to its retrun point. one loop no valving and it looks cleaner.

Bob308, I hear ya about keeping things as simple as possible, do you find constantly circulating coolant through the heater core (no shutoff valve) pumps heat into the car when you don't want it to?

Mike G, the mention of restrictors brings up another question, how much circulation is enough for manifold heat? Usually you see a 5/8" heater hose diverted to heat the manifold. Is that overkill? Would a 3/8" or 1/2" line supply enough heat?

3/8s would way to small to keep the intake heated. I would think the Cold fuel would kill any heat the 3/8s would give. I wouldn't go no less then 1/2 Bu t5/8s would be the better seeing that a heat core runs 3/4 or 5/8s lines. And i beleive it's 3/4 in 5/8s out.

never had a heat problem in the car when the fan was off and the heater vents were closed.

now other things to think about the heater core gives you a littl extra cooling in the summer and closing it off will help the core to clog up.

Thanks for all your replies, gents.
Think I'll go manifold > heater > return and see how it works.