The right way to connect a heater?

[simmitc]

So we all know that the later cars have a heater with two rubber tubes coming through the bulkhead: One goes to the heater tap and one goes to a painted-black-copper-tube that leads to the radiator bottom hose. But which goes where?

Now before you all rush with words of wisdom plus doubts that someone like me who has owned Minors for over 20 years wouldn't know the answer, and helpful hints like "the heater works either way", please note that this is just a curiosity.

Theory (a) says that the feed from the tap should go to the top of the heater - as with the radiator, the hot water enters at the top and cools to the bottom.

Theory (b) says that the feed from the tap should go to the bottom of the heater in order to help expel air locks.

I've seen cars done both ways. In the published books there are photographs of it done both ways. Last year I thought I'd check with the concours guys - they were divided about 50% each way, yet nobody seemed to lose any points for not doing it right.

So there we are, just for fun, what does everyone else think ?

[rayofleamington]

to help reduced trapped air it might be best to have the inlet water enter the bottom. That way air bubbles can go with the flow.
For the heater efficiency I doubt it matters (unlike with the radiator, where convection is used to ensure cold water returns to the block)

[Willie]

I have just converted to the late type Minor heater and fitted
it according to the official Workshop Manual. This shows that the
pipe from the valve on the rear of the cylinder head should
go through the bulkhead via the BOTTOM hole and should
connect to the BOTTOM pipe on the heater. Obviously then
the return pipe is connected to the top heater pipe and emerges
through the top bulkhead hole and then down to the radiator bottom
hose.

[MrA.Series]

Yes, that is how everyone I've asked has said it originally came like.