Stacking AC voltages

I need 36VAC, I've found 12VAC, 18VAC and 24VAC. I think I can combine a few of these to get my 36VAC (18 + 18 or 24 + 12 = 36) Can I stack (combine) a couple of VAC transformers to get the voltage I want, or will this give me unpredictable / unuseable AC outputs. I need an output of 36VAC to supply a circuit that I purchased.

Just phase them properly, and the max current draw of windings in series is that of the smallest rated 'former.
You can also parallel them to get more current capability by using dropping resistors but this method wastes power.

You can also subtract them too so if you have a 48V transformer and a 12V transformer you can connect them out of phase to get 36V.

All good stuff. Thanks for the replys.

I don't know how to phase them though.

A little help please.

I would assume you would just hook them in series and measure the voltage. If you hook a 24V and a 12V in series and you only measure 12V on the output, you probably have one of them backwards.