| Sure, leave the spirovent. They work better on the supply when the water is hottest.
Tee for the tank wherever it's convenient. The tank can be placed somewhere else and a 1/2" pipe run to it. Several feet doesn't matter. (I know of someone who's used a stainless braided dishwasher hose and put the expansion tank on the floor in an old wok ring... but he's a professional.)
BUT, if Raypak suggests a secondary circulator, that would probably be the preferred solution. That would even trump moving the expansion tank so you're pumping away (it's a pumping away day here on DIY -- see some other threads...). But there's no reason not to set up the secondary circulator on the supply side so it's pumping away from the existing expansion tank. (Assuming here that they will allow pumping in series and by 'secondary' they don't mean that you have to pipe the whole system as primary/secondary. Exactly what model boiler is this, anyway?)
The most important thing here is to follow the boiler manufacturer specs. The Raypak, as I interpret the manual (keeping in mind I've never seen a Raypak in person), is a rather different boiler from a plain vanilla hunk of cast iron. They go to great lengths to specify flow rates, and provide a piping/pumping setup that makes the thing work right, and safely.  |