DHW coil recovery rate?

Hello,

I haven't posted here in a while, but would like to thank the forum for all the info that was provided when I built my chimney and installed my Energy King 480EK furnace 3 years ago. I am planning on installing a water coil in my Energy King 480EK this month. The coil is 24" long by 7" and will be hooked up to a 40 gallon storage tank and circulation will be through thermosiphon. Does anybody know roughly what the recovery rate would be for this setup? The reason I ask, the used storage tank I bought came with a circulation pump and wasn't sure if there is an advantage in using it.

Thanks,
Dave