single tank solar?

Royboy

about single tank solar water heaters?

I've never done one - always used a solar preheat tank feeding a conventional water heater - either tank or tankless.

I've got a small new house to put a solar water heater on and also do a conventional heating system feeding a radiant slab. owners are not around for significant parts of the winter and so I'm thinking it makes sense to route the solar energy into low-temp maintenance heating when they aren't home. which has led me to the idea of a Phoenix water heater providing hot water and space heat via a loop w/flat plate HX. with the low system temps for hot water & radiant slab, should run in condensing mode pretty much all the time.

so there's the regular Phoenix, which if it was already in, I'd feed from a solar preheat tank - my usual style. but since its new construction, there's the option of a solar Phoenix - which has the solar HX in the bottom of the tank and the gas fired HX halfway up in the tank.

the simplicity of one tank for spaceheat and hot water with solar input definitely appeals to me. I don't like having the effective volume of solar storage reduced by having the conventional heat halfway up the tank (in my mind this means there's only 40 gals - more or less) of solar storage in the 80 gallon tank. I suppose I could go with the larger Phoenix (120 gal). haven't priced any of them yet but I'm guessing that wouldn't be real cheap.

any thoughts about how you'd approach this, thinking about mechanical elegance as well as cost effectiveness ... ?

or about single tank solar, in general ... pros & cons

Roy