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Viessmann & Siggy differ on efficiency at high return temp?
It's very unlikely I can use in-floor radiant in my home bec. crawl is too low clearance to work safely and ceiling is near code min. So I'm sizing alternative emitters, and that depends on return temp. Can live with ~87% but if I'm paying for a mod con why not see if we can still con with radiators or what have you.
Conventional wisdom seems to keep return temps as low as poss for efficiency (and other reasons). For example, Siegenthaler 3rd ed p78 showing curves for a "representative" mod con indicates barely condensing at 125F, even at low fire. And at high fire, maxing out at hardly better than 90% in any case.
But Viessmann eg 222-F manual p3 indicates 95%+ with return temp of 158F at a 30% load. (222-F modulates down to under 20% where I imagine it's even more eficient.) Even at 50% load it seems to be doing some condensing.
Viessmann stipulates 20F drop in emitters - is that a gotcha?
I don't see similar info for Loch or TT, wonder about that.
Viessmann installers in SF Bay area, feel free to contact me via my profile page re whole house remodel