[Greenbuilding] Radiant heat boiler/questioning assumptions

[Alan Abrams AIBD]

Hmmm, 144kbtu for a 3 bath house???  On what is this based?  What about
adjusting behavior to the capacity of the system?  I just occupied some
space I remodeled, with a shower that has a single handle valve--it's a
breeze to rinse up, snap off the water, lather up, snap the water on and
rinse--1/3 the water use!  (the only regret is that I didn't insulate the
riser from the valve to the shower head--that nanosecond of cold water is a
start)  The coolest thing I've seen in kitchen remodeling lately is
something a client suggested--a foot valve for the sink faucet.  How many
btus saved, I dunno, but the point is being green may take a little change
here and there in our consumption habits.

-aa
  
Alan Abrams AIBD
Abrams Design Build
a sustainable approach to beautiful space
www.abramsdesignbuild.com

David Seth Melchert wrote:
> We have started a large residential remodel in Orinda, CA. The 2,800 sf 
> house will be heated with radiant floor heat. We were planning to use a 
> Baxi Luna 330 instant heater for combined radiant and domestic hot 
> water. I really love the Baxi Luna for its compact design and simplicity 
> of installation, not to mention its general high efficiency.
>
> However we are concerned about its capacity to serve the demands of a 3 
> bath house. The homeowner consulted with a supplier who suggested that 5 
> gpm, delta 70 degrees is the minimum required, more than the 144,000 
> BTU's the Baxi Luna provides. Baxi has a new Modula supplemental tank 
> that holds 21 gallons and serves as a kind of buffer for temporary high 
> demands. My homeowner is concerned this will not cut it. They are edging 
> towards having separate heat sources, such as a Noritz or an efficient 
> large tank for DHW.
>
> Here are my questions: how many gpm should we figure for hot water needs 
> at any one time, and how often might a family of four run into 
> insufficient hot water using the Baxi? Would you agree that providing 
> separate heat sources for radiant and DHW would be the best path?