[Greenbuilding] Radiant heat boiler

[David Seth Melchert]

Thank you to all who offered such a well-considered response to my query 
yesterday.

A few clarifications:

The home owner already nixed solar hot water panels - it was my first 
suggestion a year ago when we first started planning. Most of the house 
is shaded by a grove of redwoods.

I mis-stated the BTU's of the Baxi. Its input is 126K BTU.

GFX/Power Pipe is not really a possibility due to a whole number of 
logistical/engineering reasons I won't elaborate here.

Many of you suggested I help the owners change their habits. This is a 
tricky issue - those of us on this list are quite enthusiastic about 
changing our behavior, but many (I would venture most) Americans are 
more convenience and results driven (didn't Amory Lovins state, 
"Americans don't care if their power comes from nuclear or solar, they 
just want cold beer and hot showers").

The Baxi 310 is 85% efficient, but the Baxi  HT 330 is a condensing unit 
and runs in the mid 90's I believe.

Yes, George, the floors are to be well - insulated for radiant heat. The 
remodeled house design is carefully crafted for a whole number 
Architectural characteristics. Hot air duct pathways prove challenging 
in places where feeder pipes for the radiant are easy to distribute. And 
they chose the radiant largely for the comfort they experience with it.

The homeowner is not likely to try a new boiler system that not even the 
employees at HSC have heard of. Who knows how they hold up, how well the 
company provides service, etc. But I do look forward to seeing how the 
Phoenix Combi does over time.

One of the first suggestions posted was to have an indirect tank for DHW 
that is heated by the Baxi. This is probably what we will do - replace 
the 21 gallon Baxi modula with a well-insulated 80 gallon tank. It 
obviates the considerable cost of a secondary system. This will also 
provide future capacity for solar panel feed in the future.

I admire the considerable expertise represented by this group. Thank you 
for chiming in.

Seth Melchert
Oakland CA

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?
>
> Thanks
>
> Seth Melchert
> Oakland CA
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