[Greenbuilding] Radiant heat boiler

[Drew A. Gillett P.E.]

ah hah-- the tanked tankless

i would respectfully suggest that the money wasted o a second system to be 
used very in frequently would be much better spent o a solar domestic water 
syste.  these invariably have a tank for storage of the solar heated water. 
this can then be fed to your boiler ( the instantaneous hot water heater for 
topping up and being sent oteither the radiant floor or the showers.

i find adding an electricelement (largest utility willl let you i.e. 6kw to 
the top of the solar tank provides an additional source of energy for use in 
summer so you can leave the boiler completely off and in winter as an 
additonal 20000 btuh .  the solar tank also provides the equivalent of the 
21 gallon tank when you use the top of it withthe electric element in this 
manner.

given the recent doubling of gas and oil prices, electricity's small 
increases look goood as well.  further, more and more lectricity is being 
produced from renewewable sources.

lastly, your owners might consider staggering the showers. it amazes me the 
amount of money americans will spend to avoid a  small amount of wait time. 
sheer ludicrousy
----- Original Message ----- 
From: "David Seth Melchert" <dmelchert at earthlink.net>
To: "Greenbuilder list" <greenbuilding at listserv.repp.org>
Sent: Tuesday, February 06, 2007 7:04 PM
Subject: [Greenbuilding] Radiant heat boiler


> 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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