[Cob] Re: pipes

[Amanda Peck]

On-demand water heaters are notorious for wanting water pressure.  The specs 
mostly say that the minimum is 20 psi, but I've gotten the impression that 
hot water is a bit iffy when the pressure is that low.

Solar hot water is probably the least awful for people with low pressure.  
Especially if you can do it yourself, get old solar panels from the Carter 
years (frequently free for getting them off somebody's roof!), weld, or get 
someone to weld, a heat exchanger, and a tiny solar pump to push the 
propylene glycol through it.

Or, there's a Coleman heater that heats "up to" 40 gallons with a pound of 
propane and a rechargable battery pump, might even push the water up to an 
overhead tank.  (also, probably not at the same time, heat water to 140 
degrees)

http://www.ebizenterprise.com/index.asp?PageAction=VIEWPROD&ProdID=39337
..............

Barbara wrote:

Check on your water pressure before embarking on a pex project or any
plumbing with an on-demand water heater.  Our pressure is fairly low and we
have conventionally sized pex runs (larger for washer, smaller for
sink/toilet/tub) which do not work well with the combo of mixing valves and
the instant-on heater.  It's gotten worse over three years as our water is
heavily mineralized, as well, so now, to get hot water at any tap other than
the washer, we have to turn another tap on to a trickle so there is plenty
of volume running through the on-demand heater.  We understand we can
correct the extremely wasteful problem either by replacing the on-demand
heater with a conventional one; putting in a pre$$sure tank; or replacing
the valves with non-mixing types (a line to a faucet for hot, and a line to
faucet for cold).  Although it's the most costly option, we will probably
opt for the pressure system so we'll have sufficient pressure to run a drip
system for the orchard and gardens.  We worked with a plumber, but our pex
installation was his first.  Also, the local plumbing store loaned us the
pex tools since they're pretty pricey and Home Despot wants to sell you the
materials and the tools.

Barbara