Cohousing-L Mailing List: Do We need a furnace? & Hot Water heaters

[George Krasle (gskrasle]

HeidyNY,

I went through the process of installing hydronic heat for a greenhouse, and 
there are some (many) details and concerns that are not obvious. I wrote up 
the details of the design to explain them when I wanted to move the plants 
to Songaia, as had been promised as a condition of my joining, but was not 
allowed to do so.

There are regulatory issues. I was not allowed to use a heater not certified 
for the use ('don't know why).

You cannot use one simple heater for tap water and for hydronic heat: the 
concern is that if the water is not circulated for some time, Legionella 
(Legionnaire's Disease) bacteria can grow in the pipes, and 
leaching/corrosion can contaminate the water. For the same reason, you need 
a backflow preventer valve to isolate the secondary water, and therefore a 
separate expansion tank. A pressure regulator/reducer/flow limiter is 
security against disaster. A gas separator would be useful, or a bleed valve 
at the top of the system, to purge air and gases evolved from corrosion and 
such. I would recommend a pressure gauge too.


You should not use copper pipes, at least not cast into a slab, as standing 
(anaerobic) water will eventually corrode through them, a disaster.


I ended-up with a "combi-core" heater, which has a long tube inside a 
regular tank that acts as a heat exchanger, and is made for this purpose. It 
is MUCH more expensive than two separate tanks, I found, and the long 
small-bore exchanger tube requires a beefy pump to push the water through.

I wanted the heat system to be proof against power outages (very valuable 
plant collection), and that part was easy: a 12 V pump made for drinking 
water, hot or cold, pressurized source or not, sold for RV use. A marine 
battery and marine charger, and it would run for at least a week without 
line power. The high head required for the combi-core heater made it hard to 
find a powerful enough pump. These pumps come with a pressure switch 
intended to turn them on when an open tap reduces the pressure, but this can 
be used as a "charge lost/system leak" alarm too.

What I am getting at is that an installer familiar with the technology 
should be consulted; there is much more that is not obvious, and amateur 
installations are giving the technology a bad name when they fail. The name 
"radiant heat" is also not helpful, leading some people to installl it in 
ceilings, where it is not effective. It works by convection, heat rising, 
not radiation. I think the name comes from the "radiators" so familiar in 
city buildings with "steam heat" (which is actually almost the same thing).

George

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