[VAC] Re: Radiant flooring

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxx>]

10,000 btu would be super, a bit big for a Caravel but good for rapid
warm up, probably a hair small for a 33' Excella.

I'm not fully convinced for a meandering radiant heating line that air
alone will move enough water out to make freezing be no problem. I'd
rather have it all drain by gravity with the trailer tipped one way or
the other. Like the book procedure for draining the water system as
originally installed. I'm sure a sloppy repair can mess up that plan and
leave pockets of water that can split a line even with air around it
because the ends might freeze before the middle and keep the water from
pushing lengthwise when freezing.

I see no problems combining water systems to use the water heater as the
boiler for radiant heating system. I plan to do that for a house, in the
plans for most of the last decade. By using 11 inches of wall insulation
and at least 16" of ceiling insulation with double pane windows, I
figure on getting by with about 27,000 BTU that about 8 KW of heating
elements can provide in a larger water heater. I'd probably change the
wiring so both elements would run at the same time. By eliminating the
conventional furnace, I can justify the extra insulation, otherwise
economics for that much insulation don't work out. And with lots of
insulation super efficient furnaces don't work out financially either.

The general objection to using domestic water for the radiant heating
system is that after a while a boiler tends to separate air from the
water and it was the air that would cause corrosion on the metal parts
of the radiant heating system. Using plastic pipe instead of copper, I
think, makes the metal pipe corrosion not a problem. There might a
problem that 120 or 130 degree water may be a hair hot for the wash
basin and shower, but there are inexpensive ($90) thermostatic shower
mixing valves that can handle the entire domestic water needs of a house
and mix that overly warm and some cold water to a safer temperature.
There are much more expensive industrial thermostatic mixers but their
flow rate isn't needed in a house or a trailer. The pressure compensated
shower mixer valve isn't the right one.


Radiant is a technique of heating what needs the heat, not trying to
heat the entire air volume and hoping it warms the floor. That makes it
more energy efficient. Task heating you might call it, analogous to task
lighting. My dad heats his house that way with electric heaters at about
the cost of oil heat. He just heats the spot he's in and since he was 88
last week he doesn't run around so fast.

Gerald J.