Trace Curry wrote in message ...
What's the best method for using water to store heat to be released
during the night to keep a cold frame from going below freezing?

I was thinking a bunch of those black balloons that you often see at
people's 40th birthday party - filled with water of course.

Any better ideas?

I got one of those Gro-quick heating cables, but it doesn't seem to be
doing much as far as heat production, maybe because it's only 15
degrees?


The heating cable will give you a few tens of watts, and that is just
not enough. Black balloons is a very good idea (they will absorb of
order 100W on a sunny winter day, and give it back at night), but keep
in mind that they will probably only keep the temperature above 27 or
28 degrees. They give back heat through conductivity, which is
proportional to the temperature difference, so they give little heat
until there is a difference of several degrees between water and air.
27 degrees is fine for lettuce or cabbage seedlings, after a bit of
pre-hardening. For the tomatoes, you may have to wait.