Ron Rosenfeld writes:

Obviously, any resistive load will heat up if you put DC voltage to it.

But now you've got me thinking.

What are the design considerations for converting a heating element that
has been designed to function on 120VAC to 12VDC?

Note that I wasn't suggesting using 12VDC. I was thinking in terms of
an equivalent voltage DC. That would not require any changes to your
installed system.

I'm really not even suggesting using DC; I was just pointing out that
the heating elements can handle it. Nine 12V batteries in series should
give approximately the equivalent power to a resistive load as 120VAC.
It could be done but it'd be a pain.

I think you'd be happier using a special-purpose (cheap,
high-efficiency) inverter on a single 12V battery. You could have a
noisy 400 Hz inverter and it would be perfectly fine for your heating
elements.

....or you could just buy a decent general-purpose inverter and use it
for powering a video projector for late-night drive-in movies at the
hangar when the weather is nice.

--kyler