Ka30P wrote:
Hi Rob,

You wrote Do I have to have an opening in the ice for gases to
escape? Should I heat
the bottom of the pond or the surface?

Yes, you are going to want to keep an opening in the ice to keep your
crew alive.
There are floating pond heaters, they come on at a certain
temperature and heat just the area around them.
Or you can run an air pump with a bubbler attached. The agitation
keeps a hole open. (I attached my air pump to the post my electrical
box is on and then covered it with an upside down tub to keep it out
of the elements.)
Some folks disconnect their pump and put it under the surface of the
water and keep the hole open that way.

Energy usage is important. I think the least expensive way is to run
a bubbler but I could be wrong. Anyone know? We have some Canadians
online who can chime in with what they do.

Toronto area, so a tad warmer than Ottawa, okay, much warmer than Ottawa(I
lived in Ottawa 11 years.)

I run a 1250 watt floating pond de-icer, does an excellent job of leaving a
big hole in the ice, and because it is thermostat controlled, switches off
when not needed. I saw no change to my electricity bill running the de-icer
from January until April.

I had used one of the 100 watt de-icers, but they freeze up way too fast if
one gets rain/ice rain followed by freezing temperatures, plus the hole is
mighty small. Found my fish like to come up and hang around the 1250 watter,
so seems to be an added bonus.