"Jim" nospam@wherever wrote in
el:

I don't
know weather to use heat tape on these three inch lines or just wrap
with insulation....

Heat trace can melt plastic pipe unless you use the lowest wattage tape.
Problem is the pipe is exposed to very cold moving air which is a much
worse case than buried pipe which sees only a few degrees below freezing.
If you use enough heat trace in a high enough wattage and with tight
wraps to gain a positive heat balance when it is minus 40 degrees that
would melt the pipe when it was only minus 10 degrees and the heat trace
came on.

The wattage of heat removed by minus 40 air in a strong wind can not be
handled safely with heat trace alone. You could use a low wattage tape, 4
to 7 watts per foot, plus wrap the pipe with insulation that is approved
for use with heat trace. Install the heat trace only in a straight line
or you can cause over-heating in warmer weather.

Best solution may be to insulate the whole run of pipe that is exposed to
cold air - even the pipe inside the house. Purpose is to keep as much
heat in the condensate as possible until it reaches the cold end section.
Then there may be enough heat left in the condensate to prevent freezing
and allow drainage between furnace cycles.

If you need a quick solution - heat trace only the section of pipe above
the roof and cover with a water-proof insulation that is approved for use
with heat trace. Use 2 inches thick insulation. Safest method is to use
only a sraight line installation for the heat trace but you may get away
with a wide wrap - coils at least a hand-width apart. If you can't find a
short enough heat trace, then start with the plug end at the roof and
work your way up. Carefully feed the excess heat trace down the inside of
the pipe avoiding any curls. Cover the insulation with something to
prevent UV from destroying it.

Heat trace usually has a builtin thermostat set at 40 degrees F. Make
sure the type you buy does.

Making a safe water-proof electrical connection on the roof under snow is
beyond me. I'd find a way to put the plug through the roof so it could be
plugged in under dry condtions. Staple the plug wire to the uphill sideof
the hole so any water leaking does not flow along the wire to the plug.