Mike wrote:

Having used the Hot Head in a variety of glass and non-glass situations,
if you are getting your gas from the same line as the heater, I would
expect
that the variation in flame is more due to the change in pressure in the
gas
line than the change in atmosphere. In fact, I feel a bit of panic about
your statement because IF the atmosphere is changing that much (to affect
the flame) you are at risk for CO poisoning which would result from
burning
in low oxygen. Please check it out.

It's an electric space fan heater that sits near the door of the shed.

The torch is in a shed outdoors with very adequate ventilation, I think it's
more a case of the draft from the fan being enough to disturb the torch
flame more than anything else. Mike (the other Mike) works with the door of
the shed partly open to allow a run of fresh air all the time and the roof
is vented, but in a Yorkshire winter cold snap, the fan heater was on simply
to keep his feet from freezing. We're looking into a different heat source,
like a sealed oil radiator, no fan, no worries, and just a higher electric
bill but warm feet and no extra air currents.

Thanks for the concern, though. We're very conscious of gas and the
problems with it as we live on a boat that uses propane for the cooker, and
until last year had a gas-powered fridge too.

-Su