james wrote:
I need to work in my crawlspace for a few hours (sealing ducts, etc).

Due to dust, I use a goggle and a dust mask. However, after a few
minutes the goggle starts to fog up, my face gets hot and wet and I feel
like I'm running out of air. I tried different types of dust masks (with
valves and without) but they all gets hot and are hard to breath after a
few minutes. Inevitably, I had to remove the goggle and dust mask.

Is there an combination goggle/dust mask that is actively ventilated,
i.e. a battery powered fan that draws air, to prevent fogging and
moisture build-up?

A supplied-air respirator? Probably be cheaper to hire the work out.
Goggles/mask that suck in local air would just slam the dust you are
trying to avoid, right into your eyes, or the filter would clog up in
minutes.

Have you tried ventilating the crawlspace while you work? Something
similar to what Ma Bell uses for confined-space work in underground
vaults- a big portable fan and/or air scrubber with collapsible ducts
you run down into the work area? I imagine a rental place that caters
to industry rather than DIY would have them. I only have trouble with
goggles fogging up where there is no air circulation and/or high
humidity. (Like working under a car in summer, when it is muggy and
hot.) Of course, I also wear glasses, so that is an extra 2 surfaces
over each eye to fog up.

If an expensive rental is a little off-putting, try the poor man
solution- a box fan and some plastic on the access cubby, sucking OUT,
and some sort of air hole at the far end, for 24 hours or so. If you
don't have plastic over the dirt, sounds like you need it.

--
aem sends...