How can I heat a crawl space to work in
What is your house heat? If it's some sort of hot air furnace, you might be able to tap it?
Otherwise there are &quot;construction heaters&quot; you can rent which include indirect fire (no fumes) hot air units, with ducts and blowers. But probably more than you want to spend...
Thirdly, unless firstly, as it's simplest and least expensive and most portable:  insulated coveralls and rechargeable heated underwear (if needed. Decent polypropylene thermal underwear will get you a long ways without batteries, particularly with &quot;major brand workwear&quot; thermal coveralls on top.)