Being on the farm for years and working with a zillion rusted bolts and nuts, I believe that heating a nut or bolt does not depend so much on the expansion as that heat will loosen the rust that is preventing the bolt or nut from turning. There is a lot of surface area involved with all the threads on a large nut.
The coefficient of expansion for carbon steel is about 6.5 millionths per inch per degree F. For example a 2" shaft would expand about .011 inch in diameter if one heats it from room temperature to a dull red temperature of about 900 degrees F. Unless you use a pyrometer to check the temperatures or know your color changes you may not be heating a steel object as much as one thinks. Unless one has exceeded the elasticity limits of a metal it returns to its normal dimensions upon assuming room temperature.
Interesting how much a 4 ft steel wagon wheel rim will shrink onto the wood wheel after heating the rim in a bed of coals and cooling with water.

Thanks to all for the ideas - found local rental shop that rents 1" impact driver, will go with the 2-1/2" socket I bought. I have a 20 gal 2 cylinder air compressor so will see how that goes.

A small compressor and tank will work fine, provided you have large enough air lines and patience as the tank refills, I find a 1/2" supply line and fittings is sufficient for my uses. If you don't have a good 1/2" or larger air hose, poly pipe works great for occasional use, not suitable for continuous use, but for once in a while if your careful with it, it's fine, very available and cheap, toss a spool of it somewhere it wont get crushed and you always have a long air line for that job that is hard to reach.

Are you certain you are turning in the "proper" direction?

With many stuck/frozen nuts over the years - heat the flat of the nut on two sides, be careful to not heat the "points" as you will deform them and it will become a "Round threaded stuck washer"
I have had luck using a standard cutting tip to help isolate the heat to the flats.
Worst case, split the nut - there are some fantastic cutting blades now from Dremel to large grinders.
Good Luck!

I have enough practice I will just get the fire wrench, wind it up hot and blow through one side of the nut. If you run hot and fast it won't even nick the threads on the bolt - the threads will be perfectly clean. Get it cold and do the other side and the remaining pieces will fall off.

Maybe its metric.........pfffff.

Candle wax! lemon scented [acidic] ??????

If the impact doesn't work, just shave the nut down with a torch till you get close to the threads and then hit it with a hammer. You should be able to find a replacement nut on McMaster for $10 or less.

Got the big nut loose - added 5 ft pipe to end of breaker bar = 7 ft lever, hang a  270# retired truck driver on the end and it let go with a "pop"

Claremontcat wrote:

Got the big nut loose - added 5 ft pipe to end of breaker bar = 7 ft lever, hang a  270# retired truck driver on the end and it let go with a "pop"
 

"That'll do 'Piggy'. That'll do."
Told ya it needed more 'Cow Bell" .
Good deal.