hi.... need some help on sizing a 1998 cabin - 960 sft with cathedral ceilings (entire place) and a 5' deep crawl space. there are 11- 3'X5' windows, 3- 1.5'X5' windows, 1- 3'X4' window, 1-1'X5' window ( all low E/argon filled) and 3 skylights. walls are 6" and the ceiling has 12" insulation. 36" front door all glass and a 36" steel door to the garage.

i have two estimates. one says i need a 3 ton unit and the other specifies a 2 ton unit, both indicate a 2 stage system. it is currently forced air. how can i figure out which is the right one?

also what are the benefits of keeping my propane furnace intact as a backup? we have real winters with below zero readings for a week at a time. will i end up with electric heat during the winter if i abandon the propane furnace? i am getting mixed answers on this.

the soil is dirty sand for about 25' followed by limestone then shale and back to limestone. the backyard is a cedar swamp.

i would appreciate any help.
thanks
zey

The desire is always to pick the less expensive alternative, but I suggest folks get a third opininion to break the tie when 2 don't agree. There are reasons and strategies that could make both bidders correct. You may buy load software for 1 time use or for keeps. You may also have a BTU value offered you already by your contractors which would help us advise you.
Usage of the cabin in the winter would have an impact on design as would size of the lot.
Don't be afraid of electric heat, it is quickly becoming less scary than propane.
Good Luck,
Joe

Your load can vary greatly depending on the infiltration, or leakiness, of the structure. What type of insulation is in the walls and ceiling? Where are you located?

As far as benefits of keeping the propane systems, the biggest benefit I see is that propane can blow up your house. Oh, or it could cause carbon monoxide poisoning. In other words, get rid of it. It's pricey gas, and electricity is safer. Sure electrical problems can cause house fires, too, but you're not going to get rid of it. Why add the propane factor?