In order for I or someone to offer assistance, please share the following

1. Sq ft of home and description of construction
2. BTUs of furnace (assuming that is all on the tank)
3. KW of heat element
4. High demand times, every night?,. from when to when?

Assuming tank is full, you have up to 2,159,400 potential BTU's in the tank. So a 100,000 BTU input furnace could burn 21.59 hours.

Just guessing, if your furnace is fired for 25 minutes of every hour, over 8 hours you will get about 6-7 days on a tank.

You may wish to reconsider that idea with the costs of filling small tanks, based on above estimations.

Thanks! I'll get all that information this weekend and post it up. According to the electric company's history and recommendations for the upcoming year, I will need about 50 hours of gas for the entire heating season. Also the house will already be warm when the electric heat is interupeted and will only be off for 2 hours at a time on average. I cannot be interupeted for more than 6 hours at a time and the history shows 4 hours as the most. These are the times when I think I'd would need gas back up becuase the house will start to cool off in 4 hours. Even if I had to go through 2-3 100lbs cylinders a winter, I'd much perfer that than a tank in my yard.

you think you prefer it, until you realize the cost difference between filling a portable bottle and a permanent tank. around here to refill a regular 20# bottle is about 20.00. i don't have the exact volume, but i think that is a little under 3 gallons, so it means paying almost 7.00 a gallon! bulk tanks cost under 3.00 a gallon to fill, especially if you lock in or prebuy LP.

also, can you safely transport a filled 100# bottle?

if it bothers you to see the tank, why not get a buried one? then all you have is a little dome sticking out the ground that can easily be hid behind a shrub.

I've never seen nor heard of a baried tank here in MN.

I can't find the information on my furnace. It's an American Standard Freedom 90 single stage. But I can't find the the model number to look up the specs online. Anyone know where the model number is located?

No offence but are you nuts ? you might want to look at
davidandkasie's post. There are 4 gals in a 20 lb. propane tank. That means 20 gals in a 100 lb. When your furnace pulls full load on your 100 pounder it will freeze limiting your 100 ponder to 75 percent untill it thaws out. The 100 pounder is subject to recreational tax. That means it will cost you more to fill your 100 pounder than the ugly tank you don't want in your yard. Lease your tank. When you don't want it anymore they take it away. there is usually a discount on a " bulk tank " fill. Anyway the 100 lb. tank doesn't normally have the discharge size on the regulator to supply the needs of a furnace. In other words your furnace could starve for fuel. What you want to do might work but not recommended. good luck.