Tommy Canuck

I am a newbie to cycling,only been riding since July. Am up to a 35 mile loop in just over 2 hours, so for a 45 year old guy, I was fairly happy with my progress. I have a stairmaster and a treadmill but since my new affair with cycling, I decided to buy a spin cycle for the long cold Canadian winter. A local club around here is closing down and my buddy managers it. He put us each aside a Schwinn Spin Cycle and I am going to buy one for home. Today I went over to the club at lunch and rode the spin cycle for 40 minutes. I could not beleive how wastewd I was after 40 minutes on this thing. I felt more exhausted that I do after 2 hours outside on the bike. I was totally baked and was sweating like a first time ******.
I trhink I need to get a heart rate monitor to see what I was doing to myself. In general is "spincycling" considered a good workout in the off season. It felt very similar to the bike but I just seemed to really tire out fast, not sure I could have even done an hour on it. I am going to try again tomorrow but this thing really put the boots to me.
Anybody else use a spin cycle as oppsoed to a trainer? What are your opinions on it?