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You could also research Climate Change and have material available on other topics, but that's not really the point here. Your primary goal is to help people SAVE MONEY on the heating and AC, the environmental benefits are just a bonus.
Then you set a date for when you want to host your party. Try to pick a day most people don't work, they're not on holiday or vacation and they should be able to make the effort to come to your party.
Next you start calling all your friends, co-workers and colleagues at home or at work on the business phones. Basically you want to invite everyone you know, including your local Toronto dentist (or wherever you happen to live). Don't bother inviting anyone who doesn't own a house or land. Apartment and condo-ites have no need for geothermal because they can't install it anyway.
Follow up with emails, Facebook and whatever other means you have available. Don't forget to remind people of the event a day or two before the actual event. (Some people need reminding otherwise they might forget and spend the day indoors watching reruns.)
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You could also hire someone to help plan the party for you. Toronto party rentals/events are pretty cheap/easy to organize, especially if you outsource some of the planning required. Most large cities have party planning companies with the experience and know-how to get the job done properly.
You can also get guest speakers, make a speech yourself, hire musicians and make a huge effort of it. If you invite representatives from local geothermal installation companies they can probably do a lot of the work for you.