I have a small house, no basement, just a crawl space for the furnace, hot water heater, water softener. Would it save me money to open the duct work on the furnace to heat the area, or keep it closed so all the heat goes up to the house?
The short answer is no. Heat belongs above the floor and the insulation, not in the crawlspace where it's just a waste. Worse than that, If you open a return duct too close to the furnace, you can draw deadly carbon monoxide gas into the hosue, which is very dangerous. There is no good reason to heat a crawlspace. Having said that, there is somehtig known as an unvented crawlspace. That is done to minimize moisture, it has nothing to do with heating.