I'm planning to install the thick, "swimming pool" vapor barrier in my crawl space and have foam sprayed on the block walls to insulate the space. The spray insulation guy said I needed to have my forced air hvac system condition the entire space, so I guess I need to cut some vents from the heating ducts, but am concerned about returning the air from crawl space back into the house. If the barrier is installed well and everything else is sealed and insulated well, do I have anything to worry about? The concept of thinking about a heated crawl space as "a small basement" makes a lot of sense to me, but I'm still just a little worried about returning air back into the house.
not really. that's what i call a poor mans crawl space dehumidifier lol that's what i did at my dads house. i covered the earth with 12mil plastice, and sealed the vents. i didn't insulate the walls, and i use an 8x8 return that i fabricated myself, and i have 4x6 supply. nice and cozy down there summer and winter
R408.3 Unvented crawl space. Ventilation openings in under-floor spaces specified in Sections R408.1 and R408.2 shall not be required where:
1. Exposed earth is covered with a continuous vapor retarder. Joints of the vapor retarder shall overlap by 6 inches (152 mm) and shall be sealed or taped. The edges of the vapor retarder shall extend at least 6 inches (152 mm) up the stem wall and shall be attached and sealed to the stem wall; and
2. One of the following is provided for the under-floor space:
2.1. Continuously operated mechanical exhaust ventilation at a rate equal to 1 cfm (0.47 L/s) for each 50 ft2 (4.7 m2) of crawlspace floor area, including an air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2.8;
2.2. Conditioned air supply sized to deliver at a rate equal to 1 cfm (0.47 L/s) for each 50 ft2 (4.7 m2) of under-floor area, including a return air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2.8;
2.3. Plenum complying with Section M1601.4, if under-floor space is used as a plenum.