I just had my heat pump replaced (Lennox) which is used in combination with my oil furnace. Here's the issue.
When ny heat pump goes into defrost mode, the oil furnace kicks in for 30 seconds then shuts off and I feel cold air from the registers for a couple of minutes or I would guess until the defrost cycle is complete on the heat pump. This happens perhaps once every 2-3 hours. Is it ok for the oil furnace to kick in several times a day for 30 seconds and then blow out? Is it possible that the defrost cycle time on the HP is only 30 seconds? I live in Montreal so hence our cold climate.