Residential Grade fire doors are typically used where a garage meets a house. Residential steel-edge doors can hold a 90-minute fire rating similar to a true commercial door but use a thinner gauge steel. Residential wood-edge doors can hold a 20-minute rating.
While the door itself may hold a higher rating, the rating of the unit is dependent on all of the components used. For example, if a 90-minute rated door is placed in a 20-minute rated frame, the unit can only be rated for 20-minutes or the lowest rated component in the unit.
A fire rating does not necessarily indicate the amount of time a door will withstand a fire. For example, a fire door rated 60 minutes does not guarantee that the door will withstand fire for 60 minutes. The rating means that in a controlled test environment, a brand-new door held up for 60 minutes. However, in a real-world application, other factors like heat intensity could greatly reduce this estimate.