How Much Hotter Is An Attic Than Outside

Warner is right that the attic should be close to the outside temp.

How much hotter is an attic than outside. In summer if the attic is hotter than the outside temps it increases the temp in the home and makes the air conditioning work harder. Your insulating and heating cooling the house not the attic. At night outside temperatures have dropped to 70 f but after leaving windows open all night the indoor temperature is still at about 79 f. Now if the ridge vent is only partial or if the attic air temperature is excessive 20 degrees higher than the outside air fans may prove beneficial pick the right fan.

Under side of roof deck is not much warmer than the attic air temperature. The frost is frozen condensation from the warm air meeting the cold air and not ventilating if that. Watson s hunch is there isn t enough attic ventilation. All the heat stored in the insulation filters into the house rather than venting to the outside.

Since attics are often under insulated poorly sealed and poorly ventilated the temperature environment can be drastically different in an attic than in the rest of the home. 105 in the hot summer in the south if outside temp 85 90 35 40 in the dead of winter in the south if outside temp 20 30. This is most notable in the case of attics. Also depends on your humidity roofing etc.

During the summer this leads to the hot air from the attic seeking out the cooler conditioned floors below. Ideal attic temperatures shouldn t be more than 10 to 20 degrees hotter than outside temperatures. If your attic soars above 100 degrees and reaches the 150 mark its time to consult. Here is statistics over the same period of the temperature rh and dewpoint of my unconditioned attic.

Note the average condition 80 5f and less than 47 37 rh this attic makes it into ashrae 55 s comfort zone.