Hot days and heating days
NOAA's U.S. climate normals for Manhattan Municipal Airport give 5104.3 heating degree days and 1489.9 cooling degree days in a normal year. The same NOAA normals count about 58.0 days a year with a high of 90°F or more at Manhattan Municipal Airport. Both figures are from NOAA's 1991-2020 normals.
The day count is the number of days when the high reaches 90°F or more. The degree days describe how much heating and cooling a building needs over a normal year. For painting, one is about the outdoor work on hot days, and the other is about the months when houses are closed up and heated, which is when interior work tends to fill a painter's calendar.
What a hot day does to fresh paint
Paint dries by losing its water or solvent. In hot air, and especially on a surface baking in direct sun, that happens fast. The trouble starts when the paint dries before the painter can blend the next stroke into it:
- Lap marks. Stripes where wet paint overlaps a section that has already begun to dry.
- Brush and roller marks. Paint doesn't have time to level out.
- Poor adhesion and blistering. A skin forms on top while the paint underneath is still wet.
Most paint labels give a maximum as well as a minimum temperature, for the air and for the surface. A dark wall in full sun can be much hotter than the air.
Chasing the shade
On hot days, experienced exterior crews follow the shade around the house: the west side in the morning, the east side in the afternoon. They start early, keep a wet edge by painting full boards end to end, and stop before a wall turns into an oven. Ask your painter how they plan the day when a hot stretch is forecast.
Stain and hot wood
Decks and fences take stain best when the wood is dry but not hot. Stain applied to a sun-baked deck can flash and leave lap marks you can't fix without stripping. Our deck and fence staining page covers timing and products.
Inside during the heating season
The heating months are when interior painting often fits best: rooms can be kept at an even temperature, and exterior crews move inside. A few things to think about:
- Ventilation. Windows may be shut; ask how fresh air will be brought in.
- Dry air. Heated indoor air can be very dry, which speeds drying. Painters adjust by working smaller sections.
- Living around the work. Agree which rooms are out of use each day. See interior painting.
Older paint, inside or out
Under EPA's Renovation, Repair and Painting Rule, anyone paid to do work that disturbs paint in homes, childcare facilities and preschools built before 1978 must hold RRP certification, firms included, even sole proprietorships, and their workers must be trained in lead-safe work practices. If your home was built before 1978, ask how sanding and scraping will be contained and cleaned up, whether the job is in summer or winter. You may also ask whether the firm holds RRP certification.
Questions for a hot-weather job
- What time will you start and stop on a hot day?
- Which side of the house will you paint first?
- What do the label's temperature limits say for this product?
- How will you keep a wet edge on long walls?
- If it's too hot, what happens to the schedule?