A Christchurch principal says the Ministry of Education needs to better support schools when it comes to air conditioning.

The mercury is rising again in the South Island, with Christchurch peaking at 33 degrees today.

The Ministry says it promotes passive design as the primary approach for ventilation and thermal comfort when designing schools.

Somerfield Te Kura Wairepo principal Denise Torrey says the high temperatures might seem a one-off, but it's a reminder to prepare for the long term.

"If we have got global warming and our temperatures are going to get hotter, our Minitstry needs to ensure that they're supporting schools to ensure our buildings are cool enough in this weather for our children."

Torrey believes the push for sustainably rebuilt schools is at the cost of air conditioning and potentially children's education.

She said kids can't learn in the heat and with Canterbury's hot temperatures and a future of global warming, the stance isn't good enough.

"I understand new builds weren't allowed to put in heat pumps, they were to design their building to be sustainable."

However, fellow Christchurch principal Shane Buckner is happily surprised with how their rebuilt school's putting up with the heat and without air conditioning.

Wairakei Primary School principal Buckner said the buildings are naturally cooled, with large veranda spaces, good insulation and big doors and windows open wide.

"It was actually much nicer coming in the buildings than being outside because there was a marked difference in the temperature."

He said he is impressed with the return on their school-funded solar panels.

Bronwyn Seawood, principal of Windwhistle School, said students need a water bottle, sunhat and cool clothing. 

"Most of them are playing in the shade and making very sensible decisions about staying hydrated."

The Ministry has responded saying it's the Board of Trustees responsibility to ensure the health and safety of students and staff and how they heat or cool their classrooms.