“热天”常见的英文表达是 “hot day” 。例如：
It's such a hot day today. I'd rather stay at home.（今天真是个热天。我宁愿待在家里。）
此外，根据具体语境，“热天” 也可用其他表达，如：
sweltering day（强调酷热难耐的天气）
We had a sweltering day yesterday, and I didn't want to go out.（昨天天气酷热，我不想出门。）
scorching day（侧重于温度极高，像被炙烤一样）
It was a scorching day, and the pavement was almost too hot to walk on.（那天天气酷热，人行道热得几乎没法走。）