About 100 guests were told to leave the Holiday Inn Express on Paterson Plank Road in Carlstadt just after 10:30 p.m.
They were put on buses and taken to other hotels.
One woman had a slight headache, a symptom of carbon monoxide exposure, and taken to the hospital for treatment.
Firefighters arrived to multiple carbon monoxide detectors going off on multiple floors.
The carbon monoxide rate was 180 parts per million. Rates of 100 ppm or greater can be dangerous to human health.
The leak was traced to a blockage in the venting system for the pool heater.
The blockage was removed and the hotel was ventilated to bring down the carbon monoxide levels.
Firefighters said guests of the hotel were cold and upset, but most were not injured.