What type of heating source is not acceptable as a sole heat source in a room?

Unvented space heaters are not acceptable as a sole heat source in a room due to concerns about safety and air quality. These heaters operate by burning fuel, which can lead to the production of carbon monoxide and other harmful gases within a closed environment without adequate ventilation. This increases the risk of dangerous gas accumulation, which poses significant health hazards to occupants.

In contrast, electric heaters, gas wall furnaces, and central heating systems generally have safety measures, such as venting or are designed for extended use without contributing to indoor air quality issues. Central heating systems distribute heat more evenly and are designed to handle heating needs across larger spaces, providing consistent and safe warmth. On their own, electric heaters can be safely used for supplementary heating, while gas wall furnaces typically have vented options that ensure proper air exchange.