Which type of water heaters should not obtain combustion air from sleeping rooms or bathrooms?

Water heaters that are fuel-fired should not obtain combustion air from sleeping rooms or bathrooms due to safety concerns associated with combustion gases. Fuel-fired water heaters use natural gas, propane, or oil as their energy source, which means they produce combustion gases, including carbon monoxide. If these gases are vented improperly or if there is insufficient air for combustion, there is a risk of them entering the living space, which can pose serious health hazards to occupants.

In contrast, electric water heaters do not produce combustion gases, as they operate using electricity and do not require air for combustion. Hybrid water heaters, which may combine different technologies, typically don't involve combustion processes in the same way. Likewise, solar water heaters generally use solar energy to heat water without combustion, eliminating any associated risks with indoor air quality or safety.

Due to these factors, it's critical to ensure that fuel-fired appliances are installed with proper ventilation and air supply requirements, maintaining safety within sleeping areas and bathrooms.