Frequently Asked Questions
What is HTHV?
High Temperature Heating and Ventilation (HTHV) is a direct-fired, 100% outside air technology used to heat new construction and retrofit projects.
What is an 80/20 unit?
An 80/20 unit is a recirculating direct-fired heater. Like HTHV, it has been used for heating in new construction and retrofit projects across the US.
What is the main difference between the two for indoor air quality?
The difference is the amount of pollutants, measured in parts per million (PPM). HTHV is the clear winner on IAQ. The infographic above compares the PPM levels of each technology against the acceptable limits in the US and Canada.
What does OSHA consider good IAQ?
OSHA says good IAQ includes comfortable temperature and humidity, an adequate supply of fresh outdoor air, and control of pollutants from inside and outside the building.
Who sets the acceptable pollutant limits for workplaces?
Both OSHA and the Canadian Standards Association (CSA) set limits on acceptable PPM levels for different pollutants in working environments.
Which performance and safety standards apply to each technology?
ANSI Z83.4 covers 100% outside air, non-recirculating, direct gas-fired industrial air heaters such as HTHV. ANSI Z83.18 covers recirculating direct gas-fired industrial air heaters, which are the 80/20 units.