Patio heater

A patio heater (also called a mushroom or umbrella heater) is a radiant heating appliance for generating thermal radiation for outdoor use.

A burner on top of a post, burns liquefied petroleum gas (LPG), propane or butane, and directs the flames against a perforated metal screen. Heat is radiated from the surface of the screen in a circular pattern around the appliance. A reflector atop the burner reflects heat that would be otherwise lost upwards. This is because the reflecting hood is usually silvered which makes it a poor absorber/emitter of heat but excellent at reflecting infra-red radiation back. This reduces the amount of heat lost by conduction as silvered surfaces will not absorb infra-red light. The chimenea is an alternative to the patio heater for home use, which burns wood instead of gas.

Some newer types of patio heaters are electrically powered radiative heaters that emit infrared energy onto nearby surfaces, which in turn heat up the surrounding air.

Patio heaters have become popular with bars and restaurants since they extend the day and the season for their customers to sit outdoors. This increase in the popularity of the patio heater has led to concerns over their environmental effects. One patio heater can produce four tons of carbon dioxide annually.

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Wikipedia