INSERTS ARE CONSIDERED ZONE HEATING TO BRING MAXIMUM EFFICIENCY TO YOUR EXISTING FIREPLACE.

Heat&glow is a premium fireplace brand they invented the direct vent fireplace they offer gas inserts in 30" and 35" sizes 

Heatilator is IS A SISTER COMPANY of heat and glow they are better priced and offer more stripped down gas models with fewer bells and whistles

same sizes 30" and 35" 

regency is a Canadian company which offers multiple size gas inserts. they are a premium brand like heat&glow similar pricing

regency also offers wood inserts as well 

regency wood inserts