Grate heater

From simple to ornate, they can contribute significantly to the overall comfort of a room and potentially to a whole house.

[2] This in turn will reduce the amount of firewood needed to achieve the same comfort level, potentially reducing heating costs and expenses.

They work by having naturally convected and forced air funneled into the metal heat exchanger tubing that is then heated by the coals and/or fire.

The ideal tubular grate heater would be built like an ideal heat exchanger with as large a surface area as possible with material suitable to minimize the heaters thermal deterioration yet provide good thermal conductivity with a high airflow rate, similar to your home furnace.

However the unique environment of a fireplace and the burning of gas, wood, coal, pellets, etc., require specific heater designs and material construction making few, if any, grate heaters compatible with all fuels.

This tubular fireplace grate heater has a large surface area heat exchanger in a compact design, with a fan or blower (fans and blowers are not the same) to multiply the effect of natural convection.
This is a very basic tubular blower that sits under a grate and heats the air being pumped through it from the heat of the coals. It has a high rate of airflow but a small surface area.
This is a large and powerful grate heater system that incorporates a large, thermally-conductive heating design along with a multi-blower, high-CFM, forced-air delivery system
Another example of a large and powerful grate heater system that incorporate a large, thermally-conductive heating design and a single-blower, high-CFM, forced-air delivery system