Outdoor fireplace specs?

There is a ratio for flue size to hearth size, height above the fire needs to be taken into account as well as the width and depth, this extract is from homebuilding.co.uk website Know your chimneys There are other sources, somewhere I have a print copy from an article in the British Artists Blacksmiths Asosciation magazine about thirty years old. I woud suggest you do some research before you start work.

The Ratio Problem
For an open fireplace to function properly and for the chimney to draw, the ratio between the chimney and fireplace needs to be exactly right. Flues above 6m tall should generally be not less than 1/7th to 1/8th of the area of the fireplace opening, e.g. a 225 mm (9") diameter flue will support a fireplace opening up to about 550 x 550 mm (22" x 22") (see Building Regulations J 2.2.) For bungalows, the ratio should be reduced to 1/6th. A major advantage of precast fire chest and chimney flue systems is that the ratios have been carefully worked out and so are guaranteed to function properly.

If you are building a new chimney, take note at what works for the surrounding properties. They will already have been built or adapted for the local environment.

Replies

Fenlandphil November 19, 2010 at 12:53am

There is a ratio for flue size to hearth size, height above the fire needs to be taken into account as well as the width and depth, this extract is from homebuilding.co.uk website Know your chimneys There are other sources, somewhere I have a print copy from an article in the British Artists Blacksmiths Asosciation magazine about thirty years old. I woud suggest you do some research before you start work.

The Ratio Problem
For an open fireplace to function properly and for the chimney to draw, the ratio between the chimney and fireplace needs to be exactly right. Flues above 6m tall should generally be not less than 1/7th to 1/8th of the area of the fireplace opening, e.g. a 225 mm (9") diameter flue will support a fireplace opening up to about 550 x 550 mm (22" x 22") (see Building Regulations J 2.2.) For bungalows, the ratio should be reduced to 1/6th. A major advantage of precast fire chest and chimney flue systems is that the ratios have been carefully worked out and so are guaranteed to function properly.

If you are building a new chimney, take note at what works for the surrounding properties. They will already have been built or adapted for the local environment.