Minimum Chimney Heights
Chimney Height
Factory-built fireplace manufacturers specify minimum and maximum chimney height. Woodstove manufacturers may have similar requirements. Both types of appliances and most codes require the 10 foot/2 foot/3 foot rule for minimum chimney height above the roof:
The chimney must extend at least 2 feet above any portion of any structure within 10 feet (measured horizontally) AND must extend at least 3 feet above the highest point of its roof penetration.
The height of the chimney must meet or exceed both of the minimum requirements. If manufacturer requirements exceed code minimum height requirements, they should be followed.
These minimum heights may have to be exceeded, however, for adequate draft and satisfactory appliance performance. Additional height can help improve draft and may make the difference in marginal situations. It will not, however, cure severe draft problems. There are two situations that call for specific attention to chimney height:
- Heated portion of the house above the top of the chimney: As noted earlier, the house can act like a chimney and compete for the air supply. This action, called house stack effect, can result in weakened draft or even smoke spillage into the house.
- High altitude: Appliances may need stronger draft to deliver a greater volume of air at higher altitudes to make up for the lower concentration of oxygen. Recommended sear level chimney height may need to be increased by 2-3% per 1000 feet of elevation. Check with the fireplace manufacturer.
In general, a minimum venting system height (chimney or for some woodstoves, chimney + connector) of 15 feet is recommended. It should be noted carefully, however, that too tall a system can cause overdrafting problems. Excessive draft can cause the flue to burn to rapidly. In woodstoves, the effect of overdrafting can cause damage to the catalytic combustor and/or internal stove components that result in poor performance and/or much shorter appliance life.
|
