The use of vents for coal- and wood-fired appliances is critical for ensuring proper operation and safety. L type vents, which are typically intended for gas appliances, are not suitable for solid fuel appliances such as those that burn coal or wood. This is largely because L type vents do not have the necessary construction and capabilities to handle the higher temperatures and potentially corrosive byproducts generated by solid fuels.
On the other hand, V type and S type vents are specifically designed for use with solid fuel appliances. They are built to withstand the associated high heat and byproducts without structural failure, making them more appropriate for coal and wood-burning equipment. Similarly, D type vents are categorized for double-wall construction that also accommodates solid fuels safely.
In conclusion, L type vents are not appropriate for coal- and wood-fired appliances due to their construction limitations and inability to handle the specific demands of solid fuel combustion.