6. Lack of combustion air:
This is a major topic, and we won’t be able to cover everything here. Combustion air does a few things: It provides oxygen for the fire, ventilates the appliance, it feeds an open draft hood to maintain draft, and it replaces the air leaving the building with fresh outside air in order to maintain neutral pressure. In older homes, before the codes were loaded down with provisions for energy conservation, homes were leaky and interior air calculations were either done or not done to provide sufficient combustion air. A naturally leaky home will naturally allow replacement air (combustion air) to enter—this is one method allowed in the code. When the home was built, and the water heater installed, and combustion air designed, the water heater was likely in an open unfinished basement. This offered a large volume of interior combustion air. With the air sealing of homes and the finishing of basements— which often includes enclosing mechanical equipment in some sort of closet—interior combustion air gets choked off, and naturally drafting appliances get starved of air.
7. Insufficient vent and vent connector slope:
Though this is rarely feasible, the ideal vent or chimney system is entirely vertical. More often, fuel fired water heaters connect to a vent or chimney by way of a vent connector, which is just another piece of pipe. The connector should be as short as possible and must slope upward from the water heater at a slope no lower than ¼ inch to 12. Once it connects to the vent, things get more complicated. The general idea is that the vent runs vertically, with offsets no greater than 45 degrees from vertical, but that is not the whole story. Vent slope limitations hinge on a number of variables, including the type of vent, diameter of the vent, length of the vent, among other things. Once a house is built and the vent system designed, it is no easy task to evaluate and modify it later. When finishing basements, owners often find the water heater isn’t where they’d like it, so they move it and connect it back to the original vent with a long, low slope vent connector. Long horizontal vent runs can greatly reduce the drafting ability of natural draft appliances and could lead to backdrafting of combustion gases into the home, creating a major safety hazard.
8. No support for plastic vents:
High-efficiency power vented water heaters with plastic, sealed vents are popular, especially in newer homes, and as replacements for older conventional water heaters. They eliminate the issues with conventional vent clearances and slope, and can also relieve the issues of interior combustion air. The plastic vents can be installed horizontally, but they must be supported according to the manufacturer’s specifications. Water vapor produced during combustion will condense inside these vents, so they must be sloped to drain. Often these horizontal vent pipes are fished over finished ceilings in a basement and left unsupported. A sag in the vent can potentially allow water to accumulate and affect the safe and efficient operation of the appliance. Although not ideal for anybody, sometimes a finished ceiling needs to be cut to install proper support for the vent.
9. Sediment traps that don’t work:
A drip leg and a sediment trap are usually considered the same, but not by the code. A drip is only required when wet gas (gas with a small amount of liquid present) exists. A drip just needs to allow gravity to collect the liquid in the low spots. A sediment trap is required when an integral trap is not provided in the appliance – and it usually isn’t. From manufacturing to service, gas pipe goes through quite a bit of handling, cutting, and threading that can leave some debris in the pipe. This debris can be small enough to get caught in the flow of the gas. Unlike a drip leg, gravity alone will not separate the sediment from the gas stream. A sediment trap requires a hard turn that the gas can flow around but sediment can’t. Installing this correctly has been so misunderstood in the industry that the 2012 edition of the International Fuel Gas Code added a figure drawing to show how it should be done.
10. Incorrect draft hood connection:
Water heaters are tested and provided with their specific draft hood, but it doesn’t come attached, it’s in the box separately. A professional water heater installer must attach the hood that came with the new appliance, and this almost always requires fasteners. When an inexperienced homeowner tries to do this, the hood from the old water heater is often used on the new one. Even more often, the new hood is used but not properly fastened, the screws provided are still in a bag with the instructions and glued to the side of the water heater. This is a very embarrassing way to fail inspection, so don’t ever forget the important screws.