Installing a tankless water heater in your household is a smart decision. Not only will you be reducing your energy costs by up to 50%, but by choosing a gas or propane-powered unit, you will also be minimizing greenhouse emissions by approximately 61%. As opposed to standard tankless electric heaters, gas-powered units need proper venting. Misconceptions about the venting process involved in gas-powered water heaters in most cases make construction professionals refrain from recommending these units. We explain everything you need to know about venting to enable you to make an informed decision.
Why do gas-powered units need a venting system?
These units heat the water through the combustion of gas. In the process, heat, moisture, and exhaust gases, including carbon monoxide, are produced. The purpose of the ventilation is to rid the home of these byproducts. This makes is a critical safety feature. Ensuring that you vent your tankless water heater as per the manufacturer’s recommendations is vital for its optimum functionality.
Different ways of venting your tankless water heater
Gas-powered tankless water heating units could be vented in two ways: direct-vent or power-vent. The difference between the two is that the former makes use of an exhaust pipe or a chimney to get rid of the exhaust gases, while the latter uses an electric venting fan to perform the same function.
Acquiring a direct-vent unit results in lower energy costs as the exhaust gases are emitted without the use of electricity. As a direct-vent tankless water heater has to pull in air from the outside, it has two columns. The use of outdoor air makes this unit ideal for small places such as a closet, attic or a mechanical room. On the other hand, a power-vent unit will result in additional energy costs. While they require only a single exhaust vent, they must be placed in a more spacious area or a place with other vents so that they acquire sufficient make-up air for the combustion of the gas.
One drawback of the power-vent units is that they produce some noise when the fans are blowing the exhaust fumes out of the home. While the noise is not really distracting, it is something that anyone looking forward to acquiring this vent type should be aware of. However, the noise could be entirely eliminated or reduced if the venting is installed correctly.
The venting could either be through the roof or through horizontal venting to the side of the house. Most homeowners strive to keep the venting run short, thus minimizing the costs. One way through which such establishments dramatically cut down on venting costs is by installing outdoor tankless water heaters such as Rinnai V75EN 7.5 GPM Outdoor Water Heater.
Indoors vs outdoors tankless water heater
Outdoor tankless water heaters require no venting, a quality that could prove problematic if they are installed in locations whose temperatures drop lower than the freezing point. While most manufacturers offer freeze protection, any exposed pipes still pose a problem in extreme weather conditions. While some units will require you to drain the unit before the cold season, others have an electric heater that keeps the unit from freezing. Therefore, outdoor tankless water heaters will prove more useful in places with warmer climates.
While indoor units will take up some of the living space, outdoor units occupy none. You can have them installed anywhere as long as they can be connected to the plumbing and electric system. As they are outdoors, they need no venting.
Your preference will be highly influenced by your home’s structure. For existing homes, an outdoor unit may come in handy as there will be minimal adjustments to its plumbing or venting. An indoor unit could be a better option if you are in the process of constructing a home. The home will be designed with the unit in mind and incorporate all the plumbing and venting aspects.
How to install an indoor unit for easier venting
Most times it makes more sense to have the tankless water heater installed near the outside wall and adjust the home’s plumbing rather than install longer vents. You could also have the unit installed in the basement. This only requires a few feet of vertical venting which can then be redirected to the side of the house with a 90º elbow such as Rinnai 224063 Vent Pipe Elbow. Placing the unit near the outside wall could also free up some much-needed space.
When you choose the horizontal venting, you should slope it in a way that prevents the flowing back of the condensate into the unit. Alternatively, create a condensate drain at least 3” from the vent connection. Should the condensate flow back into the unit it will destroy the heat exchanger hence shortening the unit’s lifespan. In recent times, we have seen manufacturers provide drain tees for vertically installed venting to protect the tankless water heaters. Homeowners have the option of buying store bought drains such as Z-Flex Z-Vent 4” Vertical Condensation Drain Tee.
The most suitable vent piping material is Category III, which is normally AL29-4C Stainless Steel, although sometimes it could be other materials such as copper or PEX. This material averts the formation of condensate within the venting system and the unit itself. Although in very small quantities, the condensate is highly acidic and it destroys standard vent materials within no time. In addition, the piping material used in venting needs to be sealed so as to prevent the leakage carbon monoxide due to the positive pressure created by the fan within the unit.
In the case of large residences or commercial applications where multiple units will be installed, you do not have to install multiple ventilation. Most manufacturers have come up with a common venting system which can be shared by up to 10 units.
Can my tankless water heater share the same venting with the furnace?
Tankless water heaters fall into the Category III appliances which are machines that operate with positive vent pressure. Most furnaces, on the other hand, are Category II. This makes it not suitable to use a common vent as it would pose a potential fire hazard. In addition, the unit’s venting should not be connected to the home’s masonry chimney without lining it with a suitable vent pipe.
However, homes installed with standard efficiency furnaces, that is 80%, could have the venting combined with that of the tankless water heater. Always follow the manufacturer’s recommendations and familiarize yourself with the local building codes.
Incorrect ventilation could have dire consequences which include:-
- The unit’s failure as the condensate finds its way back into the unit.
- Carbon monoxide poisoning due to backdrafting. This refers to a condition where the exhaust from the unit fails to leave the home through the vent and instead stays in the house. Backdrafting is mostly caused by poor vent installation or design and in some cases, an imbalance of the air volume within the home. Imbalance in the air volume is mostly due to kitchen or bathroom vent fans which pull the air out of the home. This creates a vacuum effect, thus drawing the exhaust from the unit into the home.
Venting of a tankless water heater does not have to be something that you loathe. With proper planning, it is quick, less invasive, and affordable.