What the direct vent water heater is, how it works, review of the main features, buying and installation tips. Review of the most popular manufacturers: Rheem, AO Smith and Bradford White.
Either buying a direct vent water heater for the new or old house, the proper location and venting should be considered, no matter what type of the fuel will be used; natural gas, liquid propane or oil. If buying an electric type you don't have to worry about venting or combustion gases and you will not have additional expenses either.
Direct venting requires plenty of fresh air for the heater's proper combustion and ignition. The combustion air can come either from the outside through the venting pipes, or from the inside of your home. With the direct venting (DV), the fresh air for gas combustion comes from the outside through the outer vent, while the products of combustion are safely removed directly to the atmosphere.
For the correct venting, venting pipes have to be installed per local codes and manufacturer's instructions.
Direct venting water heaters utilize mainly concentric or coaxial venting system (pipe inside the pipe), where the inner pipe is for the air intake while the outer pipe for the exhaust.
Buy the direct vent water heater if there is no chimney in your house or one close to the heater, and if there is no electrical source. Since it does not require electricity, you will have the hot water even during the power outages. If the electricity is not an issue you can still go with the advanced direct models, that use the electric blower for the exhaust, and these are called power-direct vent models. Direct venting is also better than the power venting as there will be no pilot outages due to the air pressure changes.
Direct vent gas water heaters are designed with a sealed combustion chamber that is air tight so back-drafting will not occur. They are silent, as there is no fan to blow, and safe, so the installation won't be a problem. There is no risk of the Carbon Monoxide leaking so they can be installed virtually anywhere as they draw the fresh air in from outside.
Some types of DV heaters can be installed close to an outside wall, while others further away, it depends on the recommended pipe length.
Direct venting is found in both tank-type and tankless units.
Direct vent water heater is safe because it has the sealed combustion chamber that prevents the fumes from going back into the house. The unit always works with the outside fresh air so no air from the inside of the house is used.
Direct vent water heater can use the PVC, CPVC or ABS pipes that allow an easy and economical installation. Direct venting can be installed either horizontally or vertically, which depends on the installation options, both allowing efficient work and great flexibility for the users.
Direct venting works with the vertical pipes as the heated warm/hot exhaust fumes are lighter than cool air so it is moved up and out naturally. In a case of horizontal pipes, the sealed combustion chamber is what helps in the extraction of the products of combustion and air intake. Venting should be as direct as possible with a minimum number of turns and pipe fittings. It allows installation in smaller spaces.
The vent system must terminate with the proper clearances and per local codes in order to prevent blockage, condensate or vapor to create a nuisance or hazard, property damage, or damage to the component parts and affect proper water heater operation.
Note: During installation all vent-air intake joints should be sealed (sealant is usually provided).
Almost every manufacturer in the US and Canada makes the gas water heaters with the direct venting. Most of the units are not Energy Star compliant due to the low energy factor.
Rheem, the manufacturer of popular water heaters produces several types of direct vent heaters:
Professional Classic series comes with the horizontal venting option only and is built in two sizes; 40 and 50 gallons. The adjustable coaxial vent provides flexibility in installation that can swivel 360 degrees. The horizontal and vertical kits are available for longer venting, up to 48" max.
Professional Classic series for Manufactured housing (not available in Canada, only in US). Warrior DV is the direct vent and Warrior DVX is the vertical co-axial unit. Three models are available; 30, 40 and 50 gallons.
Performance series - built in 30 and 40-gal capacities and designed for manufactured housing, for sale in US only.
AO Smith water heaters with the direct venting are found in greater number than Rheem, and also with more size variety; from 30 to 75 gallons:
ProMax Ultra Low NOx Direct Vent offer horizontal venting, through the outside wall, and vertical venting through the roof. The maximum lengths are 27" for horizontal and 100" for vertical installations.
Energy Saver for manufactured housing comes with the 30, 40 and 50 gallon tank sizes, both utilizing natural gas and propane. Thanks to the Green Choice gas burner, the NOx emission is greatly reduced. Maximum vertical height of the exhaust pipe is 96" while the intake air vent is packaged at the bottom.
Defender Safety System DS models utilize a coaxial vent pipe that is used in homes and rooms where the sufficient air for gas combustion cannot be provided. The pipe can rotate for more flexibility. Telescoping vent kits allow up to 8 feet in lengths while the flexible vent kits up to 100".
Defender Safety System High Input DH models, as the above models, do not require electricity; they utilize co-axial direct vent system with the same length capability, but offer greater recovery, have bigger tanks (up to 75 gallons) and provide side connections for space heating.
Manufactured Home Direct vent water heater
Power vent water heater is similar to direct vent option, but it uses an electrically powered vent for assistance. You can use the fan-assisted venting system if there is no chimney as an option, if there are too many turns, and if you have an access to the electrical power.
Direct vent water heater will not affect or be affected by other appliances or changes in pressure inside the home, while powered vent heater can. When installed in the building, PV, can contribute significantly to building depressurization and affect the performance of other combustion appliances.
Indoor tankless gas water heaters can also be vented directly, either vertically or horizontally to the outside, by using the manufacturer's approved venting kit.