Tankless water heaters have been sweeping the nation with a huge growth over the last 5 years or so. These compact units mount on a wall either inside or even outside the house and supply hot water on demand literally without end! Many people believe that within the next 5 to 10 years 50% or more of all homes will have a tankless water heater in them. Tankless water heaters are available in electric natural gas and propane fired models.
Choosing the correct Ventilation is very important to gas fired tankless water
heaters. If these products are not vented
properly, many bad things can happen. The least of these is the unit may
soon in its life span due to condensate being
allowed to enter the product. At the very worse, Carbon Monoxide Poisoning
could occur. “Shortcuts” should never
be taken in regards to the venting system on this or any other
piece of equipment that burns gas, oil, wood or
other products. All manufacturers’ instructions should be followed and
you should always make sure that your heater is
Tankless water heaters can have their venting go either out a side wall with horizontal venting or up through the roof. Keeping the venting run as short as possible is both good for the heater and will help keep costs down. In fact, many times it makes sense to move the location of the heater closer to an outside wall and run the water lines to it rather than run longer venting. (Copper, PEX and CPVC are relatively cheap compared to Stainless Steel vent piping!) This also may give you a reason to get some needed space back within the home.
Most tankless water heaters require a special vent piping material. This material is known as “Category III” and is typically AL29-4C Stainless steel but sometimes may be other materials. This is required because the combustion efficiency of the heaters make it very likely that condensate will be formed within the venting system. This condensate, although there is not a lot of it, is highly acidic and will destroy standard vent material in a short time. Type “B” gas vent can not be used on most of these heaters for this reason. Another reason this vent is required is that the vent systems are under pressure from the fan within the heater. This is known as “Positive Pressure” venting and requires that the vent system be UL listed as positive pressure and sealed to prevent carbon monoxide from leaking out into the occupied space. Tankless water heaters as well as other products also have maximum lengths that you can run the venting. The number of elbows required in the system shortens these distances. Always consult your manufacturer instructions and never exceed these distances!
It is also not allowed to tie these vents together or tie them into an existing masonry chimney. The condensing gasses would quickly begin to cause damage to the masonry and result in structural damage to the property as well as a very unsafe condition with carbon monoxide. If you can run the proper vent product up through an existing chimney to the outlet and provide the proper condensate drain to protect the unit, you can use the existing chimney as a “chase” to run your new vent pipe in. (Consult individual manufacturer’s instructions!)
You should either slope horizontal venting away from the heater, or provide some type of condensate drain within 3’ of the vent connection to protect the unit from damage caused by condensate. The condensate in the venting will destroy the heat exchanger if allowed to run back to the unit. Units not vented properly will have their heat exchangers ruined within a few short years. Most vent manufacturer’s now have the ability to provide a drain tee even when venting is installed straight up to properly protect the unit.
Venting is probably the most important part of a tankless heater installation. To recap this part: No “B” vent! No Common Venting! No connecting to masonry chimney’s without lining it with the proper vent pipe. Use Stainless steel UL listed positive pressure venting made for these products. Allow for proper removal of condensate within the vent system. Keep venting runs to a minimum length. Never exceed manufacturer’s venting lengths. Read and obey your owner’s manual!