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Z-Flex Z-Vent Stainless Steel Venting Tips
We stock a HUGE supply of both 3" and 4" Z-Flex Z-Vent Stainless Steel Venting. And, we now carry 5" Stainless Steel Venting! Why Z-Flex products? Simply because they are the best!
Our 3" Z-Flex Z-Vent stainless steel vent pipe mates up directly with the following Bosch Vent Kits:
- Bosch AQ3ES Horizontal Vent Kit (used only with the Bosch 2700ES / 2400ES heaters)
- Bosch ES VVT Vertical Vent Kit (used only with the Bosch 2700ES / 2400ES heaters)
- Bosch AQ3 Horizontal Vent Kit (used only with the Bosch 2400E / 250SX / GWH 635ES heaters)
Bosch requires that either 3" or 4" stainless steel vent pipe (AL29-4C) be used when installing the Bosch AquaStar 2700ES / 2400ES / 2400E / 250SX / GWH 635 ES / GWH 715 ES model heaters. The GWH 345 ESR and GWH 450 ESR heaters require 3" stainless steel vent pipe (AL29-4C).
Using other types of venting with the Bosch 2700ES / 2400ES / 2400E tankless water heaters will void your warranty and put your family's health in serious danger. Many of our Bosch 2700ES / 2400ES / 2400E tankless water heater customers ask us if they can use their existing venting. The answer is always NO. And, the Bosch 2700ES / 2400ES / 2400E tankless water heaters must have their own dedicated venting system.
 Most customers use the 3" venting with the Bosch 2700ES / 2400ES / 2400E tankless water heaters. If you choose to use the 4" venting, you will need the 3" to 4" Increaser Z Flex Z Vent SS Venting (2SVSI0304).
The two main reasons to use 4" venting with the Bosch 2700ES / 2400ES / 2400E tankless water heaters is if you already have the 4" venting in place or if you intend to go literally straight up with no elbows (see comments below).
Customers installing non-Bosch tankless water heaters often require 4" stainless steel venting. Many of these customers require our 4" Universal Adaptor: Takagi, Paloma, Rheem, Noritz (2SVSNA04.5) to connect their water heater to the 4" piping system. We also carry the 3" Rheem/Paloma Adaptor (2SVPA03) for connections to certain Rheem and Paloma tankless water heaters.
Some of our customers take great care to measure exactly the distances of their pipe runs. Sometimes they have to come back to us to purchase an additional length of pipe.
Here's a tip: Buy a length of straight run pipe that is a little longer than you need. Each piece of straight run pipe can be cut with a hacksaw. You must leave at least 1.5 inches at the male end of the pipe so that it will snug up with the female gasketed end of the next piece of Z-Flex vent pipe. Any part of the male end of the pipe you cut off must be discarded as it no longer has the gasketed female end.
You do NOT need to purchase gear clamps to connect the stainless steel pipes to each other. Each female end includes a clamp and a sealed gasket to ensure a tight and snug fit. Gear clamps are only needed to secure the intake air hose to the Bosch 2400E collar and again to the intake air termination box.
We do sell the Z-Vent Sealant 3oz Tube (2SILRRTV1O6X), but sealant is NOT needed to connect one piece of Z-Vent pipe to another. The sealant is only needed to help ensure that there is a tight connection between the Top Support / Support Collar and the 3" vent pipe so that rain water does not run down the outside of the 3" vent pipe and into the flashing. Sealant is also needed in certain applications in which the normal connections cannot be made, such as when certain Z-Flex adaptors without gasketed seals are used.
For our customers who purchase the Bosch 125FX, we automatically include the FXHOOD. However, you will need a 4" x 90 degree elbow and usually some straight run pipe. We strongly suggest that all Bosch 125FX customers purchase the Bosch 125FX / 425EF Adaptor to make a perfect seal between the heater and the venting system. All of these 4" venting parts can be found on our 4" stainless steel venting page.
Bosch 2700ES / 2400ES Condensation and Rain Strategies
The Bosch 2700ES / 2400ES tankless water heaters do NOT come with built-in condensation drains.
The Bosch 2700ES / 2400ES Installation Manuals states that the Bosch 2700ES / 2400ES tankless water heaters requires the installation of an external condensate drain for:
- ALL vertically terminating vent installations;
- All Horizontal terminating vent installations where the total vent length is greater than 10 feet; or
- Vent installations where any section of the exhaust vent pipe passes through an unconditioned space
Bosch recommends to install the additional condensate drain as close to the heater as possible.
There are three 3" Z-Flex Z-Vent condensation drain parts that you can choose from:
Each of these will require a Condensate Drain Kit (2SVEDTK24).
 The 3" Vertical Condensation Drain Tee (2SVEVWCF03) acts as a 90 degree elbow and is the best choice for catching condensation and rain as it has a large reservoir.
 Not all horizontal installations have an opportunity to use the 3" Vertical Condensation Drain Tee and they should therefore use the 3" Horizontal Condensation Drain Pipe (2SVEDWCF03) to replace a straight section of pipe.
 The 3" Vertical Condensation Drainpipe (2SVEVDP03) has the least capacity for removing condensation and rain. It should be used as a last resort and only when 3" venting goes literally straight up from the heater. It is preferable to offset the Bosch 2400E from the vertical vent pipe and use the 3" Vertical Condensation Drain Tee (as a 90 degree elbow) along with an actual 90 degree elbow.
If you must go straight up from the Bosch 2700ES / 2400ES / 2400E heaters, we recommend that you use the 3" to 4" Increaser (2SVSI0304) and then run 4" Z-Flex Z-Vent venting. This will allow you to use the larger 4" Vertical Condensation Drainpipe (2SVEVDP04). This 4" drainpipe has a much higher capacity for removing condensation and rain than does the 3" drainpipe.
Bosch 2400E / 250SX Condensation and Rain Strategies
The Bosch 2400E / 250SX tankless water heaters require two condensation drain points on the exhaust system.
The Bosch 2700E / 250SX Installation Manuals details these requirements.
Bosch has also recently released a Service Bulletin on the Bosch AquaStar 2400E Condensation and Rain Prevention Requirements.
This bulletin states that Bosch Water Heating now requires the installation of an external condensate drain (in addition to the one supplied with the heater) for ALL vertically terminating vent installations and Horizontal terminating vent installations where the total vent length is greater than 5 feet.
Bosch recommends to install the additional condensate drain as close to the heater as possible.
Preventing Your Bosch 2700ES / 2400ES Heat Exchanger from Freezing
Written prominently in the Bosch 2700ES and Bosch 2400ES Installation Manual:
Warning: In areas where outside temperatures routinely come close to freezing, sealed combustion operation
is required. Use separate terminations for combustion and vent, which must be
installed on the same wall or roof surface, however never facing the direction of prevailing winds. Failure to
do so may result in heat exchanger freezing up and bursting. This failure is not covered under the manufacturer's
warranty.
Take this warning seriously!
The reason that a sealed combustion operation (twin pipe system) is required may surprise you. In freezing areas Bosch requires that you bring inlet (combustion) air in from the outside. You may think that this would put the heat exchanger in more danger of freezing. BUT, it actually helps prevent the heat exchanger from freezing!
If you live in a freezing area and you take the inlet air into your Bosch 2700ES or Bosch 2400ES tankless water heater from the inside of your home, you actually create a situation that encourages cold air from the outside to be sucked through the exhaust pipes, across your heat exchanger and out the inlet intake whenenver the tankless water heater is not running.
In particular, if you have a furnace located near your tankless water heater and if that furnace draws its combustion air from inside of your home, then it will create a negative pressure (vacuum) in your home. To get its combusition air, it may end up pulling air from the outside of your home backward through your exhaust system. As this cold air passes backward over your heat exchanger it may cause your eat exchanger to freeze.
Bosch also requires that the inlet and outlet vents be installed through the same wall or roof to ensure that a pressure difference does not exist between the inlet and outlet side which could also cause air currents through the heater.
Another point to note is that Bosch requires that you use a minimum of 3 ft of straight pipe when installing your Bosch 2400ES or Bosch 2700ES tankless heaters. The AQ3ES Horizontal Vent Kit comes with just more than 3 ft of straight pipe. Make sure that you use all 3 feet of the straight pipe to meet the installation requirements.
The good news is that if you live in a freezing area and if you follow the Bosch installation manual by installing with the twin pipe system through the same wall or roof, using at least 3 ft of Z-Flex stainless steel straight pipe for the exhaust you will avoid this problem and protect your heat exchanger!
Wall Support System
It is important to provide the proper support to vertical venting systems and long horizontal venting systems. The 3" Wall Support (2SVSWS03) and 4" Wall Support (2SVSWS04) provide this support while also ensuring that the hot venting system stays one inch away from combustible materials. Vertical supports are required after any 10 foot run. These vent supports may also be used to support long horizontal runs, which require support every 6 feet.
We now carry all of the 5" Z-Flex Stainless Steel Venting parts that are used by some tankless water heaters as well as by Commercial Boilers.
Z-Flex Z-Vent Documentation
We carry the full line of NovaFlex Z-Flex Z-Vent Stainless Steel Venting parts. Please contact us for a competitive quote on any diameter venting parts, even if we have not listed the parts on our web site. The following documentation may help you find the Z-Flex parts you are looking for:
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