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Thread: Proper Venting of Rheem Condensing tankless water heater

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    DIY Member Killer95Stang's Avatar
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    Default Proper Venting of Rheem Condensing tankless water heater

    I finally decided to bite the bullet and purchase a tankless water heater. Not to save tons of money, because how much can I really save when my gas bill ranges from $12 - $20 at its peak. What I do plan on getting is a little extra real estate, so I can install a water softener where the current 40 gallon tank is. Not to mention, I would like to take advantage of not having to time the washing of clothes when I decide to take long shower.

    So.. after a little researching here and there.. I might have decided that I want to buy a Rheem Tankless water heater. I like the added benefit of a condensing unit, since they say I can direct vent the unit with PVC pipe. But that leaves me at a couple questions.

    1. Is PVC legal to use as a vent in CA?

    2. Can I horizontally vent my units exhaust into a covered exterior patio area? I currently have a roofed patio which extend from one side of the house to the other (approx 60ft x 12ft x 9 ft tall). All sides are fully open to the back yard with the only side not open being attached to the side of the house. I'm pretty sure I know the answer to this, but I'll ask anyway.

    3. Does anyone have real world pictures of how they terminated PVC intake / exhaust vents out of the roof. I have plenty of diagrams that I've seen on various websites, but no pictures of actual in use vents.

    4. Rheem sells a vertical / horizontal PVC two into one vent stack. It appears that the exhaust portion stays open. How do you cap this off so rain doesn't go back into the exhaust piping? This is another example where I can't find any pictures of it in actual use.

    5. My current tanked water heater vents straight up through the roof. I would be putting the tankless in the same spot, so I will have no horizontal runs of pipe for a condensation drain fitting. Do I need one with a condensing unit? The directions are pretty vague.

    Here's an example of the termination kit that Rheem sells



    I plan on using either the Rheem H84 or H95 condensing units in a 2 full bath house with only my wife and myself living there.

  2. #2
    In the trades Dana's Avatar
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    PVC rated for venting is legal in CA for condensing units.

    Venting is allowed under a soffit or shed-roof or covered patio that is not walled-in, so long as you meet all clearance requirements to operable windows, doors & air-intakes. IIRC you need a minimum of 2' of vertical clearance between the vent and the overhanging roof/soffit.

    It absolutely need a means of dealing with flue condensate, particularly if you have long vertical runs. Short side-vent runs incur less condensate volume, but condensate traps/drains are still a good idea there too (especially in cooler climates) rather than letting it run and drip out the side. There MUST be some amount of slope in the lateral the drops away from the tankless and toward the condensate trap/drain- allowing flue condensate run back and drip onto the heat exchanger will damage it. A sideways-U may be needed in the venting directly above the tankless to accommodate it in your otherwise all-vertical installation. Four ells to form the U knocks something like ~6' off the maximum allowable length, but unless this is a 3 story house with the tankless in a basement you'd probably be able to roof-vent it if desired (you're allowed ~33' of straight section with 4 ells.) That many ells would also require 3" rather than 2" vent.


    Roof terminations can be either a combined concentric version as in your picture, or separate, with the intake being an inverted-U:



    In snowy areas (not SoCal) side venting is much preferred, since the localized melting from the heat of the vent contributes to ice-damming issues.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    On the concentric units, the exhaust goes out the middle, and the intake around the outside of it. This cools off the exhaust, and prewarms the intake. This technique is used on most condensing, high-efficiency burner units.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member saphman's Avatar
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    I just installed the exact tankless heater you have except mine is the Paloma PHH- 32DVN. MY vent run is all vertical with 3" PVC terminating out the roof with the concentric 3" vent you show in your thread. I have also asked the same question regarding rain ingress into the exhaust.

    I have been told by multiple experts that it is ok for rain water to enter the exhaust. It will flow out of your condensate port which is under the heater on the left rear as you face the unit. You CANNOT however allow any water to enter the combustion/intake side. For this you need a condensate trap. There is a 3" rubber condensate ring that can be purchased and is mounted on the intake stack just above the heater to trap any condensate there. It has a side port that you connect a drain line to.

    I am also told The rain cap is left off the concentric vent exhaust because it could create back pressure which will trigger an error code. The Intake side is UNDER THE CONCENTRIC RAIN CAP. The picture shown above show two pipes and it appears that the intake has the "Candy Cane" elbows to keep rain out.

    Make absolutely sure that if the unit is mounted indoors that you have a reliable way to route the condensate runoff. I suggest you follow the manual EXACTLY. This is a very complex heater and if not installed correctly you will have error codes and problems. They specify the exact type of 3" PVC. It cannot be foam core pipe. It has to be ASTM-1785

    The gas supply is also critical and needs to be a 3/4" supply MINIMUM. I did mine with 3/4 " CSST off my Gas manifold. We have a 2 PSI system. You will also need a regulator. This unit is 200,000 BTU's! A standard water heater is only 40,000.

    If you would like to email me I would be happy to help. The heater is excellent by the way and works flawlessly. If installed correctly, you will be very happy. Do it right the first time or you will be sorry. Get permits and have it inspected. Hire a pro if you have any doubts especially with Gas or plumbing.

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    DIY Member Killer95Stang's Avatar
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    Quote Originally Posted by saphman View Post
    I just installed the exact tankless heater you have except mine is the Paloma PHH- 32DVN. MY vent run is all vertical with 3" PVC terminating out the roof with the concentric 3" vent you show in your thread. I have also asked the same question regarding rain ingress into the exhaust.

    I have been told by multiple experts that it is ok for rain water to enter the exhaust. It will flow out of your condensate port which is under the heater on the left rear as you face the unit. You CANNOT however allow any water to enter the combustion/intake side. For this you need a condensate trap. There is a 3" rubber condensate ring that can be purchased and is mounted on the intake stack just above the heater to trap any condensate there. It has a side port that you connect a drain line to.

    I am also told The rain cap is left off the concentric vent exhaust because it could create back pressure which will trigger an error code. The Intake side is UNDER THE CONCENTRIC RAIN CAP. The picture shown above show two pipes and it appears that the intake has the "Candy Cane" elbows to keep rain out.

    Make absolutely sure that if the unit is mounted indoors that you have a reliable way to route the condensate runoff. I suggest you follow the manual EXACTLY. This is a very complex heater and if not installed correctly you will have error codes and problems. They specify the exact type of 3" PVC. It cannot be foam core pipe. It has to be ASTM-1785

    The gas supply is also critical and needs to be a 3/4" supply MINIMUM. I did mine with 3/4 " CSST off my Gas manifold. We have a 2 PSI system. You will also need a regulator. This unit is 200,000 BTU's! A standard water heater is only 40,000.

    If you would like to email me I would be happy to help. The heater is excellent by the way and works flawlessly. If installed correctly, you will be very happy. Do it right the first time or you will be sorry. Get permits and have it inspected. Hire a pro if you have any doubts especially with Gas or plumbing.
    Thanks for you reply... I actually haven't bought the unit yet. I wanted to know the answer to the venting issues first, plus I can't decide between the Rheem RTGH-84 or RTGH-95. I have a small 1300sq ft house, with 2 baths and only two occupants at the moment (my wife and myself), so on paper the RTGH-84 is all we need with headroom to spare.

    Hearing a definitive answer on that concentric vent is music to my ears. That will save me from have to add an extra hole in the roof.

    Do you have any part numbers for that rubber condensate trap? As far as the condensate run off goes, I have a washing machine drain in close proximity that I can probably tie into.

    I'll make sure to purchase the correct PVC piping for the exhaust vent. With the location of the water heater and pitch of my roof, I'll probably only need about 3 ft of 3" pipe to complete the job.

    I have already contacted the gas company and they stated that my meter and whole house gas requirements will allow me to add the 199,000 BTU burner unit without issues. I just have to re-plumb part of the gas system, to give me a 3/4" line to the water heater. Currently the meter enters the house with 1" pipe and then branches off in the attic to pickup the Central Heating, Stove and current water heater.

    I would love to see a picture of your installation if possible.

    Thanks again..

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    DIY Junior Member saphman's Avatar
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    I bought my tankless unit from Low Energy Systems out of Denver. They are a very good company and provide excellent tech support. They have the rubber 3" condensate coupler you will need for the air intake side. Also make sure you get the tankless service valves so you can do the required maintenance.

    You can run your condensate line from the heater to a sink. I simply fitted my laundry sink with a 5/8" dishwasher tee and plumbed in above the drain p trap. Works perfectly.

    If you decide to use a roof penetration you will need a storm collar for your concentric vent. I bought a 4" stainless flashing umbrella from SBC flashings out of Miami. This clamps around the 4 1/2" od cencntric vent pipe and seals your roof jack from rain entry.
    I will try to send you some pictures of the installation.

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    DIY Member Killer95Stang's Avatar
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    Quote Originally Posted by saphman View Post
    I bought my tankless unit from Low Energy Systems out of Denver. They are a very good company and provide excellent tech support. They have the rubber 3" condensate coupler you will need for the air intake side. Also make sure you get the tankless service valves so you can do the required maintenance.

    You can run your condensate line from the heater to a sink. I simply fitted my laundry sink with a 5/8" dishwasher tee and plumbed in above the drain p trap. Works perfectly.

    If you decide to use a roof penetration you will need a storm collar for your concentric vent. I bought a 4" stainless flashing umbrella from SBC flashings out of Miami. This clamps around the 4 1/2" od cencntric vent pipe and seals your roof jack from rain entry.
    I will try to send you some pictures of the installation.
    I would appreciate some pictures.. I still can't find any other references to that rubber condensate trap you bought. I'll call LES later on today and ask about it.

    Thanks

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    DIY Junior Member saphman's Avatar
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    Default Installation Pictures

    Here are a few pictures of my tankless heater in the utility closet. You can see the two 3" PVC conduits and the rubber condensate collector on the air intake.
    I also added a 3" 'T' above that just in case.

    By the way if you do use a concentric vent, Do not cement the rain cap to the pipe. If you do that, you wont be able to service the vent if you need to such as repairing or changing the roof flashing, or if something gets into the vent itself.

    Also, remember that this unit is basically a computerized water heater. Like any sensitive, expensive piece of electronics, it should be protected by a good surge protector. I used a ups for a computer. I will also be adding a Siliphos Aquapure filter in the cold water line to help prevent scale and sediment.
    Attached Images Attached Images    

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    DIY Member Killer95Stang's Avatar
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    Thanks for the info and pictures... I called up LES and ordered the coupler and a set of the service valves. Now I just need to decide on which unit to buy... I technically will have more than enough hot water with the RTGH-84, but the H95 model is the same exact price. Can I go too big with a tankless? Will I waste more gas supplying the same amount of hot water? I might just call Rheem tomorrow and ask for their opinion..

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    Retired Defense Industry Engineer jadnashua's Avatar
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    On most, the burner modulates so that the water going through gets to the proper temp..bigger unit, higher max output.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member saphman's Avatar
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    Rheem, Richmond, Paloma and Wai Wela are the same units internally. I have had several contacts with Rheem Tech Support and they are terrible. I am sorry to say that but it is true. The people they have on staff know very little about the products they sell. IMHO, you are better off talking to the guys at LES. They are installers as well with excellent experience with these units.

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    DIY Member Killer95Stang's Avatar
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    I ended up purchasing the the Rheem RTGH-95DVN from an online plumbing supply with a brick & mortar location that is local to me. I also bought the PCV concentric intake/exhaust vent tube from the same location.

    Saphman.. Did you purchase the storm collar directly from SBC, or are they sold at a local plumbing supply shop? Does it have to be clamping style?

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    DIY Junior Member saphman's Avatar
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    Yes. I ordered it directly from SBC. You will need the Stainless steel flashing umbrella. It comes with an adjustable ring clamp to tightly secure over the outside of the Concentric vent with a bead of caulk. Cost was about $38. The collar size you need is 4.5 inches.

    If you are using an existing penetration on your roof, you will need to upsize the flashing to accomodate the 4.5 inch vent. My roof had a standard 3.5 inch class B water heater pipe and flashing. We simply cut the existing flashing a little to allow the 4.5 inch od pvc pipe to go up thru. We caulked that and then slid the storm collar down over that. It was easier than tearing up our roof and replacing shingles.

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    In the trades Dana's Avatar
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    Quote Originally Posted by Killer95Stang View Post

    <snip>

    I have already contacted the gas company and they stated that my meter and whole house gas requirements will allow me to add the 199,000 BTU burner unit without issues. I just have to re-plumb part of the gas system, to give me a 3/4" line to the water heater. Currently the meter enters the house with 1" pipe and then branches off in the attic to pickup the Central Heating, Stove and current water heater.

    I would love to see a picture of your installation if possible.

    Thanks again..
    Think again about using 3/4" goods- with a 199K burner a 3/4" line would only get you 10' from the meter, with no ells or tees.



    ^ (the numbers in the grid are max-kbtus) ^

    Almost every real-world installation needs 1-1/4" gas lines up to the unit, with a reducer for making the connection. Undersizing the gas lines introduces a whole load of operational misery, especially when the furnace fires up. Do it right the first time and save yourself the pain of having to rip it out and start over. Very-short sections of 1" or 3/4" aren't much of a problem, but I do mean VERY short, with as few turns in the skinnier pipe as possible.

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    DIY Junior Member saphman's Avatar
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    Dana, what is the reference inlet pressure for the gas table you listed?. Is that 1/2 PSI? The reason I ask is I used 3/4" CSST running 75 feet from my gas manifold. According to the table I used that was plenty of reserve CFH. My system is 2 PSI. I also have inline a 3/4" Maxitrol regulator.

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