Sealed combustion (powered direct-vent) water heater

Discussion in 'Water Heater Forum, Tanks' started by MrStop, Nov 4, 2014.

  1. MrStop

    MrStop Member

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    I need to replace a water heater that is located in my basement. It is currently an atmospheric vented tank unit. We are preparing a remodel of our home which will include improvements to the home envelope (sealing and insulation). Therefore, I want to go with a sealed combustion heater so I don't have to pull in makeup air elsewhere. Additionally, I would like to eliminate the flue chase (HVAC is already high efficiency).

    Any thoughts on condensing vs non-condensing? Any opinions on the following makes/models?

    Rheem RHE50 - High efficiency condensing

    AO Smith Vertex GDHE-50

    HT Products Phoenix Light Duty
     
  2. MrStop

    MrStop Member

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    I have been reviewing the Rheem installation documents for their power vented units and I'm concerned that the guidelines limit the installation options considerably. The instructions (example) state:

    "Elbows are limited to a total equivalent length of 20 ft. (6 m). Maximum allowed four (4) 90° elbows or eight (8) 45° elbows" [p. 13]

    "A 90° elbow is equivalent to 5 ft. of straight pipe. A 45° elbow is equivalent to 2.5 ft. of straight pipe. The use of a 45° elbow is preferred over a 90° elbow. The vent and combustion air-inlet terminations are not included in the equivalency calculations." [p. 13]

    "IMPORTANT: Remember to include the additional 90° elbows and vertical height of the vent and combustion air-inlet pipes of the vent riser when calculating the maximum equivalent vent and combustion air-inlet system lengths. The maximum equivalent vent and combustion air-inlet
    system lengths must be as specified on page 13." [p. 17]​

    I'm a little confused on the limitations placed on the total allowable elbows. 4 elbows max seem to be limiting in the installation. It seems like you more or less have to have a straight shot out the wall and running parallel to the joists to make this work.

    In reviewing the literature on similar units from other manufacturer's they don't have the same limitations. Does the limitation only apply when using 2" PVC where you would quickly get to the max equivalent length with more than 4 elbows? Or does this apply to 3" as well, despite the equivalent lengths potentially being well under the max length?

    Additionally, there appears to be some inconsistencies in whether the air inlet pipes are factored into the total system length. P.13 indicates they are not, while P. 17 indicates they are.

    Should I ignore the guidelines for the max number of elbows and just rely on the calculated equivalent length? Should this include terminations or not?
     
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The instructions become part of the certification process, and failing to install the product within the stated guidelines (should) cause the inspection to fail, and is likely to cause less than ideal operation. So, if it says a max of 4 90-degree elbows, that's what it means. Note, that that does not include the initial take off from the unit or the termination, per the part you included above.

    IF it allows 3", then the restrictions may be less. Keep in mind that the area in a 3" pipe is 2.25x greater than that in a 2" pipe (radius^2 - 1 verses 1.5^2=2.25).

    It also makes it much harder to manage condensation with the more changes of direction. Most of these things, and certainly those that condense, need slope like a drain, to manage the condensation, otherwise, it could end up pooling and blocking off the pipe. Those that are higher efficiency but don't condense, often require SS pipe, which can get expensive very quickly, and typically slope towards the outlet, verses the unit. You have to read and understand the instructions (and follow them!) if you want a successful installation that will also pass inspection.
     
  5. hj

    hj Master Plumber

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    I would think that if you need more than FOUR elbows, you should reconsider how you are going to run the vent.
     
  6. MrStop

    MrStop Member

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    I have been giving this a lot of thought. My vent run inside the basement would look similar to the image on the left below. However, I may need to add 2-3 elbows depending on if I relocate the heater or not. So I would have 5-6 total elbows before I exit the basement. On the exterior side I would have another 3 for the terminal assembly to give me ground/snow clearance. The total elbows would need to be 8-9 for each run (+40-45 feet).

    In looking at the layouts Rheem provides, they are showing as many as 6 elbows. However, according to @jadnashua not all of these count. Is that correct?

    [​IMG] [​IMG]
     
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The documentation you provided says "The vent and combustion air-inlet terminations are not included in the equivalency calculations." IOW, those at the end of the run at the outside of the house do not count, but everything else does. To ensure you get the proper air flow and proper air mixture (required for proper combustion efficiency and CO production), you must have your system setup as originally designed. If you can't, you find a different unit, or move where it is installed, or change the run layouts.
     
  8. MrStop

    MrStop Member

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    Thanks. I must have been misreading as the two statements seemed to be contradicting one another. The latter statement must be referring to the vent riser coming off the water heater. Whereas the first statement must be just the termination I guess. So in the images I posted above I would count 3 elbows for the run, correct?
     
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Based on the printed instructions you provided, yes...that example shows three countable elbows. That would count as 15', then, plus the actual lengths of the pipe must all be less than or equal to the maximum allowed.
     
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  10. MrStop

    MrStop Member

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    Thanks for the clarification on the number of elbows. Now back to types & makes of water heaters. Any recommendations for a sealed combustion unit?

    I took some measurements. From what I can tell, my max first hour use is about 118 gallons. However, this is fairly unrealistic as it would require every family member (4) taking a shower, the dishwasher running, the washing machine running, and some miscellaneous hot water use (shaving, hand dish washing, etc). My guess is that we have a realistic max first hour use of about 78-90 gallons. Our current water heater is rated for 65 FHR. Only my wife has complained about running out of water. Additionally I have the temp set low (~120*). I understand that this isn't the healthy way to go so I'll be installing a mixing valve and running the new heater at 140*+ and then turning the temp down afterwards.

    We aren't a very water heavy household as we have low-flow shower heads and a newer HE washing machine and dishwasher. We use about 190 gallons of water per day on average. I would guess, based on my max use calcs that 100-120 gallons of the use is hot water. Also, from what I can tell our gas use for water heating is about 0.35 CCF per day with equates to 131 therms per year. Using the EPA's sticker cost of $1.04 per therm (mine averages lower), than it costs me about $136 per year to heat water.

    I have identified the following sealed combustion options. Any thoughts on brand & style in terms of real life experience?

    Standard Powered Direct-Vent Water heaters
    Condensing Powered Direct-Vent Water heaters
     
    Last edited: Nov 9, 2014
  11. MrStop

    MrStop Member

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    I ended up selecting the HTP Phoenix Light Duty PH76-50. Feature and spec-wise, the Phoenix seemed to beat the comparable Rheem and AO Smith. Also, I am hoping that the stainless tank extends the life well beyond the other two units providing less total expense over the life of the unit. I considered going tankless for a moment, but I think a tanked unit made more sense for me.

    Anyway, Carr Supply dropped off the unit today so I thought I would share some pics:

    Stout packaging protecting the unit...
    [​IMG]

    Uncrated..
    [​IMG]

    Easily accessible mechanicals; behind sits a stainless steel tank wrapped in 2" of foam...
    [​IMG]

    Connections include an auxiliary port if you want to add a hot water recirculation system or heat exchanger; includes a termination fitting for the intake...
    [​IMG]


    Next to it's soon to be 40 gallon leaky predecessor; bye-bye flue...
    [​IMG]
     
    Last edited: Nov 24, 2014
  12. Master Plumber Mark

    Master Plumber Mark Sensitivity trainer and plumber of mens souls

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    Never heard of the Phoenix..... you might have been better off with the Rheem
    because there are people who can service the unit...


    only time will tell
     
  13. MrStop

    MrStop Member

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    I'm definitely taking a leap on this one...

    I dismissed the AO smith model due to a high number of reported problems. I really didn't want to spend this type of money for something that is going to die in 3-6 years. It was a struggle between the Rheem and the HTP units. Both are relatively new, so there isn't much of a track record on either.

    I hadn't heard of HTP prior to my search either. It appears that their background has been in the boiler and commercial water heating space. A couple of persons who appear to deal more in the hydronic heating space recommended the HTP unit as their experience with their products had been favorable. What really drew me to the HTP Phoenix was its stainless steel tank, efficiency and recovery over the Rheem. While neither the HTP nor the Rheem is going to "payout" over a standard 9 year water heater, I felt the HTP would have a better payout given the extra life expectancy that the stainless tank should provide.

    In terms of service, I'm hoping this isn't an issue. However, I'm impressed at the serviceability of the unit. Every component is located right out front so you don't have to reach into the recesses of a dark tank on your side or back. I'm not as concerned about finding someone to fix the unit. I have troubleshooted and fixed just about every appliance in my home at some point or another. I have also performed car repairs of all types including a complete diagnosis and rebuild of an A/C unit (still working after 3+ years). They have a great video reference library for installation and troubleshooting (http://www.htproducts.com/forum/viewforum.php?f=117).

    Here's a video that gives a bit more detail on the HTP Phoenix:



    Like you said "only time will tell." Feel free to check back from time to time to see how this guinea pig is doing. Since you're in Indy, if you ever find your way over to Cincinnati you're welcome to come check it out in person.
     
    Last edited by a moderator: Feb 23, 2016
  14. Dana

    Dana In the trades

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    Variations of HTP Phoenix has been around at least a decade, and competes directly against the Polaris for combi hydronic heat/domestic hot water applications, but has a modulating burner (unlike the The Phoenix Light Duty is much more recent. The primary distinction with its namesake cousins is burner size (76,000 BTU/hr) and turn down ratio (3:1). For a heavy water use commercial application a mere 76K of burner is not enough, but for residential it's plenty (even if configured as a combi, in many homes.)

    One reason for going with 76K instead of 75K or smaller burner is that there are more hoops to jump through such as EF testing, whereas with burners larger than 75K it's acceptable to market water heater efficiency based on the steady-state efficiency rather than an EF test. (The Vertex has a 76K burner for similar reasons.)

    HTP is a fairly small (and IIRC, privately held) company compared to the international hot water/heating appliance players, founded about 40 years ago in Massachusetts. Most of the manufacturing is local, in an unassuming 2-3 building complex wedged between a wrecking yard and a solar farm in bucolic Freetown MA, a few short miles outside of New Bedford. Like most manufactured goods of any complexity, some sub components are purchased or contracted out for manufacture elsewhere. They were one of the first US-based modulating-condensing boiler companies on the scene, and are still in that business.
     
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  15. hj

    hj Master Plumber

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    If you have the space, using two 45s rather than two 90s for the first two turns would be a better installation.
     
  16. MrStop

    MrStop Member

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    Is using two 45*'s in quick succession better than a 90* sweep? I'm having trouble finding a 2" sch 40 90 degree sweep (DWV are more common).
     
  17. MrStop

    MrStop Member

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    I posted in another thread, but I thought I would also share my early impressions of the HTP Phoenix LD here as well:

    I have the water heater set to 140 degrees. After which, a mixing valve tempers the water down to 120 degrees. I am amazed at how fast this heater brings water up to temperature. You can monitor the water temp on the display which is pretty fun (for a geek like me). The incoming water was about 44 degree's and it was up to temp in no time.
    I gave it the torture test tonight. Four consecutive showers with one partially overlapping and hot water was to be had by all! As my family was showering, I occasionally monitored the water heater temps. I noticed that in the bathroom with a low flow head (1.85 GPM - Delta Faucet 75152 Water Amplifying Adjustable Showerhead with H2OKINETIC Technology), the water heater kept up with and slightly surpassed the hot water demand. The other shower has some older off-brand hand held that is probably 3+ GPM. In that bathroom, the water heater couldn't quite keep up and you could see temperature slipping. Near the end of the 3rd shower (which had a slight overlap with the second), the water heater temp was down to about 95 degrees. I took the fourth shower and the water was plenty hot. I went downstairs about 3-5 minutes afterwards and the water heater was already back to about 140 degrees.

    My only negative at this point is that there is a loud fan which looks like it cools an electric board. I still have part of the case off, so I hope that sound diminishes afterwards. It's in a utility room in my basement, so it shouldn't be too much of an issue. Other than that, the unit is totally quiet. I could not hear the burner nor the power vent. The only indication that it was working was the temp increasing on the display.
     
  18. MrStop

    MrStop Member

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  19. DrDiy

    DrDiy New Member

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    MrStop, how is the HTP water heater working out for you? I'm looking to buy the same water heater for basically the reasons you with them.
     
  20. MrStop

    MrStop Member

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    Still working great! I have noticed a drop in my gas use since the install. However, I think my water use has gone up due to my son taking hot showers for too long now!
     
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  21. Dana

    Dana In the trades

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    Putting the bathroom lights on a occupancy/vacancy sensor switch to time out 10 minutes after the last occupancy was sensed was the cure for "endless shower" syndrome among the teenage population at my house! :) (YMMV)
     
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