Tankless installation questions

Discussion in 'Tankless Water Heater Forum' started by partnerinflight, Dec 20, 2017.

  1. partnerinflight

    partnerinflight New Member

    Joined:
    Dec 20, 2017
    Location:
    Seattle
    So got myself into a bit of hot water (forgive the bad pun), was hoping the fine folks here could help with some know-how.

    So I bought a Rinnai RUR98iN tankless water heater online. Due to a confluence of bad luck and stupidity, I contracted an HVAC company to install the thing, even though they weren't an authorized Rinnai dealer. Upon examining their installation, however, I was a bit horrified. Here are the things I noticed -- please tell me whether each one of the following "issues" is actually an issue, and if so, how severe.

    For clarity, the water heater is installed in the garage of a 2-story single-family house.

    1. No Pressure Release Valve installed. (I already called and complained, and they came out and fixed that.)

    2. Hot air vent is a 3" PVC pipe going outside. No kind of termination or even a grate installed on the end. (They said that's normal -- but seems crazy to me -- what if birds get in there?) I bought a cheap plastic grate at Home Depot and put that in, but am concerned about it restricting air flow. Should I spring for a real termination, a la https://www.supplyhouse.com/Rinnai-223176PP-12-Horizontal-Condensing-Termination-Kit-w-Elbow?

    3. Water drain pipe comes out the side of the house, likewise not terminated in any way. It's about 2 inches off the ground -- should I be concerned about snow plugging it up? (If so, any way to fix without totally reinstalling?)

    4. This is the one that really worries me: they took the cap off the air intake on the heater, but did not put any kind of a pipe in there. When I asked about that, they said because the water heater is in the garage there's no need for any kind of piping. Is this true? I'm concerned about something accidentally falling into that hole and ruining the water heater. Should I put a grate on there or something?

    5. No thermal expansion tank installed. They said for tankless heaters they're not needed. True?

    Thanks in advance!

    P.S. Same company also installed a Trane furnace, and also left the 2" heat vent pipe sticking out the side of the house. Is this supposed to be normal? If not, think it's worth complaining to Trane? (These guys are supposed to be Trane dealers)
     
    Last edited by a moderator: Dec 23, 2017
  2. nakopf

    nakopf Nailed it.

    Joined:
    Nov 23, 2017
    Occupation:
    Plumber
    Location:
    Bellingham, WA
    1. Fixed

    2. We install bird/bug screens on our terminations, but they're not required. That termination kit you posted is for concentric venting, so it wouldn't do much good for your installation.

    3. There should be a 3/4" pressure relief drain and a 1/2" condensate drain. Either or both can terminate outside, and what you described sounds correct. If there's only one drain, there might be an issue - a picture of the bypass valves (bottom of the unit) would help.

    4. Incorrect. Rinnai wants intake and exhaust to same atmosphere (both outside). The intake should roughly parallel the exhaust and terminate nearby (clearances are in the manual). Alternatively, a single concentric intake/exhaust pipe can be run using the termination kit you linked.

    5. Technically, yes, a thermal expansion tank is required, but there's debate as to the necessity and I've seen RUR units with large recirculation loops work well without thermal expansion tanks.
     
    Last edited: Dec 21, 2017
  3. Sponsor

    Sponsor Paid Advertisement

     
  4. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The condensate drain outdoor can potentially freeze solid during an extended cold snap (even in balmy-winter Puget Sound region). It's also slightly acidic, and can create localized spalling degradation if it's dripping on concrete, unless diluted regularly and rapidly by rain water (a given in winter in your area, but not necessarily in June/July). Draining it into a standard air conditioner condensate pump that then pumps it into a sink or other drain that's used regularly would be fine. If it's being dumped into a rarely used drain is should be run through a neutralizer cartridge first.

    The open ended vent is fine, but so is putting a grille on it. If the air in the garage is dusty, dirty or has any sort of chemical vapors gardening fertilizers/pesticides or gasoline vapors, it's prudent to draw the combustion air from the outdoors.

    If there is a pressure reduction valve or backflow preventer on the water intake to the house a small expansion tank is a very good idea. If there isn't, it's not really necessary. The volume of heated water in the Rinnai and the hot water distribution plumbing is miniscule compared to that of a tank type water heater.
     
  5. partnerinflight

    partnerinflight New Member

    Joined:
    Dec 20, 2017
    Location:
    Seattle
    Thanks guys! So the garage air is fairly clean; what sort of a risk do I run leaving the air intake as is?

    The condensate is dripping down onto earth/gravel. Is that an issue?

    How much clearance do I need between the end of the condensate pipe and the side of the house? I'd love to put some kind of a flushing thing up against the sidewall, so it's not just a white PVC pipe protruding out of an otherwise gray-painted house... Also, can I paint the PVC pipe to match the house color?

    Uploaded the pics of the install.

    Thanks again! Feeling a bit better... at least that the house is not eminently going to explode or catch on fire. ;)
     

    Attached Files:

  6. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Dumping the condensate onto the gravel in rainy Seattle isn't a big deal, but a frozen condensate drain can be.

    If air intake is wide open, staring at the ceiling, at the VERY least it should have shepherd's staff hook of PVC so that gravity doesn't deposit things in there, and put a screen on it to keep moths & ants out. One wayward leaf that flys up when the garage door opens could become a real PITA if it gets sucked in, and with the intake pointed up there will be some amount of grit falling in over time.

    It looks like the gas feed to it is only 1", not 1.25", and it's next to a condensing gas boiler(?), which is perhaps teed off the same gas line? In general 199,000 BTU/hr modulating burners like a tankless need a home-run dedicated line back to the regulator/meter without other appliances sharing the run to operate consistently. The total BTU load on the gas line might be over spec for it's length (including "equivalent lengths" of all the ells & tees in the path from the regulator", which is something to figure out sooner than later.

    The chart below is in 1000s of BTUs:

    [​IMG]

    Assuming the boiler is at least 60,000 BTU/hr at maximum fire and 1" pipe, it has to be no more than ~20' (equivalent lengths + straight sections) from the regulator. If the boiler is bigger than that, it needs to be more.

    [​IMG]

    There may also be an issue with the overall capacity of the meter, if there are multiple big-burner appliances feeding from it.

    I'm not crazy about the kink in the flex gas line with the tape on it either. Hopefully you've inspected it closely and there are no signs of metal fatigue(?).
     
  7. partnerinflight

    partnerinflight New Member

    Joined:
    Dec 20, 2017
    Location:
    Seattle
    Thanks for the detailed response!
    The appliance next to the water heater is an electric steam humidifier -- it has no gas line feeding it. The line currently runs only to a Trane furnace, and the water heater. (There's another line running to the kitchen for a gas stove, but we're not using it right now.)

    The yellow flex hose was just installed two days ago. What should I look for, in terms of the metal fatigue?

    Re line length -- if the line is over spec, what's the implication? I.e. appliances simply don't work as well? Get damaged? Explosions?

    Bottom line: do you think I should contract someone who actually knows what they're doing to come repair this whole mess? Or is this something I can conceivably fix on my own? (zero HVAC experience, but I've replaced a few light switches, and work as a software engineer. Hopefully not a too terribly dumb one.)

    Thanks!
     
  8. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    It's a little hard to tell visually, but if the flex line has been flexed too hard in that kink it'll be less flexible or springy than the rest. I'm not totally sure what the minimum allowable bend radius is on that type of line, but it looks like a pretty sharp turn. These folks specify greater than 3" bend radius for 3/4" line, yours looks like less than 2":

    [​IMG]

    A coffee mug has a radius of about 1.5", and it doesn't look like the one on my desk would snug into that arc, not even close!

    Normally it would have enough extra to allow for some mechanical compliance/flex in the event of an earthquake, etc. If it flexes or pulls hard enough to create even a tiny crack, you may end up with something like this (after your garage gets scattered all over King County):

    [​IMG]

    Take a good hard look at it- measure the bend radius if you have to. A t

    What's the BTU rating on the Trane? Is it teed off in the middle of the run to the tankless, with the tankless on the far end (or conversely)? Sketch up the diameters and lengths to any branches, and what they're feeding (BTU-rate wise) at each branch point from the tankless all the way back to the regulator at the meter.

    If the tankless is running when the furnace burner kicks on the sudden drop in gas pressure may be sensed as an error by the tankless controls and it can shut itself down, and won't fire up again until someone resets it or cycles the power. (I'm not sure if error codes are stored semi-permanently on that unit or not.) Sometimes interactions with other large BTU appliances cause a tankless to regulate temperature less well. If there's simply not a fat enough supply it can shut itself down at higher firing rates, even without interactions from other burners.

    Take the time to go over the installation manual in detail- make it your bedtime story for awhile, see if there's anything else amiss.
     
  9. partnerinflight

    partnerinflight New Member

    Joined:
    Dec 20, 2017
    Location:
    Seattle
    Thanks for the responses! You don't by any chance work in the Puget Sound area? :) If so, how much do you think it'd cost to fix the gas line situation?

    You're right -- the water heater gas line splits off the same line leading to the Trane. The furnace is S9V2B080D4PSAA -- I'm not exactly sure where to look up the BTU. Is that the "80"?

    I'll measure out the total pipe length today and get back.

    So for the equivalent lengths chart -- do I read correctly that for a 1" pipe, a 90 degree L is the equivalent of 5.2 feet of straight pipe??? That's... er... crazy!! (not doubting, just shocked. :))

    Thanks again!
     
  10. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The equivalent lengths are correct. The turbulence of the 90 degree turn is the friction-equivalent of 5' of straight pipe.

    The "080" in the middle of the model number is the BTU-in, indicating 80,000 BTU/hr.

    Given that the average heat load of a 2500' house in Seattle is usually under 25,000 BTU/hr, and often under 20K, that's a heluva oversize factor, but that's for another time.

    Is it really 1" hard-piped gas? That's pretty skinny for a 199KBTU/hr tankless even without the 80K gas furnace off the tee.

    I'm not licensed plumber, let alone certified gasfitter, but I'm only about ~50 driving hours from any Seattle location (I've done it in as little s 53 hours, total elapsed time.)
     
  11. partnerinflight

    partnerinflight New Member

    Joined:
    Dec 20, 2017
    Location:
    Seattle
    Thanks Dana. Merry Christmas! Yes, I think 53 hours might be a wee bit of a drive. :) So yeah, the total length with all the Ls is closer to 40'. Empirically everything appears to work ok (although today I turned on several hot water outlets at the same time, and the water went freezing after 5 mins or so), but I've contacted the company you referenced to come check everything out.

    Re oversize factor -- confused. I did talk to several HVAC companies, and the price range they quoted me was if anything more than what these guys charged for the furnace. (Paid $2800 for the Trane plus install.)

    What's the implication of the oversize -- more gas usage overall, or just higher initial upfront cost?

    The line is 1" hard-pipe, although the connection to the furnace is 1/2" flex-hose. (at least I think it's 1/2 -- it's even smaller than the one to the tankless.) I've never seen stage 2 kick in on the furnace... maybe that's why? (Although so far stage 1 has been more than enough.)

    Thanks again!
     
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    When a furnace or boiler is oversized for the load in the house, it only runs for a short time, then shuts off, then, needs to start up again. This causes multiple problems:
    - efficiency is determined by steady state operations - when you start things up, it takes a bit to reach full efficiency and then, once you get things all warmed up, it shuts off, wasting heat that just goes up the flue
    - increased cycles tend to wear things out faster - have you ever had a light bulb go out while it had been running? They almost always fail just when you turn one on...steady state helps. Just like lots of short trips in your car are not good for the muffler and oil, they aren't for your heating system.
    - they cost more up front
    - by causing the multiple on/off cycles, the comfort isn't as great as having the system running more frequently, keeping the dwelling at a more consistent temperature. Ideally, it could run constantly, just putting out enough heat to overcome that lost to the outside, but that is really hard to achieve. Right sizing can get closer.
     
  13. partnerinflight

    partnerinflight New Member

    Joined:
    Dec 20, 2017
    Location:
    Seattle
    Thanks Jim. So if the furnace overall is 80k btu, then how much does just stage 1 consume? Looking at Nest history, it looks like the furnace has run in intervals from 20 mins to about 3 hours over the past couple of days... of course it's been uncommonly cold here, so that may have been why.
     
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    A multiple stage furnace can help. Excess capacity can help if you like deep setbacks, since there's excess heat available to more quickly bring the structure back up to your set point. a 20-minute burn is decent...things get messy if it is more like in the 3-minutes. Ideally, it could run constantly, but the variations in need can be huge, and most systems just do not have the ability to modulate through a huge range.

    You'd have to look at the spec sheet for the furnace you have to see what the output is for stage 1 and stage 2. A good heat load analysis is likely to find your real needs are more in the 30-40K BTU range than 80K. Note, you need to determine if that's input BTU, or output. The more efficient the unit, the less is lost in the process. Some of the best ones are in the mid-90% range...older ones, especially if they short-cycle, could be in the 60-70% range.
     
  15. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The low thermal mass of hot air furnaces means they don't lose much if any efficiency to oversizing, since there is only a small amount of "abandoned" heat to lose as standby loss after every burn cycle. If the minimum burn time is 10 minute you're golden, from an efficiency point of view. A 3 hour burn is probably from a deep overnight setback on a cold night(?).

    From a comfort point of view cycling 0n/off during cold weather can lead to some rooms seeing large swings in temperature, too cold in the minutes before a cycle too hot at the end of a burn cycle. The higher cubic feet per minute air volume of the larger than necessary air handler also imparts and air chill, and more noise.

    If you want to know your actual heat load, run a fuel use heat load calculation on some wintertime gas bills, but only for periods where there was a consistent and substantial heat load, say December through March, not during the shoulder seasons when hot water use can skew the result due to a low/very low duty cycle on the furnace. There is no point to retiring a 3-4x oversized furnace that's still functional, but when it's time to replace it, knowing the actual heat load and sizing optimally (< 1.4x oversize factor) makes it more comfortable overall.

    According to the pipe sizing table on p.47 of the Rinnai manual with 40 equivalent feet of pipe you should be good for 243 cubic feet per hour (~1000 BTU per cubic foot), which you are clearly above when the furnace is factored in.
     
Similar Threads: Tankless installation
Forum Title Date
Tankless Water Heater Forum Opinion on installation for Rinnai Tankless? May 17, 2019
Tankless Water Heater Forum Tankless installation positioning Aug 16, 2018
Tankless Water Heater Forum Paloma PHH-32DV condensing Tankless water heater installation Jan 18, 2012
Tankless Water Heater Forum Tankless WH using cistern water Yesterday at 2:19 PM
Tankless Water Heater Forum Tankless venting Jul 6, 2020

Share This Page