Tankless recommendation for a replacement

Discussion in 'Tankless Water Heater Forum' started by yannecantik, Mar 27, 2019.

  1. yannecantik

    yannecantik New Member

    Joined:
    Oct 24, 2005
    Location:
    Minnesota
    My old Thermar tankless water heater gave out recently and I'm looking for a replacement.
    Location is North MN with ground water temp under 40 degrees most days possibly colder during long winter months.
    One shower, no tub, 4 people household.
    I'm looking for min 9gpm or higher, 199k btu, gas unit (propane) but undecided whether I should get a condensing one or non condensing one.
    Is this the right specs for my living situation?
    What brand is better suited for my climate? I was recommended to get a Bosch.

    Condensing vs non condensing:
    1. Which one last longer?
    2. Which one has less issues?
    3. Installation cost, which one is higher and by how much? I'm aware that condensing units cost higher but cost less to install.

    Thank you!
     
  2. Dana

    Dana In the trades

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    Condensing has the advantage of having greater thermal output for the same burner size. The gpm numbers given by numers are all presuming a particular temperature rise that may not be relevant to your application. It's all about the BTU. An input of 199,000 BTU/hr at 95% efficiency delivers 189,000 BTU/hr to the water. At a 70F temperature rise (40F to 110F, a decent bathtub filling temperture) the max flow is 189,000/70F= 2700 lbs per hour, or 45 lbs per minute.

    At 8.34 lbs/gallon that's 5.4 gpm for the condensing unit.

    An input of 199,000 BTU/hr in an 85% efficiency burner deliversd 169,000 BTU/hr to the water, which at a 70F rise is 2414 lbs/hr == 40.2 lbs/ minute == 4.8 gpm for a non-condensing unit.

    Non-condensing tankless heaters require stainless steel exhaust vent piping which is quite expensive. When the venting is that expensive people tend to mount it as close as possible to an exterior wall to keep the venting cost reasonably bounded, but in Minnesota wind coming down the vent can freeze and break the heat exchanger in just a matter of hours when it -10F outside.

    Condensing tankless heaters can use inexpensive plastic piping, and can (and should) be set up to pipe in the combustion air directly from the outdoors. By mounting it where there's at least 10' of vent before it goes outdoors and with the combustion air piped into a sealed unit there isn't much potential for freeze up, since the wind then can't force a backdraft of outdoor air through the heat exchanger.

    There is no question but that a condensing unit is going to be cheaper and better to install in a way that has low freeze-up risk.

    The "Lexus of LP condensing water heaters" would be something like the Rinnai RU199IP. Rinnai is the world's largest manufacturer of gas/LP fired appliances, and headquartered in Japan, but with excellent support network in the US. The "Camry" equivalent would be something like the HTP HydraSmart RTO-199, which is designed manufactured in Korea by Kiturami (a first tier boiler manufacturer), but imported and supported by HTP, a boiler & water heater company in Massachusetts. Competing head to head with HTP/Kiturami (both in Korea and the US) is the Navien NPE-240A. Unlike Kiturami, Navien's North American market strategy was to set up their own support network, along the lines of Rinnai, but it's not as extensive or well developed as Rinnai. The DO have a presence in Minnesota, but I'm not sure how well supported it would be in your part of the state.

    There are others. It all boils down to just how competent the installers are, and how much product support there is in your local area. Bosch support isn't that great near me, but Rinnai/HTP/Navien are all very well supported with local distribution and dozens of experienced installers to choose from. The last thing you want is an installer whose tankless experience is just yours and one or two others before that, who has never taken the factory/distributor training on how to set up and fully commission a big burner modulating unit like that.

    Depending on your propane pricing and showering patterns it might be worthwhile to install a decent sized (4" x 48" or taller) drainwater heat recovery unit downstream of the shower drain. That would cut the BTU/hr requirements of a shower in half, leaving more margin for other uses, and would be enough to down-size to a smaller tankless. The current best-in class is the EcoDrain V1000 series, pushing Renewability's PowerPipe industry from a long held industry dominance (they're not bad either.) At 2.5gpm the 4" x 48" V1000-4-48 returns 57% of the heat back to the incoming water stream.

    At a 65F temperature rise (40F in, 105F at the shower head) a 2.5 gpm (= 1250lbs/hr) shower takes 81,250 BTU/hr. If a heat exchanger is delivering 57% of that heat it is freeing up 0.57 x 81,250= 46,313 BTU/hr of burner output for other hot water use.

    That's the equivalent of adding 50,000 BTU/hr of burner (input) to the unit, but a 50K burner that uses no additional fuel, and has a zero maintenance lifecycle of a handful of decades. With a 4 person showering-only household it'll definitely pay for itself many times over in it's service life, and depending on your propane rates and showering habits that can be in less than 5 years. As a general rule the fattest and tallest one that fits pays off the soonest, due to the higher efficiency outpacing the higher marginal cost of the unit.
     
    Last edited: Mar 28, 2019
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  4. yannecantik

    yannecantik New Member

    Joined:
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    Location:
    Minnesota
    Thank you Dana for the reply. I greatly appreciate the information and recommendation provided.

    I will discuss the recommended water heaters with my plumber.
     
  5. yannecantik

    yannecantik New Member

    Joined:
    Oct 24, 2005
    Location:
    Minnesota
    I figured out yesterday that my old tankless had 100k btu only. I'm not sure about the gpm.

    Would it be a problem to replace it with 199k btu unit?
    Do the gas pipe size and distance from gas storage tank matter on this? I don't want to encounter issues down the line related to this.

    We have a metal vent pipe from the old Thermar non condensing unit. Can this be used with the new non condensing unit?

    The old TWH is vented to the roof. Can we still use the same vent hole (same size and all) for the condensing unit?

    Is is better and a safer bet to get a replacement TWH with specs similar to the old unit?

    I am having a hard time making a decision.

    Forgot to mention that I have a water tank (to hold incoming water from the lake) next to the TWH unit, a whole house water filtration system, and a septic tank (mound). In case these things need to be considered.

    Thank you.
     
    Last edited: Apr 1, 2019
  6. Dana

    Dana In the trades

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    The size of the gas plumbing matters. Most 199K tankless units require a 1-1/4" dedicated gas line from the regulator to the tankless if it were natural gas. But if you're regulating the propane pressure close to (or seperately for) the tankless you're probably going to be OK. Distance to the tank doesn't matter unless the pressure regulator is located at the tank.

    You can't use galvanized B-vent with either at condensing tankless or most 85% efficiency non-condensing tankless. The condensing unit can use plastic venting, the non-condensing requires $tainle$$. You can use the same hole to run the plastic venting , but be sure to air seal every penetration of floors & ceilings. Many/most installations in basements side-vent it through the band-joist, "snorkeling" both the combustion air intake and exhaust pipes upward on the exterior to at least a foot above the historically highest snow depth mark.
     
  7. yannecantik

    yannecantik New Member

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    Location:
    Minnesota
    How do I find out about this? We do have other things that are using propane.

    I am very interested in Takagi T-H3-DV-P. Do you have any experience with it?
    What's Takagi's reputation in general?

    Thank you !
     
  8. Dana

    Dana In the trades

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    Propane regulators typically have these types of form factors, so take a look.

    [​IMG] [​IMG]

    They can be big or small, and many appliances will have a small one built-in or installed next to it, even when the propane lines are already regulated at some other pressure.

    Takagi at one time had a pretty good reputation, but were bought up by another company a handful of years ago. They haven't turned into any sort of disaster since then, but word on the street is that current stuff isn't as robust as the stuff of decades past. I'm not sure how much of that is rose colored glasses vs. verifiable reliability data though.

    The US support network is quite good, and unlike most vendors the tech support line is willing to talk homeowners through diagnosing and fixing problems, even if the rumor turns out to be true that current product isn't as bulletproof as prior models. The warranty terms are reasonable, and the product support is there, so there's no reason to avoid them.

    FWIW: I've heated my house for about a decade now with a Takagi KD20 tankless as the hydronic heating boiler, and it's been VERY reliable. I expected it to be toast by now at the duty cycle it's been running, but it hasn't needed a single repair or adjustment other than to clean the tiny screen filter once or twice per year (or more recently, a dozen times in one week after installing a rusty used radiator on one micro zone.)
     
  9. yannecantik

    yannecantik New Member

    Joined:
    Oct 24, 2005
    Location:
    Minnesota
    Thank you for your reply.
    The prices are VERY reasonable for Takagi units. It's a big selling point for me. Not to mentioned that it's lighter and smaller.

    More questions:
    Newer units need electricity (vs Thermar). Am I looking at a costly wiring cost in association to this?
    There's an outlet nearby. I hope that I can just plug the unit in.

    One of the recommended accessories for Takagi TWH is the neutralizer to neutralize acidic water. It's recommended for septic tank owner.
    Is this worth installing?

    What other accessories worth considering for this unit? Pumps?

    Does 199k btu unit use more gas/propane?

    Thank you.
     
    Last edited: Apr 2, 2019
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Retired Systems engineer for defense industry.
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    Unlike say an electric water heater, the tankless unit is just powering the electronics and maybe a pump, so it shouldn't require any rewiring...an existing receptacle should be fine. Don't know if it has a plug, but even if it doesn't, it's probably 120vac. You can probably download the installation and operator's manual, which should show the process and what's required, even if you don't do it yourself.

    I'd consider adding the neutralizer. The bacteria in your septic system will be healthier.

    The burners on most of these modulate to adjust to the flow. If you ask for a higher volume, then yes, in that instant, it will be using more fuel. But, if your flow doesn't change, the burner may just modulate down to that 100K or even less, depending on the demand. A larger burner will allow a higher volume of hotter water, but that doesn't mean you will always be using it.
     
  11. Dana

    Dana In the trades

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    jadnashua has it right- the power draw is less than 200 watts peak (it peaks when the exhaust blower is running a flue purge), and can be plugged into any grounded 120VAC circuit.

    The amount of propane it uses is based on how much water you heat, up, not the maximum firing rate of the burner.

    The fact that it's a condensing burner and can modulate to a much lower output than any Myson Thermar means it will use less propane than your older non-condensing unit.

    Yes, a condensate neutralizer is a good idea.

    As for other accessories...

    Adding a drainwater heat recovery heat exchanger for the shower can cut propane use DRAMATICALLY , and would pay for itself fairly quickly with four people showering daily unless you have the cheapest propane in the US.

    [​IMG]
     
  12. yannecantik

    yannecantik New Member

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    Oct 24, 2005
    Location:
    Minnesota
    Thank you.
     
  13. yannecantik

    yannecantik New Member

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    Location:
    Minnesota
    Thank you!
    I checked the prices on drainwater heat recovery units. They're pricey!
    Thank you for the recommendation.
    Right now I fill up propane once a year at most twice a year. Might take a long time to get a return of my investment this way.

    My plumber is not familiar with Takagi .
    But he's familiar with my set up because he installed the Thermar some years ago.
    He's also very experienced and has been a plumber for a long time.
    We don't have a lot of options when it comes to plumbers in my small rural town.

    Should I go ahead with Takagi or get a brand that is familiar to my plumber?

    If you were living in a rural area without good support of any TWH manufacturers, what brand would you pick and why?

    Thank you!
     
  14. Dana

    Dana In the trades

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    Purchased direct from the manufacturer you can get a drainwater heat recovery unit with greater than 50% return efficiency for under a grand, and it's often a DIY-able installation. The best bang/buck right now is the EcoDrain V1000 series, but the Renewability PowerPipe series isn't bad either. (If you're close enough to the border you might be able to get it cheaper buying it in Loonies rather than Greenbacks.)

    Some of the return on investment of the heat recovery unit COULD be a smaller cheaper tankless, since the showering performance is effectively doubled with the heat exchanger.

    A "fill up" isn't a standard quantity- tanks come in all sorts of sizes. How much do you SPEND on propane per year? If showering accounts for more than half your propane use (likely, unless you are using propane for space heating), the drainwater heat recovery is going to save more than a quarter of the bill.

    [​IMG]

    Regarding models with minimal support in the north, how far is it to the nearest Home Depot?

    The Westinghouse WGRTLP150 or WGRTLP199 are decent. Westinghouse markets the same water heaters under the paint as HTP's all-stainless condensing tankless water heaters (some Laars, Rheem & Noritz models are identical too), and you would be able to get warranty support from both the store and Westinghouse. With just one shower and no tub the -150 would have sufficient capacity. Whereas the 100K Myson Thermar had only about 80,000 BTU/hr of output at max fire and couldn't support much more than a single shower flow with any margin, the WGRTLP150 delivers over 140,000 BTU/hr-out at max fire, which is plenty of margin for a 1 bathroom house. The -199 would only be important if it were a 2-3 bathroom house.

    Like the Bosch Greentherm C units they have a 10:1 turn down ratio (I think the Thermar was only good for what- about 2.5:1 ?) and can run reasonably low flow rates with good temperature control. The intake and exhaust ports are separate rather than concentric on the Bosch, so generic plastic venting can be used rather than a custom concentric kit.
     
    Last edited by a moderator: Apr 6, 2019
  15. yannecantik

    yannecantik New Member

    Joined:
    Oct 24, 2005
    Location:
    Minnesota
    Thank you.
    I will look into the drainwater heat recovery units that you recommended.
    I pay less than 500 for each propane fill up.

    I live 3 hours away from the nearest Home Depot.

    People who do installation and repair are local individual plumbers.

    I am stubborn and still want to get the Takagi. Unless there are other good reasons not to.
    I like the copper heat exchanger on Takagi unit. What are your thoughts on this?

    Thank you!
     
  16. Dana

    Dana In the trades

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    The dual heat exchanger approach (one copper, one stainless) that Takagi uses adds complexity while reducing the unit's size and material cost for the manufacturer. Adding a secondary stainless heat exchanger was also a way to take an existing tankless design and convert it into something that condenses, pretty common 10-15 years ago. Other manufacturers who did it that way in the past (notably Navien - their NPE-180S or -180A is another good bet) have evolved toward stainless-only heat exchangers, but others (notably Rinnai) still have copper primary heat exchangers.

    [​IMG] [​IMG]

    Stainless-only heat exchangers are more rugged against condensation than copper, but it's possible to design around that weak point. Takagi was fairly late to the condensing water heater game, years behind their competitors, but they've been at it long enough that their designs should be well-evolved by now.

    With the Navien tankess water heaters you don't need to sweat the fuel pipe sizing as much- they have proprietary ways of making it work with smaller pipe even when the pressure is marginal.

    At $500/fill up averaging 1.5x per year you're spending $750/year on propane. If the drainwater heat exchanger sets you back a grand and saves ~25% on your propane use it's paid off in about 5 years. How are your other investments doing?

    If my 401K had that kind of internal rate of return I could have retired decades ago!
     
  17. yannecantik

    yannecantik New Member

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    Minnesota
    Thank you Dana for your replies. Really helped me! I bought the stuff that I need. Have a great day!
     
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