Replace Lochinvar Squire Indirect Water Heater with Tankless system?

Discussion in 'Water Heater Forum, Tanks' started by eoren1, Jan 13, 2019.

  1. eoren1

    eoren1 New Member

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    Aug 20, 2005
    Location:
    Massachusetts
    Forgive the newbie question but would really appreciate thoughts from those with far more expertise than me (homeowner).

    We purchased our home in Massachusetts in 2010 and, as part of the renovations, installed a Lochinvar Knight boiler and Lochinvar Squire 52 gallon indirect water heater. We have 3 zones of baseboard heating in the house (though one zone is basement which almost never turns on).

    With a now 11 year old girl and 13 year old boy and everyone taking showers/baths at the same time each night, we are running out of hot water not infrequently. We have two bathrooms - girl and wife prefer baths; boy takes 20+ minute showers...

    I figured my options are to either get a larger indirect water heater or a tankless system. I am favoring the latter to also minimize or eliminate the risks of the water tank giving out and causing a flood.

    The tankless system I was looking at was the Rinnai RUR98iN. I checked and cold water temp right now is 47F so I figured I would need that systems 5 gpm for 75 degree change plus the recirculator option to be able to sustain good volumes of hot water.

    So my questions are:
    1. With the Lochinvar Squire installed in Nov 2010, am I approaching its end-of-life? I thought all water tanks were good for about 10 years.

    2. Would a tankless system be a good option for us and can it be used with my current setup? In other words, does the Lochinvar Knight continue to heat the house (even without the indirect water tank) and the Rinnai takes over for hot water duties? [told you I'm a complete newbie]

    Appreciate any and all input regarding the above and other options I maybe should consider.

    Thanks!
     
  2. Dana

    Dana In the trades

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    The Squire should have another decade left in it.

    For less money than a new indirect or worse, a combi boiler, think about installing the tallest 4" EcoDrain V1000 that fits. There are other vendors, but this is a 4th generation product with highest return efficiency and the lowest pressure drop. A 4" x 48" or taller will more than double the "apparent capacity" of any tank type water heater, and without burning more fuel.

    [​IMG]

    Cheaper still will be very low-flow sh0wer heads.

    Before diving into a combi boiler, do the napkin math on your radiation vs. the minimum fire output of the boiler, which may (or may not) be higher than your current boiler. If you don't have enough radiation on each zone to emit the full boiler output at condensing temperatures you may be forced to run at a less efficient water temperature. (If experience is any guide there's at least even-odds that you're already in that situation with the existing boiler, but there's no financial case for retiring it early.)
     
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  4. phog

    phog Member

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    Hi Dana, I notice that the poster has two bath takers in the house, which I would guess is the biggest factor in the hot water running out. It seems like filling two tubs daily around the same time that two others are trying to shower is a recipe for at least one person getting left "in the cold". Wouldn't this be the ideal situation for a tankless?

    With tankless handling water heat, ideally the boiler would also be downsized to account for the lower base load minus the indirect. But if the overriding goal is not running out of hot water, and there isn't budget for a right-sized boiler, is it really that bad a situation to split off the water into a tankless?

    Alternately, perhaps a smaller tankless pre-heater (or post-heater) in series with the indirect would be more cost effective?
     
  5. Dana

    Dana In the trades

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    "...boy takes 20+ minute showers."

    That alone make the V1000 "worth it", but whether it provides enough relief to work kinda depends.

    Increasing the storage temp on the indirect, and reviewing/adjusting the settings on the Knight to optimize hot water service at the new higher storage temp might do it too.

    Putting an occupancy sensor on the bathroom light set to turn off the lights 10 minutes after occupancy was last sensed can make a difference too.:)
     
  6. eoren1

    eoren1 New Member

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    Thanks everyone!

    The EcoDrain is an interesting concept - just not sure how we would access either drain to install it. We live in a 1950's house that we have nearly completely remodeled and just put in an addition. The drain for the shower goes through the wall behind the TV in the family room...

    On the other hand, the addition holds the more important bathroom (ours) and I am now wondering about using an electric tankless heater just for that room. This question might be better aimed at the other subforum but would love your initial thoughts on it.

    The addition was built with a 5' crawlspace connected to the basement. There is easy access to the Pex tubing leading up to the bathroom. No gas piped into the addition so electricity would be preferable (and would mitigate need to exhaust which is a bonus). The shower has a 2.5gpm head so would need to keep up with that rate. There is also a washing machine in that bathroom and a full tub...

    Oh and I've tried manually turning flickering on/off the lights to the kids' bathroom (main switch is outside) and that has shaved maybe a minute of the boy's typical time. At least the kid showers...
     
  7. Dana

    Dana In the trades

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    An electric tankless is an ABYSSMAL choice for anything at MA style incoming water temps. The dumb math goes:

    2.5lbs/min x 60 minutes x 8.34lbs/gallon = ~1250 lbs/hr.

    With 105F at the showerhead and potentially 35F incoming water it's a 70F rise.

    70F x 1250 lbs/hr= 87,500 BTU/hr

    Converting that to watts is 87,500/3.412 = 25,645 watts. At 240VAC that's 107 Amperes. You'd need at least a 27-28kw electric tankless. You'll need to an "extra" 125A to 150A/240V of electric service and some wire fat enough to haul the SUV out of a ditch to hook that up.

    And that's without even addressing the abuse the high current intermittent load is delivering to the distribution grid in the neighborhood. (You can see the power lines jump if you turn the hot water on full blast quickly enough!)

    Bottom line, an electric tankless is the least green and lowest performance option imaginable!

    A lowboy electric tank can fit into the crawlspace and has none of those problems. A 47 gallon Rheem XE47SB06ST45U0 is only 36" tall, the 50 gallon XE50M06ST45U1 is 48" tall. There are others. Size it for the biggest tub it has to fill.

    With a 5' crawlspace you have enough room for at least a 36" or maybe even a 48" drainwater heat exchanger. Last time I looked EcoDrain wasn't on the pre-approved MA plumbing components list, but you can probably get a variance. Worst case, Renewability's PowerPipe series are MA listed, and they're not bad for either pressure drop or return efficiency, though at 2.5gpm the return efficiency is still a hair under 50% for the 4" x 48". (I've have a 4" x 48" PowerPipe on my system at home for the past ~10 years. Anticpated lifecycle is 40+ years before it's performance has fallen to 75% of what it was when new, but the informal measurements taken recently are still pretty much where they were in late 2008.) The 4" x 36" V1000 has a return efficiency a hair over 50% (it beats the 48" PowerPipe!)
     
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  8. phog

    phog Member

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    eoren -- can you share with us what exact model # your Knight boiler is?
     
  9. eoren1

    eoren1 New Member

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    Wow! Thanks for the math Dana. Had no idea it would take that much electricity.

    I'll post the Lochinvar Knight boiler model when I get home.

    Guess the options now are:
    1. Figure out how to up the temp of the water in the Squire - guessing that is set by the Knight boiler but not sure if there is any concern with upping the temp besides the obvious burn risk. With an 11 and 13 year old, I think that risk is lower and manageable.

    2. Purchase a second indirect tank to place either in series with the current 52 gallon tank or in the crawlspace of the addition.

    3. Replace the Squire with a much larger tank but that seems like a waste if it would last another 10 years.

    4. Pipe gas to the addition and run a gas-powered tankless for the addition bathroom.
     
  10. phog

    phog Member

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    A couple comments on your options.

    First, as Dana mentioned perhaps the simplest thing to try would be adding a tempering / thermostatic mixing valve to your existing tank & upping the storage temperature. The tempering valve will take the scalding hot water from the tank and mix in some cold water to reduce down the temperature before sending it out into the hot water plumbing. It really can make a big difference in the overall performance of your system. With increased temperature you can get increased mineral scale buildup inside the tank though. Just something to think about.

    If upping temperatures isn't enough, we would then need to know the output of your boiler so we can figure out if you already have enough spare capacity to drive a larger (or second) indirect tank. If you can tell us a bit more about the rest of your house it would help too -- square footage, and if you know anything about the construction type, 2x4 vs 2x6 walls, insulation type etc. Build date can be helpful too.
     
  11. Dana

    Dana In the trades

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    No we don't. The boiler doesn't need "...spare capacity..." for running a bigger indirect. This isn't a commercial application with a high duty cycle on the indirect.

    For a residential application even a pretty crummy house with a boiler 1.25x oversized for the 99% heating load would have no problem handling a 100 gallon indirect zoned priority. Even the smallest Lochnivar Knight (KB-081, with over 75,000 BTU/hr of output) has more boiler output than a typical 75 gallon standalone water heater's burner, and recovery times would still be reasonable even at 150 gallons- not long enough to be a comfort issue while waiting for the water heater to be satisfied.

    Far more import data points would be the total baseboard length per zone, zone by zone. That would establish both an extreme upper bound on the design heat load, and would tell us if the boiler would be at short-cycling risk.

    For at least a decade water heaters in MA are required to have tempering valves or thermostatic mixing valves at the output to mitigate the scald risk. I'd be pretty surprised if the Squire isn't already outfitted with one, but that should be verified before cranking it to 150F or something.

    Occupancy sensor switches that turn on when occupancy is sensed and off after a (settable) time out are less than $30. If the kid can't stand showering in the dark he can step out or wave his arm to retrigger the light, but it's proven effective at my house.

    There are several decent sub 2.5gpm showerheads out there. Most people don't get bothered until the flow is under 1.5gpm. The drainwater heat recovery units are efficiency tested at 2.5gpm, but the return efficiency is measurably greater at 2 gpm or less.

    Even in a finished room you probably won't have to demo and repair more than one stud bay to go with a drainwater heat exchanger. A 3" PowerPipe has an outer diameter of 3.75", and fits in a 2x4 partition wall stud bay with only modest sculpting of the wallboard. A 2" power pipe is 3" o.d., and fits in a stud bay with 1/4" of clearance to the wallboard on each side. The five foot R3-60 has a return efficiency of about 53%, the six foot R2-72 has a return efficiency of about 52%. The biggest(fattest and tallest) one that comfortably fits is the "right" one, the marginal increase in efficiency being better than the increased marginal cost.
     
  12. eoren1

    eoren1 New Member

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    Aug 20, 2005
    Location:
    Massachusetts
    Just got home.

    Lochinvar Knight KBN106
    Jotted these down from the digital display just now:

    System temp 108-110 (changed as I was there)
    Tank 130-133 (130)

    While it read as BLOCKED (changed by time I was done scrolling):
    Inlet Temp 159
    Outlet Temp 165
    Flue Temp 183

    I can measure out linear feet of baseboards if that will help

    We live in a house built in 1958 in Marblehead, MA. Have re-sided the entire house and added blown-in cellulose to sides. The finished basement, entire addition and attic have closed cell spray foam. All new Andersen windows. So house is as tight as it'll ever be...

    I don't think the Powerpipe will work for now. The wall that would. need to be accessed is behind the TV and part of a built-in entertainment section with closed cell spray foam put in

    Might be feasible if we ever redo the kids' bathroom but that's not happening soon.

    I texted my plumber and he suggested adding a mixing valve - guess we don't have one now

    Thanks!
     
  13. eoren1

    eoren1 New Member

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    Spoke to the plumber - we do not have a mixing valve now.

    He is going to install one and get tank up to 145 and valve at 125 which hopefully will do the trick.
     
  14. eoren1

    eoren1 New Member

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    One last question - any thoughts on thermostatic mixing valves? Not sure which my plumber uses but did a search elsewhere and found Caleffi were highly regarded and really like the ones that have a built-in gauge which I presume I could adjust to find the optimal temperature.

    If the Caleffi is the best valve out there, can you recommend a particular model? I read this thread and ended up over my head - https://forum.heatinghelp.com/discussion/151809/thermostatic-mixing-valves
     
  15. Dana

    Dana In the trades

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    Caleffi makes good stuff, but Honeywell and others make pretty good thermostatic mixing valves too. I'm less partial to the brand than the specifications. If you're anticipating high flow (10 gpm+ ) compare specs on the pressure drop at different flow rates. Sometimes it's worth bumping up to a 1 incher from 3/4" , especially if your static water pressure is 40psi or less. It sounds like you have plenty of room for raising the temp to get better hot water service out of the indirect. Most indirects can tolerate 180F storage temps, but the most you can reasonably get into the tank out of the KBN106 would be about 160F, but that should be plenty.

    The "...optimal temperature..." out of the mixing valve would be about 115F. That should be able to deliver piping hot 110F water for tub fills at less risk than 120F water.

    The optimal storage temperature for the indirect is the minimum temperature needed to not run out of hot water, which will be primarily a function of your tub-filling patterns. The KBN106 has enough burner to cover a continuous 2.5 gpm shower 24/7/365 with capacity to spare, provided it's set up properly with the indirect.

    At minimum fire at ~ 95% combustion efficiency water temperatures (~120F average, 125F-out, 115F return the KBN106 is dumping about 20,000 BTU/hr into the system. For typical fin tube baseboard it takes about 100 feet of baseboard to emit heat at the same rate. Do you have 100' of baseboard per zone? If a zone's baseboard is significantly shorter than 100' it's going to cycle on/off during extended calls for heat unless other zones are calling for heat at the same time.

    If the burn times when cycling on a zone call are short (way under 200 seconds) and it doing significantly more that 5 burn cycles per hour (say 10 cycles of 120 second burns) it's putting a lot of wear & tear on the boiler and burning up a lot of efficiency too. If that's what's going on in your system it's worth doing something about it. Most Lochinvars let you program how far above the outdoor reset's setpoint it will go before cutting the flame, and how far below that setpoint it refires, which can help quite a bit, but that's not going to fix it for a 50' zone.

    FWIW: I live in 2400' house a 1920s vintage 2x4 framed house in Worcester with mostly original windows + clear glass storms, and an unfinished but insulated 1600' basement. Suffice to say it's WAY below current code for R-values and U-factors. The output of the KBN106 at high fire can theoretically heat my house to 70F when it's -100F outside(!).

    The coldest it's been in the 25+ years I've been here has been about -15F, so it would be overkill for my house, and probably yours too. The fact that it's minimum fire output is more than half my design load (at Worcester's 99% outside design temp of +5F) means it would be a sub-optimal fit- cycling more than modulating with load even with a perfectly tuned outdoor reset curve and enough radiation per zone to emit the full min-fire output at condensing temps.

    If you want to estimate your actual heat load, run a fuel-use based load calculation using wintertime-only gas bills (to reduce the error of solar gain and hot water use.) Most people are surprised at just how low their actual loads are. At least they didn't load your house up with a 150,000 BTU/hr or bigger boiler, but for 19 houses out of 20 the KBN081 would have been more than plenty, and the KBN081 only needs ~75' of baseboard per zone to run it at 120F AWT without cycling.

    Odds are pretty good that if/when the boiler needs to be replaced you can down size it pretty dramatically, and run it at condensing efficiency. When the entering water at the boiler is above 125F the best you're going to do is 87%. When it's entering the boiler at 115F or lower and the boiler is firing it's in the mid-90s.
     
    Last edited: Jan 14, 2019
  16. phog

    phog Member

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    Hi Dana, respectfully, yes we do. The question being asked is not how to correctly size a boiler for optimal cost efficiency. It is how to best achieve a hot water drawdown of around 225-235 gallons within a short time period.

    I get this 225-235 gal number by assuming two 80 gallon bathtub fills + 30min of showering @ 2.5 GPM. We need to know how big the existing burner is to come up with a solution to this problem; without the maximum net heating power we're just guessing.

    Let's say for the sake of argument that the target drawdown period is 1hr. Assume 40F incoming water temp & 160F tank temperature setting with a thermostatic mixing valve set to 110F. This gives an apparent tank capacity of around 77 gallons water storage (assuming 86% first draw capacity off the tank).

    So, in addition to the tank storage we have to produce an additional 148-158 gallons of 110F hot water over the course of the hour. With 70F rise (from 40F incoming service) this means 86k BTU/hr burner output. I'm not sure these numbers are completely representative of the real conditions at this residence, and my math probably needs to be checked, but they're at least in the ballpark.

    With the 75k BTU/hr KB-081 boiler you mentioned, this hypothetical 1-hr drawdown would not (quite) be able to be met, at least with the 52gal storage tank. The even smaller KHN-055 Knight series boiler (51k BTU/hr) would not even have a chance.

    Of course you are correct to point out that the system efficiency is another critical consideration. But I think only the homeowner is in a position to judge the tradeoffs and it is up to them whether (or how much) less performance they can live with than in my hypothetical, to gain cost efficiency.
     
  17. eoren1

    eoren1 New Member

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    Massachusetts
    Dana and Phog - just measured and we have 55 linear feet in each zone (first floor and second floor). Basement has less but also only turns on when a kid goes down there (rarely).

    Last night, the boy took a long shower and my wife set the tub to fill after walking our dog in 20F weather. Needless to say she was NOT happy when she put her foot into ice cold water.

    Interestingly, the tank replenished in 20-25 minutes I think. That's when boiler turned off.
     
  18. Dana

    Dana In the trades

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    Are the tubs extra-large 80 gallon soaker tubs of the type phog refers to in response #15, or are they just standard normal sized tubs taking 35-40 gallons to fill? (I kind of doubt they're soaker tubs, which are hard to fill under any circumstances at MA type incoming water temps from a 50 gallon indirect maintained at 130-140F.)

    Either way, with the water heater zoned as primary the boiler has capacity to spare for the endless shower, and it shouldn't be taking 20 minute to recover if it's being pumped properly and the boiler output temp on hot water calls is at least 20F hotter than the storage temp. A 50 gallon tank has about 417lbs of water in it, and at 100,000 BTU/hr (~1667 BTU/minute) the temperature should be rising 1667/417= ~ 4F per minute. In 20 minutes that would be an 80F rise.

    If the tank's setpoint temp is 145F that means the average temp in the tank needed to have dropped to 65F- I doubt the kid was showering at that temp, and the boiler should have been cycling on/off satisfying he aquastat during the endless shower.

    Have you bucket-tested the shower flow with a stopwatch to measure it's actual gpm?

    A 55 foot zone can only emit about half that boiler's output at minimum fire at condensing temperatures. Even with both 55 foot zones calling for heat it barely emits more than the minimum fire output at condensing temps. The original designer probably assumed a 110' x 500 BTU/hr = 55,000 BTU/hr design load, but your reality is probably closer to half that (especially after the insulation and air sealing upgrades. No matter what, even at 180F output and both zones calling for heat there is at least as much spare capacity for the wter heater as a standard 50 gallon standalone. You should EASILY be able to make the domestic hot water work if the water heater is the priority zone, unless you're trying to fill a monster spa tub from a 50 gallon tank.

    How bad is the cycling when just one zone is calling for heat?
     
  19. Dana

    Dana In the trades

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    The fact that it's taking 20 minutes to satisfy the water heater may be an indication that it's not being given priority. If the water heater isn't the priority zone, it should be. The KBN106 has about 3x the output of a typical standalone, and the recovery from a too-tepid-to shower 90F average tank temp to a bathtub-hot 110F would take less than 10 minutes.
     
  20. phog

    phog Member

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    Rochester NY
    Hi eoren1, I agree with Dana that something fishy is going on here. You should have faster recovery than that.

    I took a quick look at your manual; you should be able to see via the boiler's front display which zone is active, along with the burner's modulation level. When the priority zone (Domestic Hot Water) is calling for the boiler, you should see "BLR: DHW - xx%" on the display. The rest of the time, you should see "BLR: SH - xx%" (Space Heating) or "BLR: Standby" (off). The xx% is the burner modulation level and will be a number between 0-100%.

    Confirm that over the course of the day, you see both "SH" and "DHW" zones appear as active on the display at the appropriate times. If you only ever see the "SH" zone on the display even when the hot water tank is calling for boiler heat, your system was not installed correctly. (Or if you only ever see "DHW" zone even when the water tank is not drawing -- though this is probably unlikely). Fixing this zoning would cause a world of improvement.

    One other thing to check. Note the burner modulation levels you see. The manual says that if the flue gas temperature sensor is broken, the boiler will not module the burner above 50%. So make sure you see numbers above 50% at least sometimes. If you don't, your flue gas sensor is bad & repairing will double your boiler's max output.
     
  21. eoren1

    eoren1 New Member

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    Location:
    Massachusetts
    Hi Phog,

    I think the boiler is working correctly.

    Tonight, my daughter took a 5 minute shower. Wasn't downstairs to check while she was showering but ran down soon as she finished and boiler was on STANDBY.

    Then it was my son's turn. Within a few minutes, the Knight went to Pre-Purge with system temp 97F and tank 122F (outside 24F). The icon for hot water came on and DHW Pump signaled on (Boiler and System pumps off). Then Ignition with inlet temp 66F; outlet temp 114F; flue temp 108F.

    Then (took photos as values increased quickly - seconds):
    % ---- Inlet ----- Outlet ----- Flue
    43% 60F. 97F 105F
    60%. 90F 84F 103F
    70% 96F 88F 104F
    68% 84F 113F 108F
    76% 77F 117F 108F
    100% 74F 112F 110F

    At 100%, Flame current 12.9uA; Fan 5200rpm
    DHW Pump On; Boiler and System pumps off
    Rate output 9.9V
    System 96F; Tank 82F (130), Outdoor 23F

    Boy finished shower 8 minutes later (9:33pm)
    100%. Inlet 132F. Outlet 170F. Flue 198F
    System 92F; Tank 81F (130); Outdoor 23F

    Just checked at 9:40pm
    83%. Inlet 150F. Outlet 182F. Flue 200F
    System 89F; Tank 108F (130); Outdoor 23F
     
    Last edited: Jan 15, 2019 at 6:54 PM
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