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Thread: Which Tankless To Install

  1. #16
    Retired Defense Industry Engineer jadnashua's Avatar
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    The metal flue can obviously handle higher temperatures in the exhaust. Doesn't mean that it may not be condensing at least some of the time, though. Metal is (from what I read) usually necessary when the average efficiency is below 90%.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  2. #17
    In the trades Dana's Avatar
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    Quote Originally Posted by dtherrien View Post
    Dana...Where can i find more info on the mini-splits that you are talking about?
    Yes i am in central Ma. and electric and propane are high. I am paying about $4.50 gallon for propane....company says i am not using enough to get the heat rate. I am thinking about getting my own tank and get delivery from who ever has the best price.What is that setup in the picture above? I understand the drain water part...but what brand is that heater and does it heat both the domestic hot water and water for home heating?
    There are literally dozens of mini-split contractors in central MA, some more competent than others. It's been my own m.o. to calculate the heating load myself, narrow down to 2-3 models that fill the bill, then solicit bids. I'm also pretty picky about telling them where/how to install the compressors. Since the tools & skill sets are mostly air-conditioning (they are heat pumps after all), many contractors don't consider aspects like snow-depth, snow drift or ice-dam/roof-avalanche fall very carefully (or at all), leaving the homeowners to be out there dig up the compressors after every storm (or worse.) Mitsubishi has the lions share of total numbers of contractors & support in our area, followed by Fujitsu, with the rest "in the statisitical noise". Contractors that have a lot of experience with Mitsubishi are Chaves in Hudson, Advanced Energy Conceptsin Fitchburg, and Meacham in Charleton, all of whom are on the "quality" end of installers, but it's still best to detail where/how to mount the outdoor unit.

    I'm not sure who the better Fujitsu installers are in the neighborhood, but you can find some here. Daikin makes some of the better equipment (and are one of the bigger operators worldwide), but they don't have very many certified installers in central MA. If you stick with those three you'd be in pretty good shape from an equipment performance & reliability point of view.

    In our climate it's not absolutely necessary to go with the "cold weather" series, units, but there are fewer maintenance/performance issues to worry about if you do. In the Mitsubishi lineup those would be the "Hyper Heating" sometimes called "H2i" series (MUZ- FExxNA). In Fujitsu it would Halcyon XLT-H series (AOU-xxRLS2-H). A typical "pretty-good" mini-split like those would have about 15,000 BTU/hr output at +5F per "ton" of rated cooling. (So a 12,000 BTU/hr = 1-ton unit is really 15,000 BTU/hr from a space heating perspective, in our climate.)

    The layout of your house makes a difference in how many heads you'd need, and what size. Make a spreadsheet (Excel, etc) for calculating an I=B=R method heat load calculation on a room-by-room basis. You'll have to come up with U-factors (heat loss per square foot per degree) for your wall construction, windows, doors, attic, foundation (above grade only), etc. and the appropriate indoor/outdoor design temps. (Use the 99% outdoor design temp for your area if listed, or interpolate for the nearby listed locations. In Worcester the 99% design temp is +5F, and yes, it drops to -5F every few years, but it doesn't dwell at those temps long enough to really matter from a heating system point of view.) The basic formula for calculating the heat load is:

    U-factor x area x temperature difference. So for each room you would have separate U-factors and areas for wall, window, ceiling to be calculated separately, then summed.

    With a room-by-room heat load and a whole-house load I can steer you toward potential solutions.

    Open common areas and adjacent rooms that open up directly onto it are usually candidates for running as one "zone", with a single head. A big doored-off room with lots of windows down at the end of the hall not so much. If a room doesn't have a heat load of at least 6-7000BTU/hr it's not a candidate for having it's own head, but there are "mini-duct" cassettes where you can split output between two nearby rooms with very short duct runs. Like space heaters and wood-stoves it's point-source heating, but it's not bad. Since they modulate rather than cycle on/off you get very stable room temps, and most of the time they're quieter than your refrigerator.

    Since you have a heating fuel history on the place you can get a pretty good handle on the whole-house load by using propane-use against heating degree days. To do that we would need a zip code (to find a degreedays.net weatherstation nearest you), the # of gallons of a late-winter fill-up and the exact dates between that fill-up and the prior one, and the nameplate efficiency on your Rinnai heaters.

    The picture of the drainwater heat exchanger (a 4" x 48" PowerPipe) is clipped from a Natural Resources Canada website. It looks like a Rinnai RL75i or similar, probably not set up for space heating, only hot water (since it would violate the Rinnai warranty to use it as a hydronic boiler.)

  3. #18
    DIY Senior Member guy48065's Avatar
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    hmmm...is combustion air temperature factored into efficiency? Concentric is pricey--if it won't pay for itself I don't see any reason to choose it. Still wonder why Rinnai does...

    I may end up with 40 feet of vent so cost is a factor. The price difference between concentric & PVC can cover the extra cost of a condensing unit.

    Edit--oops I didn't notice we're on page 2. My reply is to post 15.
    Last edited by guy48065; 10-09-2013 at 08:03 AM.
    Romeo and Atlanta, MI

  4. #19
    Retired Defense Industry Engineer jadnashua's Avatar
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    The more heat the unit extracts from the burner (the less goes out the flue), the more efficient it is...the more efficient units can use plastic pipes solely because they extract more heat and the flue temps are lower.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #20
    Licensed Building Contractor dtherrien's Avatar
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    I will have to do some more research on the mini-split systems....seems more complicated than i anticipated.
    I live a couple of towns away from Charleton so might contact Meacham. I will also ask two other plumbing/heating subs that i use.
    One thing about my house is....there is no type of central heating system. I bought this house in 1996 and it had only a propane fired heater upstairs and downstairs. I replaced them with the Rinnia heaters. I dont know if that works for me or against me...but have the option to do almost anything. Kinda looking for something that i would be able to do myself.

  6. #21
    In the trades Dana's Avatar
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    The fact that you've been heating with a couple of Rinnai space heaters means it can probably be heated reasonably with just two mini-splits. The output of the mini-split heads probably doesn't need to be as big as the output of the Rinnai heaters though. You could just install a couple with the same output of your space heaters, but if oversized they would be more expensive, and would cycle on/off rather than modulate, running at slightly lower efficiency, more noise, and greater swings in room temps.

    It's possible to do 90% of a mini-split installation as a DIY, then have a qualified tech do the final pump-down, refrigerant fill, and system testing, keeping the whole thing under warranty. The hardware itself isn't outrageously expensive. A MSZ-FE18NA with brackets for mounting the exterior unit on the wall (above the snow line, protected from roof avalanches by the rake or eaves of the roof) plus refrigerant lines adds up to and puts out about 22,000BTU/hr @ +5F. The same unit installed by a high-end installer who backs it up runs about $4400. The 1-ton version runs about $2K with the associated hardware, and puts out about 15,000 BTU/hr @ +5F. The 3/4 ton would be under $2K, and puts out better than 10,000BTU/hr @ +5F. A 2-head single compressor 2-ton would run about $3500 for the all-in hardware costs.

    It's worth reading up on how to install them before going the DIY route, but if you have it all set up reasonably it would probably cost less than $500 for the tech time to pump down charge & test two separate systems.
    Last edited by Terry; 12-15-2013 at 02:49 PM.

  7. #22
    DIY Junior Member jocko91's Avatar
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    I need some quick help. I am 91 and am giving up my hot tub because I have difficulty getting out of it. So I am replacing our MBR jacuzzi tub with a walk in tub 32" high. But I want to be able to fill the tub quickly (60 gal) and with 102 degree water.

    So I plan to get an electric tankless heater just for the tub. The questions are:
    1) which one?
    2) hook it to the hot water line or "regular" line?
    3) if hot water line, mount upstairs next to water heater (50 gal gas) or downstairs next to tub?
    4) I plan to use the existing hot tub 220v for the heater and tub.

    The tub arrives next Wed so I need to make a decision soon so I can be ready to install it when it arrives. Thanks

  8. #23
    DIY Senior Member lifespeed's Avatar
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    You need to use gas if you want tankless, or get a larger tank. Electric can't do what you want.
    Lifespeed

  9. #24
    DIY Junior Member jocko91's Avatar
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    Could you please explain that to me?

  10. #25
    DIY Senior Member kcodyjr's Avatar
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    Well, actually yes an electric tankless can do it, but it would be a big unit, and would need two or three 8ga or 6ga 240V circuits.

    If you went that route, you'd want it right there next to the tub if possible.

    Unless the tub is being used multiple times per day, I'd go with a larger tank, and/or run the tank hotter with a tempering valve.

    Edit: In order to determine exactly how big a unit, we'd need to know the flow rate of filling a tub (more than a shower) and the cold water temperature at the dead of winter, to determine how much energy needs to be dumped into the water and how fast. Off the cuff, I think you might need the big one, a 29 or 36 kW 3-element unit. That means a 200 or 300 amp electric service into the home. Check out Stiebel Eltron, they seem to be the go-to brand and have sizing charts.
    Last edited by kcodyjr; 11-27-2013 at 03:41 PM.

  11. #26
    DIY Junior Member jocko91's Avatar
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    Tub holds 60 gal but wouldn't need that much because of body displacement. So what would you figure I would displace at 6' 2" and 220 pounds? Maybe 15 or so? Then I wouldn't need but 45 gal? Would that do it? My water heater is less than a year old so I hate to replace it. But if I did, would it get temp up to 102?

  12. #27
    DIY Senior Member lifespeed's Avatar
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    Quote Originally Posted by jocko91 View Post
    Could you please explain that to me?
    The electric power required to heat water at a rate that would fill a tub quickly is fantastic, probably more than your circuit panel can provide. Despite silly comments to the contrary claiming it is theoretically possible, I assume you live in the practical world with the rest of us. So forget electric tankless for your application.

    The most practical thing to do is either gas tankless (this requires gas and vent plumbing) or increase the size and/or temperature of your tank heater and use a tempering valve to increase capacity via higher temperature.
    Lifespeed

  13. #28
    DIY Senior Member kcodyjr's Avatar
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    Quote Originally Posted by lifespeed View Post
    silly comments to the contrary claiming it is theoretically possible
    What's silly about it? Presumably you also saw me recommend against it. Showing exactly why it's impractical is a nice, straightforward, honest, nonconfrontational way to talk someone out of doing something silly, and generally more effective than just trying to present oneself as the Voice of Unquestionable Wisdom.

    Hence, I directed him to the wattage charts.

    Hope you're having a pleasant evening.

  14. #29
    DIY Senior Member kcodyjr's Avatar
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    Quote Originally Posted by Reach4 View Post
    I would think that concentric steel would have the advantage of pre-heating the incoming air from the exhaust heat. It would also leave one hole in the house instead of two.
    The concentric vents do preheat the incoming air, and precool the exhaust, but not nearly to the degree that the condensing units do internally.

  15. #30
    DIY Junior Member jocko91's Avatar
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    OK, I checked out Stieble. http://www.e-tankless.com/stiebel-el...ter-heater.php

    My data: 1) winter ground water temp here in Northern Va is 55-57; 2) desired heater output temp 102; 3) fill rate 4+ gpm. (BTW, I considered getting a hot tub heater to replace the inline new tub heat exchanger but it would void the warranty.)

    Maximum Flow Rate in Gallons Per Minute at 105F Output temp
    Incoming Water Temp: Flow Rate (GPM)
    40F 3.0 GPM
    45F 3.3 GPM
    50F 3.6 GPM
    55F 3.9 GPM
    60F 4.4 GPM
    65F 4.9 GPM
    70F 5.6 GPM
    75F 6.5 GPM
    * this chart is based on 240v input. Please review the Stiebel Eltron Tempra Brochure for temp rise data at 208v input.

    If I read this correctly, I get output of 3.9 gpm at 105 degrees so at 102 flow would exceed 4.0. And if we pulled the water from the heater at 100(?) degrees, it would probably get to 8 or 9 gpm. And the $800 is less than a new gas water heater would cost

    I feel bad for having asked for expert advice, got it and still want to press on with electric tankless, but that is really what I want to do unless it is just downright dumb. So please tell me like it is -- keep me straight. Please!

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