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Help with choosing boiler for small load

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tbrooks
tbrooks Member Posts: 100
in Radiant Heating
Ok guys I have definitely decided on an lp boiler. I think that is a must have for me. Now my total heat load is about 26mbtus, my largest zone only needs about 8mbtu, and my smallest is 512btu. So I have been looking for the lowest mod boilers I can find. I'm not real sure if that is the right decision, as I'm positive I will need a buffer tank no matter what. And I think because of such low demand that I should use a separate heat source for dhw.

After pouring over lots of boiler specs, it seems my best 2 options are the htp utf 80 with 10:1 turndown, or the Lochinvar kh o55. Both will modulate down to around 8mbtus. I'm leaning more towards the htp after looking at costs and I've read the Lochinvar can be complex to set up. Heck I'm not even sure I can get the Lochinvar anymore, seems half the boilers I look up have been discontinued. It is hard to find a boiler searching on the web, so any input you guys have would be much appreciated.

Comments

  • hot_rod
    hot_rod Member Posts: 22,158
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    Either would be a fine choice. I have helped with a few Lochinvar installs recently, the control is very simple to use, the color changing screen is a fast visual for keep an eye on the system. ConXus is a nice feature if you want remote access. The ramp delay and other features on the control help dial it in to system needs.

    Support for the product and parts availability should also be part of your decision.

    Any way to move that 512BTU/hr load to one of the other zones?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • NY_Rob
    NY_Rob Member Posts: 1,370
    edited February 2018
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    First question....
    Are you installing it yourself or will a contractor be installing it?

    I believe the current small wall mount Lochinvar is the WHN056: https://www.supplyhouse.com/Lochinvar-WHN056-44000-BTU-Output-Knight-High-Efficiency-Boiler-w-Fire-Tube-Heat-Exchanger-Wall-Mount

    The Loc is almost 2x the cost of the UFT-80W, but it's got a much more robust operating system and many more programming choices that can make it fit/run with a wider array of emitters. When I see all the choices you have with the Loc, it made me second guess my decision to go with the HTP. If you have a simple system with similar radiation types, the HTP would probably be fine.
    You'll have to download the install manual for both and compare the two to see if the Loc has something that the HTP doesn't then make your decision.

    When computing your radiation BTU output, use 130F AWT (140F SWT) because that's a sweet spot for mod-cons where you will be condensing.
    Unless you can combine that 512BTU zone with another zone to bring the load up to 8K BTU's it will drive the boiler crazy. Adding a buffer tank will address that, but it's big $$ extra vs. combining that small zone with another zone if possible.

    Both are fire-tube HX, so that's good.
    Did you compare warranty's?
    Loch is 15yrs HX, 5yrs parts.
    HTP is 10yrs HX, 5yrs parts.

    I don't think you could go wrong with either one... just be sure you can source spare parts for whichever you chose before you dive in. Supply houses don't (usually) stock parts for mod-cons and unlike traditional cast iron boilers- mod-con parts are not generic. You can't find parts for them at HD or Lowes. When a simple $5 flame sensor can put out out of commission- you need to be able to get that part quickly.



  • pecmsg
    pecmsg Member Posts: 4,861
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    Maybe I missed it but what temperature are your emitters or radiators rated at?

    Will they support the lower output temperature of the new boiler!
  • ced48
    ced48 Member Posts: 469
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    I'm using the older WH55 Lochinvar to heat a smaller house with a true design demand of only 15k. The boiler almost never runs over 20 percent, after reaching set point. I heat with water from 110 to 125 degrees, lots of baseboard. House is comfortable and cheap to heat. No short cycling. Also, because the system runs at only 20 percent, it is super quiet.
  • tbrooks
    tbrooks Member Posts: 100
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    Sorry guys, I should have gave you some more info. I'm doing the total install myself. It's basically a radiant floor retrofit, stick framed floor, pipe above subfloor with plywood sleepers and aluminum plates. I had a pro do my heat loss and pipe design, I requested alot of zones, partially because I have split custody of my kids, so they are only with me half the winter. I insulated the majority of my interior walls because of this.

    The 512 zone is the master bath. It's the only zone without an exterior wall. I might be able to just combine it with the bedroom circuit, but I don't know what affect it will have. I feel that aggressive zoning is necessary with my situation, and plus the old lady is very sensitive to temps, hot or cold. I'll try and put up a couple pics from the design.

    @ced48 good to hear from someone with a small system. I know our emmiters are different, but wat kind of zoning do you have?



  • tbrooks
    tbrooks Member Posts: 100
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    Oh and I'm not actually doing a lightweight over pour like the design paper says. I assume he just had that on there to make my plan work with his software.
  • ced48
    ced48 Member Posts: 469
    edited February 2018
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    1 zone, direct, no prim/sec
  • NY_Rob
    NY_Rob Member Posts: 1,370
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    Before you make your boiler brand decision... call Lochinvar and see if they will warranty "non-contractor self installs".
    HTP has no warranty problems with the above FWIW.

    Also, some manufacturers won't talk to/offer tech support to non-trade callers. HTP support will talk to homeowner/installer callers, don't know about Lochinvar.
  • DZoro
    DZoro Member Posts: 1,048
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    @NY_Rob Good idea no matter which boiler. Our company just made the switch from TT to Lochinvar about 6 months ago. Very impressed with Lochinvar, and their support. Price point of parts is good, set up is very easy and give many options to customize your situation.
    Good luck, suggest a buffer tank with your small zones. Will help the efficiency in the shoulder months of the heating season.
    Again either way check out your support team.
  • ced48
    ced48 Member Posts: 469
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    Yes to both -
  • Gordy
    Gordy Member Posts: 9,546
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    Price point HTP UFT. Features lochinvar Khn.
    NY_Rob
  • Gordy
    Gordy Member Posts: 9,546
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    To the OP if you are not doing light weight (gypcrete) overpour what is your radiant panel detail? There is a difference in water temps.
  • tbrooks
    tbrooks Member Posts: 100
    edited February 2018
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    > @tbrooks said:
    > Sorry guys, I should have gave you some more info. I'm doing the total install myself. It's basically a radiant floor retrofit, stick framed floor, pipe above subfloor with plywood sleepers and aluminum plates.

    Kitchen and baths will have tile with ditra underlayment. Rest of the house will have engineered hardwood 1/2" thick, felt underlayment. Although I don't know if the felt is a good idea with the heat...

    Should I mention this concern to my designer? May they have compensated for this elsewhere?

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