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New Boiler plus Indirect HW

GBA Editor | Posted in Energy Efficiency and Durability on

I’ve decided to replace the oversized boiler and WH on my house. I am considering a Prestige boiler with a Triangle Tube Indirect WH, like you recommended Robert. Prestige makes a 60,000 BTU boiler which modulates from 16 to 60,000 depending on the weather…..and a 110 which modulates from 25 to 97,000 BTUs in an LP system. Manual J came out with a 46, 000 BTU need and Micropas a 52,000 BTU need so I am inclined to buy the Prestige 60. The salespeople are of course recommending the 110 in case a big storm hits and……it is a smart system where it modulates according to the weather so why risk buying a smaller unit, as the story goes. They always just want to know the square footage of the house then they make a recommendation. I don’t get it. We could have single pane glass with no insulation and air leaks all over the place…..or triple pane glass with closed cell foam and minimal air leakage. Estimaters don’t even ask about the quality of construction, etc. Prices between the two boilers are not significant, I don’t think.

I will be adding heat transfer plates and rigid foam to the bottom of the joist bays, like you suggested Martin (unless someone can point out good energy saving reasons for insetting the foam in each joist bay) so the system should respond much more quickly.

We live in the foothills of the Sierra Nevada mountains near Lake Tahoe…..5600 heating days.

Any other recommendations or warnings?

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Replies

  1. Riversong | | #1

    I would go with the 110 if you're using it for domestic hot water in addition to space heating.

    The DOE net output for the Solo 60 on LP is 54,000 BTU/HR and the 110 on LP is 87,000.

  2. user-723121 | | #2

    I agree with Robert, go with the 110, if you set back your thermostat at night the smaller unit will not handle the pick-up load. I sized our two-stage funace at twice the design temperature and could not be happier with the performance.

  3. Ed Welch | | #3

    110, huh, did not expect to hear that.....but if it does modulate, maybe it is not a big deal...thanks for the input.

  4. Ed Welch | | #4

    Or maybe I stick with the 90,000 Lennox boiler that does not modulate.....adding the Hot Water may increase the need enough....not sure how much the modulating units actually save in energy use...hmmm

  5. Riversong | | #5

    A modulating boiler is more efficient for several reasons:

    By reducing burn rate and water temperature when the outdoor temperature is below the design minimum, stack losses are lower, heat exchange efficiency is higher because of greater delta-T, short-cycling, distribution losses, and room temperature overshoot are all reduced.

    The latter increases comfort, as does the increased circulation run times. While the radiant temperature of the floor will be reduced, it will be more consistent.

  6. Ed Welch | | #6

    Thanks Robert.

    I'm still trying to decide between the PS 60 and the 110.....seems counter intuitive to go from an oversized 90,000 BTU boiler to a 110....but if it modulates correctly, it should be much better...the outdoor reset controller being the key, I think.....I was told that the 60 and the 110 would almost operate the same except for when massive storms hit and in the hot water recovery which is better for the 110....not that I really want it for that component....maybe I can turn down the factory set temperature for the domestic hot water priority....and if I can program the thermostat for lower nighttime temperatures, maybe I will be happy with a faster recovery.

  7. RichK | | #7

    Ed isn't the boiler you're considering replacing brand new? If the boiler is new you should concentrate on the building shell upgrades not on replacing the equipment. Add the transfer plates, wrap the underside of the floor with thick rigid foam and insulate and air seal the rim joist. You can find better opportunities for your investment then on replacing new working equipment.

  8. Ed Welch | | #8

    Rick....good advise, I understand your point and I often tell people the same thing....but the existing boiler is not really compatible with an indirect water heater because it does not have domestic HW priority......and I think the fixed oversized unit wastes a tremendous amount of energy because it does not modulate....don't worry, I am planning to do all the building shell upgrades

    Thanks for the good home performance advice.

  9. Ed Welch | | #9

    Robert,

    According to my plumber, adding the domestic hot water will not add to the load for the boiler because it does not do both at the same time....in other words, it has a domestic hot water priority and will not be heating the floor for the WH recovery time. So, the 60 would likely be enough for my house. But it appears that the 60 costs the same or even more than the 110 because of a built in pump in the 110. Anyway, I am likely to install the 110, giving the capacity for quicker recovery time and hopefully not wasting energy because of the modulation.

  10. Riversong | | #10

    I understand that the Prestige has an over-ride of the heating side when the tank calls for hot water (I recently speced and installed a 110 in a super-insulated house), but that means it's not available for heating while the hot water is recovering. So, depending on how much hot water your household uses, the 110 will not only offer quicker recovery but also quicker return to its space heating mode. That might be an issue only when using a lot of water or on the coldest nights. But given the lack of price difference and the included low-consumption circulator, it doesn't make sense to buy the smaller unit.

  11. RichK | | #11

    Ed it seems like you already have your mind made up but I'll try to be the last voice of reason. You can add an outdoor reset controller to your boiler with priority DHW making your existing system more efficient.

  12. Ed Welch | | #12

    Thanks Rick for your gentle voice of reason. I do hear you. Another local performance contractor has also advised me to wait before replacing the boiler.....plus the Prestige boiler is very expensive, approximately $3000 plus installation. So I am stepping back, planning on attaching an indirect water heater to the existing boiler, doing all the thermal improvements, etc.....then possibly replacing the boiler in the future. It would interesting to see the energy improvements without replacing the boiler first....then maybe view improvements by replacing the existing oversized unit with a modulating boiler.

    I did not know that you could add an outdoor reset controller to an existing boiler or domestic hot water priority. Can you tell me more or link me to more information? My boiler is a Lennox signature series, built in 2004. Although, I am not sure how an outdoor reset controller would help with a non-modulating unit? And I suspect, the Lennox boiler will simultaneously heat the floor and the domestic hot water at the same time......I'll check the owner's manual, consult technicians, etc and get back to you.

  13. RichK | | #13

    I don't know that you should worry to much about the brand but more on selecting a contractor that has experience with that product. Taco, Honeywell and many others make boiler controls I believe the outdoor reset hooked to your cast iron boiler would help more then if it were hooked to a mod/con boiler. Using this system on your boiler will allow the system to use the mass of the boiler more efficiently and at a lower circulating temp.

    If you have the time please post back to let us all know how the incremental improvements worked out.

  14. Garth Sproule | | #14

    Ed
    Lots of good info in the downloads over at
    http://www.tekmarcontrols.com/literature/e.html

  15. adkjac upstateny | | #15

    I have just worked on an installation that you are asking about. The home has the 60 size Prestige with an indirect tank. All is working well... one problem at start up solved by sizing the propane piping oversize to 1". For some reason this unit is sensitive to not starting with smaller feed lines on the odd occasion according to the rep that helped out.
    aj

    Someone above mentioned night time set back recovery issues... from what I have read and noticed with radiant heating... it's not recommended. My idea that I am working on is a way to set back bedrooms only in future installs. And bathrooms just the opposite... they need to be well heated and ready to enter when the alarm goes off.
    aj

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