Peerless Pinnacle PI-80 for Gas conversion with radiant

Discussion in 'Boiler Forum' started by Jim36, Dec 6, 2013.

  1. Jim36

    Jim36 New Member

    Messages:
    1
    Location:
    01760
    Hi all. Firts time posting, thanks for having me. I'm getting ready to do a remodel on my home in metrowest Boston. It will be approx 2300 sq ft (1300 1st Fl, 1000 2nd FL) when I'm done. The rear 1/2 of the house will be new construction and the front 1/2 is 1890 built. It has been retrofitted with icynene, however, so that's something I guess. We will be replacing all the windows with energy efficient double hungs, although there's like 33 of them. I plan to change from oil to gas and I'm considering doing radiant for the whole house. With a preliminary heat load calculation (I think I found it on the Crown website), and some basic draft plans I came up with approx 60K BTU. I was hoping to use a Peerless Pinnacle PI-80 with a Crown INdirect DHW because my father removed the whole set-up from his condo and it's VERY affordable. Any thoughts on this particular unit and it's applicability to my needs? Does anyone know if this particular boiler is any good? I haven't found much info on it, other than it takes cheaper Munchkin replacement parts. Any recommendations as to alternatives are welcome. I'm hoping to do much of the tubing installation myself, but am also looking for reputable contractors in my are, if you know of any. Thanks,
  2. Dana

    Dana In the trades

    Messages:
    2,933
    Location:
    01609
    A heat load of 60K seems way high for a 2300' two story with code min U0.30 replacement windows and ~R13 open cell foam in the walls. Your 99% outside design temp in metro-west is going to be in the high single-digits F (at 1000' of altitude in Worcester it's +5F), so you're looking at a delta-T on the order of 60F at design temp.

    Assuming you have about 2000' of floor suitable for radiant, a 60K load means 30 BTU/ft, which means you'd need a more-expensive type radiant solution to get there. A decently insulated house that size with code-min windows would usually come in at about 15 BTU/ft of conditioned space at a 60F delta-T. If you have an oil-use history on it (or a K-factor on a late winter fill-up, if you do regular fill ups) we can sanity check the 60K heat load number. Are you using 1500 gallons a year, or something like 750-800 gallons?

    A totally crude I=B=R type heat load calc on a place approximately like yours, a 30 x 40' x 25' tall 2 story goes something like this:

    A typical double hung is 10-11 square feet. MA is currently under IRC 2009, some towns have stricter minimums, but a code max window under IRC 2009 for MA would be U0.35. So, assuming 11' per window you have 33 x 11= 363' of window. At a U-factor of 0.35 and a delta-T of 60F your window losses are:

    363' x 0.35 x 60F= 11,435 BTU/hr

    Lets assume you have a front and back door 2" solid wood, which has a U-factor of about 0.5. A couple if doors adds up to about 45 square feet. Door losses:

    45' x 0.5 x 60F= 1,350 BTU/hr

    Your gross wall area is the perimeter times height. Perimeter is (30x2) + (40x2)= 140' times 25' is 3500'. Less window and door area leaves ~3100'. A 2x4 balloon framed 1890s house with Icynene or cellulose cavity fill has a U-factor of about 0.1. Wall losses are then:


    3100 x 0.1 x 60F= 18,600 BTU/hr.

    Assuming you have enough room in the attic to hit the R38 min, that's a U-factor of about 0.03 (assuming the joist tops aren't covered.) With a 1200' footprint the roof losses are:

    1200' x 0.03 x 60F= 2160 BTU/hr

    Add it all up and before basement losses and infiltration you're at about 33.5K, nowhere near 60K.

    Assuming NO insulation in the basement and a couple of feet of above-grade exposure you could add maybe 15K to that, and if you have the leakiest house in metro-west (not likely, with open cell foam insulation and new tight replacement windows) another 10-15K to hit the 60K numbers, but real houses that size typically measure out via fuel use against heating degree days under 50K with no foundation insulation, and under 35K with the foundation insulated.

    If you can get the whole house load down to 30K (or if it's already there) you'd be looking at something very amenable to retrofitting radiant floors at a more reasonable cost.

    For new construction with radiant floor heating in mind it's best to keep the window/floor ratio on the conservative side. A typical whole house window/floor ratio for US new construction is about 14-15%, shoot for 11-12%. in your design, since the windows will be the lossiest square feet of the wall. To that end, look for something under U0.28, not a code-max U0.35 (or IRC 2012 code min U0.32 ). The difference between a U0.25 window and a U0.35 window is something that you can FEEL standing next to it with your eyes closed on a cold day.

    And shoot for something north of R20 for a whole-wall R (code min 2x6 R20 comes in at ~R14 after factoring in the thermal bridging of the framing.) A higher-R wall makes for both a lower heat load, and higher comfort, since the interior side wall temp is much higher. A 2x4 wall with open cell foam cavity fill and 2" of rigid polyiso between the sheathing and siding comes in at ~R22 whole-wall, at the same wall thickness of a 2x6 code-min wall, and has 35% less heat loss.

    The Peerless Pinnacle series is pretty good mod-con, it's well worth re-commissioning the PI-80. If you don't micro-zone the hell out of the place it should do just fine. Online reviews of mod-cons (including the Pinnacle) trend toward the negative, but if you dig down into it it's mostly an installer-error/system-design problem. Low mass boiler installatoins aren't very DIY friendly either, and they have many sensitivities to the system design that cast iron boilers don't have. Just sayin'- don't be put off if you see bad reviews in any online research, but DO seek out competence on the system design and installation. The minimum fire output on the thing is about 18,000BTU/hr which is probably about half your true heat load, which means if set up correctly it should modulate with very long efficient low-temp burn cycles for most of the winter, rather than cycling on/off constantly at a cost in efficiency, comfort and boiler life.
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