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Munchkin 140M, fighting the typical F09. NG fueled



  • TT_Vert
    TT_Vert Member Posts: 57
    edited March 2021

    Any opinions? I am going to see about getting someone out to replace this boiler. The first company I called still hasn't called me back which is getting me thinking about installing a unit myself. Aside from not having a pipe threader that big (they're cheap) I have every tool and bit of knowledge I'd need to do it. Full disclosure again, i've never done it but I have replaced hot water heaters and replumbed as well as various gas and water pipe plumbing. Not to mention a decent amount of experience in HV and LV wiring. I would be curious to know your opinions on sizing. I've done the heat loss calculations to the best of my ability but I am getting a bunch of conflicting info on this. Some are adamant you can size BELOW your heat loss calcs when you aren't using them for DHW (I am not). Some say give yourself 10% overhead (Slant fin app actually lists usings w/ 10% overhead), one person on this forum said 20%. The theories have ranged from "let the thing do its job" when undersizing to it never being able to be in it's efficiency window for long (Or at all) when it's too big to "you can never fully estimate the hot water you'll need". Our home depot has rheem which appears to be the Ruud brand at menards. They have one that is rated 18K-100K BTU (heating mode) and even appears to have an integrated 9GPM circulation pump as well as auto feeder/pressure regulator. I would have to replumb the entire system of course to remove my auto feeder, back flow valve and circ pump but I could make it a cleaner install w/ this wall mounted unit. Funny enough the thing that is annoying me is that most of them have the exhaust on the left and the intake on the right. My munchkin is backwards to that so I'd have to cross the two 3" PVC pipes and then bring them back flush against the wall which is going to kill my OCD. I'd almost want to replumb the entire exhaust and rotate that concentric exhaust stack 180 deg. so I didn't have to cross the two pipes over each other. That would of course cause me some drywall work in the ceiling of the room the burner is in as they have it clocked in a way where the exhaust is currently flush against the wall and the intake is a good 3" off the wall based on the way they exit the unit. They did a good job on install, it's just the way the pipes exit that dictated this. I included a pic but ideally (To tidy up the plumbing and condense it a bit) i'd love to mount a wall mounted unit above the manifolds but that'd require more elbows for the intake/exhaust or moving it in roof (Not an option I'll consider) The fact they have the water side already plumbed makes me just want to go w/ another floor mounted unit and call it good. I'm still stuck w/ having to cross the intake/exhaust w/ most units but it would only require minor replumbing on the water and gas sides.

    Thanks much,

  • Is there an attic above?

    Some boiler manufacturers don't want you to use PVC for venting.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • TT_Vert
    TT_Vert Member Posts: 57

    Is there an attic above?

    Some boiler manufacturers don't want you to use PVC for venting.

    Nope exits right out. Manuf does say PVC is ok.
  • tim smith
    tim smith Member Posts: 2,619
    What did you end up installing?