Is high efficiency boiler worth extra $4,000?

Discussion in 'HVAC Heating & Cooling' started by davidwie, Jan 23, 2014.

  1. davidwie

    davidwie New Member

    Messages:
    11
    Friend building a new house (around 6,000 sqft). He is deciding between standard 85% efficiency boiler vs. the 95% high efficiency. Upcharge is about $4,000.

    Doing radiant in some of the house and then whole house is hydrocoil. Contract calls for 2 boilers, 180,000 BTUs each. That's the 85% ones. The 95% would be a weil-mclain ultra 3, 95% efficiency, one boiler (assuming the same 360,000 BTUs).

    He'll have approx 9-10 zones, including the 120-gallon storage tank.

    Any advice?

    Thanks.
  2. Tom Sawyer

    Tom Sawyer In the Trades

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    Maine
    10% difference times the amount and cost of the fuel uses. Do the math.

    Lets say the cost of operating the 85% boiler for a year is 800 bucks

    So the 95% efficient boiler is going to cost 80 bucks a year less to operate

    divide that 4 grand up charge by 80 and you get.......a 50 year payback ratio.

    Of course the boiler will either crap out or be yesterdays news or you will be dead by then.

    The big problem here is that even though 6000 sq/ft is a big assed house, unless it is 95% glass and uninsulated it ain't going to need anywhere near 360 thousand BTU/HR to heat it. Who did the heat loss?
  3. Dana

    Dana In the trades

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    As Tom correctly points out, two 180,000 BTU/hr boilers for a 6000' house is a ridiculous amount of oversizing even for a sub-code house, let alone a new code-min house. Seriously, 360,000BTU/hr is is 60 BTU/hr per foot of conditioned space, a ratio that would make sense only for barely-insulated 2x4 house in Fairbanks AK.

    Also 10 zones on 360KBTU/hr of boiler is guaranteed to short-cycle the hell out of those boilers, cutting into both lifespan and efficiency, independently of their AFUE rating. Even a 120gallon buffer tank won't necessarily save you with 360K of burner driving it.

    The first order of business is to get a credible room-by-room/zone-by-zone heat load calculation. Most code-min 6000 houses these days can be successfully heated at 0F outdoor temps with a single 100,000 BTU/hr boiler.

    What fuel?

    Got a ZIP code? (For outdoor design temp purposes.)

    How is the hot water being heated, and are there any big spa tubs or luxury 6 side-spray gusher showers to tell us about?
  4. Soapm

    Soapm New Member

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    Sorry to chime in but I love reading these guys advice, and it seems the best advice is change contractor or installer... ROFL...
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Are they planning snowmelt on a long driveway or big parking lot? That's some serious amount of heat. Now, this is probably 5-6 years ago, when I was looking at boilers, I was looking at a WM and some other boilers...while the place I ended up buying mine from had installed some of those, he refused saying they had too many problems. I ended up with a Buderus unit. No personal experience with WM, and even if they had had teething problems with that model, I'd expect they'd have fixed them by now. The brand has some importance, but the quality of the installer is probably more important. An overly large unit usually won't meet its energy efficiency rating.
  6. Dana

    Dana In the trades

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    My advice itends toward doing at least the napkin-level math yourself, then either make the contractor show his or make them do it your way if it diverges by a huge amount. Not all plumbers are competent hydronic designers, even if they have some experience at installing the equipment. It's possible to do a good job at the installation, even if clueless as to how to spec the equipment (and conversely.) This one really screams for a design review by a competent designer, even if he sticks with the contractor for the installation. With a dozen zones and two boilers it's gonna take a pretty big napkin to put arithmetic bounds on all of it.
  7. Tom Sawyer

    Tom Sawyer In the Trades

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    With a dozen zones and was it two boilers? I want to be the guy that sells and installs it even if it is oversized and way more complicated than it needs to be. I have a kid going to MIT next fall, I need the cash LOL
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