Need help to evaluate offers to replace a boiler

Discussion in 'Boiler Forum' started by 1077, Apr 7, 2011.

  1. 1077

    1077 New Member

    Messages:
    3
    Location:
    Trumbull, CT
    I am told I must replace within a couple of months the boiler in my 2,400 square feet 34 year old house, with 2.5 bathrooms, replaced windows, good insulation, etc. I have 4 bedrooms and we are 2 people still living here. Most likely we will have to sell within 3-5 years and move into something smaller. Apparently the steel boiler has developed some cracks; I did not see them, but the heating company man showed them to my wife.

    The unit to be replaced is a 10 years old New Yorker AP-790 with a heating capacity of 149 MBH. It has been satisfactory: excellent on heating (2 zones) but could use a bit more hot water as I like to soak in the tub... but not vital.... Never had any major problems with two showers going at the same time even with two kids in the house and frequently a house-full of guests.

    Got three offers:

    1. A Burnham V84 at 159 MBH for $5,500 installed. A new expansion tank is included (capacity not mentioned) but I am not sure if this is the same as an indirect water heater. Lots of sundries included as well which I assume should be standard for any installation.

    2. A Weil-McLain WTGO-4 at 145 MBH for $5,200 installed, Extrol tank (whatever that is - probably similar to the expansion tank) and again a slew of sundries.

    3. A Buderus GB125 BE/30 at 102 MBH (only 100 MBH in catalog for 178/140 degrees Fahrenheit) for approx $ 11,400 plus two programmable thermostats Honeywell FocusPro 5000 at $350 each. Offer not finalized and an alternative for a GB 125 BE/22 at 75 MBH for approx. $9,600 is also under consideration. Wonder if I will ever amortize the price difference by higher efficiency and lower size on the Buderus... but that's for me to decide. This contractor came with a heat loss calculation showing 43,083 BTU. He used the data available publicly on my house. Even had a picture of the house (!!??).

    My question: I understand that at an average rule of thumb a 20-30 BTU/H/sqft loss is reasonable, so all I would need is a 72 MBH unit... or less... as a minimum. Have I been running too big a unit for all these 27 years I spent in this house, throwing money down the drain for too much oil? Or is the Buderus guy trying to sell me be a bill of goods?

    Someone recommended looking into a Burnham MPO-IQ84 or IQ115 (could not find on the Internet any pricing info compared to the Burnham V84). It sports an 87% efficiency vs. Buderus's 91-93%. Someone else suggested using an indirect water heater and yet someone else believes that the steel tank is a lot better than a cast iron one and that the cracks that the service man showed to my wife were in the “refractory†rather than the steel… implying an ethical problem with the service man? This latter point tempts me to approach the BBB… but would hate to do so on a simple hunch.

    I am a former mechanical engineer (not in HVAC) so I am capable to understand the concepts but since I have been doing something else for the last 25 years, the terminology is somewhat foreign to me. A word from anyone who knows (a lot) better than I do what this is all about, and a suggestion as to how I could get an HONEST opinion, would be very much appreciated.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,990
    Location:
    New England
    It is not uncommon for older units to be 3-4x oversized. Do not use the x BTU/sq ft as it is not very accurate. Depending on how the domestic hot water was heated (internal coil vs indirect tank) would somewhat determine what you need for your hot water. 43K may in fact still be high. There are several threads on-going that discuss this, but one way to determine what your actual heating needs are would be to use your gas bill. The amount of energy you use run against the environmental information (how many heating degree days and similar info) can give you a very accurate indication of your exact situation, rather than a guess, as it takes into account the real insulation, windows, infiltration, etc. losses in your house. Anything else is an approximation. Some of them are really conservative.

    Keep in mind that the highest level of comfort results in the water temp used for heating to be adjusted and the boiler running 100% of the time. A mod-con can do this, a single burn rate boiler can't. Your old system probably short cycled itself to death.

    Whether a mod-con would pay for itself over another technology depends on the cost of fuel. I doubt it would pay for itself in 5-years, but may make the place easier to sell.
  3. Tom Sawyer

    Tom Sawyer In the Trades

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    Location:
    Maine
  4. 1077

    1077 New Member

    Messages:
    3
    Location:
    Trumbull, CT
  5. Dana

    Dana In the trades

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    2,836
    Location:
    01609
    Unless yours is the leakiest least-insulated late '70s house in CT your heat load at 0F will be well under 72MBH in the Bridgeport area, and if it's been tightened up at all it's probably under 40MBH. You're very likely 4x oversized, and operating a mid-80s efficient boiler at ~60% efficiency due to cycling & standby losses.

    Oversizing the boiler for it's peak space heating load by more than 1.5x will cut it's average efficiency dramatically, but is often done with embedded coil units to be able to keep up with much higher domestic hot water peaks. ( A couple of simultanious showers will be over 100MBH in winter.) A better solution is to "right size" the boiler to the space heaing load, and run an "indirect" - a hot water heating tank with an internal coil using boiler water to provide the heat.

    Keeping a boiler at a higher temp in standby than is necessary for space heating just to be able to provide enough hot water on an intermittent basis is also a huge efficiency hit. It's better to let the boiler cold-start, and purge heat at the end of each burn cycle either into an indirect or the heating load using an anticipating economizer such as the Beckett Heat Manager or Intellicon HW+, or the Energy Kinetics System 2000 steel boilers. System # 3 in this Brookhaven Nat'l Labs study was a System 2000.
    How fast the system heats your house from 60-72F is more a measure of the thermal mass of your house than it is of the steady-state heat load at the outside design temperature. With a right-sized or less oversized boiler it'll take much longer, and you might not want to use super-deep overnight setbacks (or program the T-stats to start up an hour before you get up.) Right sizing the boiler will more than make up in higher efficency anything you might have lost from a shallower setback.

    Every good design starts with a careful heat loss calculation, but the implied heat loss at 5F based on 850-900 gallons of fuel is in the 40MBH (==40,000 BTU/hour) range, not more. Even the very smallest oil boilers have higher output than that. I have a simliar sized circa 1923 house in Worcester MA (with an outdoor design temp lower than yours) with a measured 0F heat load no more than ~30MBH after insulating the basement and tighting up the place a bit. (If you haven't done a formal air-sealing assement/remdiation of the place or the basement isn't insulated, you probably ought to given the current and anticipated price of oil.)

    Since you're the engineering type, you might want to download an older version of Slantfin's Hydronic Explorer heat loss tool here an run your own heat loss calc:

    http://www.pvsullivan.com/Downloads.html

    The 97.5% design temperature for Bridegport is +9F, and that's the number I'd use. The 99% number is probably 5F, but the Slantfin tool overestimates reality by about 35% in most cases- PLENTY of margin for using the 97.5% design temp. If the boiler is 2x oversized per the Slantfin number, it's likely to be 3x oversized from REAL heat loss number.

    To use the fuel use (which is a MEASUREMENT, not an estimate), assuming the burner boiler is ~85% efficiency at steady state, and using 900 gallons and 140,000btu/s gallon, and Bridgeport's annual ~5500 heating degree days(HDD):

    Boiler's annual output= efficiency x gallons x btus/gallon= 0.85 x 900 x 0.14MBTU= 107MBTU

    to support 5500HDD, or 107MBTU/5500 = 19.5KBTU/HDD.

    There are 24 hours in a day, so thats 19.5K/24=812/BTU per heating degree hour.

    At 72 F indoors and 0F outdoors the implied heat load would be 72 x 812= 58,464btu/hr, or 58.5mbh.

    At a 9F outdoor design temp you're looking at (72-9) x 810= 51,156btu/hr or 51.2mbh

    Then consider the fact that you're probably using at least 20% of the fuel for hot water heating, so your design heat load would be 0.8 x 51.2mbh= ~41mbh.

    Then considering the boiler is more than 3x oversized for the load, it's as-used efficiency will be about 80% of it's steady state effieincy, and the real heat load at 9F is about 33MBH (with some squishy error bars.)

    Even the smallest oil boiler have something like 2x the 33mbh, or 1.5x the 41mbh number and more than 1.25x the 51.5 number. Even at 1.25x oversizing you'd be good down to down to about -7F (yup MINUS SEVEN) before it wouldn't maintain 72F and even at -12F all day long (during the next ice age?) you'd still be no colder than 65F. Since reality is likely be between 30-40MBH, you should be looking at only the very smallest boilers and set it up for cold starting with a heat purging control and using an indirect-fired tank for hot water, and you'd likely to be able to cut the fuel use to under 750 gallons/year. That 100-150gallons/year fuel use difference didn't matter as much at a buck, buck-fifty a gallon, but it sure does at $4+.

    If you ever think you'll break it up into more than 2 zones, or if one of your zones has more than 1.5x the heat load as the other (use the heat loss tool for comparative loss between zones) it may be better to use a reverse-indirect HW heater as a heating system buffer, but I won't go into that until you tell me more. (There IS such a thing as too much information.)
  6. 1077

    1077 New Member

    Messages:
    3
    Location:
    Trumbull, CT
    Ned help to decide which replacement boiler I should buy with which contractor.

    Dana: All I can say to your detailed response is WOW!! THANKS.

    I made some progress:

    Today I had an offer @ $7,576 by the Sears people for a Dunkirk 105 MBH boiler (believe it is model Kenmore KWX) with 7 years service and guarantee for parts and labor, annual inspection and 24/7 coverage transferable to the next owner. They sized the Dunkirk unit by measuring 120 ft of baseboards in the house.

    I narrowed down my choice to the Dunkirk and the $5,500 Burnham V84 at 159 MBH by a local contractor who was very prompt in the past responding to small repairs we needed done. Should I attempt to get from him a quote for the next smaler size Burnham V83 at 123 MBH?

    The heat loss calculation done by the Buderus rep. at 43,100 BTU heat loss seems to be born out by your comments, as well as by a rather rough calculation I made using the Excel spreadsheet offered at
    http://www.pprbd.org/plancheck/heat_loss.html
    but without entering all data required for each window, door, etc.

    Looking for comparisons, I found a website
    http://www.furnacecompare.com/boilers/burnham/reviews/
    where an equal proportion of overwhelmingly bad comments are "gracing" both brands.

    Can someone help me advance with my decision?

    Just for the record: the house is a 2,400 sqft, 34 years old colonial with unheated basement, located in Southern Connecticut. We lived here for 27 years and since it is now an empty nest we will likely have to sell within 3-5 years.

    In an effort to make their offer more competitive, the Sears people estimated that the boiler they proposed would reduce my current 850-900 gal/year average oil consumption by about 100-125 gal/year. They further suggested that, should I add about 10" of fiberglass to the 4" covering now my attic floor (about 1,200 sqft) for an R30 vs current R11 estimated at a cost of $1,900, I may cut our oil consumption by 20%. Do these two oil usage reduction estimates make any sense? As you say, at $3.77 for my latest fill-up, this does matter.

    I see the advantages of an indirect waater heater but there is no room for such a thing where the boiler is located and I am told by the Sears guys that that may cost me another $3,000 or so: hard to justify economically, especially with a 3-5 year time horizon, as it is highly unlikely that I could recoup this expense when selling the house.

    Although I am an "engineering type" as you say, I am deffinitely not a "do-it-yourself type", particularly when it comes to a big job like this. So increasing the number of heating zones is out as well.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,990
    Location:
    New England
    Why would you want a boiler triple your needs? It will not be anywhere as efficient as it could be. If you read any of the similar threads, you'd see that an oversized boiler is a very poor decision in both efficiency, longevity, and comfort.
  8. Dana

    Dana In the trades

    Messages:
    2,836
    Location:
    01609
    Since your REAL design day heat load is well-under 50K even the 105MBH Dunkirk or the 123MBH Burnham is ridiculously oversized, will short cycle, and will perform well under it's rated efficiency unless you add a buffer tank for more mass and heat-purging controls to reduce the idle losses of the boiler. The only rationale for 100MBH+ would be for the luxury of taking an endless shower in the dead of winter using the internal coil. But the high standby temp of the boiler in that operating mode KILLS it's efficiency, as do the cycling losses of a 3-4x oversized boiler.

    $3k installation price for an indirect is on the high side unless there are some serious installation issues that would require you to move the placement of the boiler & flue or something(?). Get some real quotes, coupled with a smallest-of-the-line (which will be both space and operationally efficient) boiler. If space is an issue, there are wall hung versions of some boilers & indirects, and even the tiniest indirect will give decent peformance with only a 70MBH boiler behind it unless you're filling a spa or something.

    Measuring the baseboard is in no way a valid method of measuring the heat load or sizing the boiler for a hyronic (hot water) boiler. Measuring the radiation IS the right way to size a steam boiler. If there's "too much" baseboard for the boiler output the return water temp from the baseboard may be below the condensing temp in the boiler (~140F return is the low limit for most) and damage it, but rectifying that condition with near-boiler bypass plumbing to protect the boiler is cheap & simple, and in EVERY hydronic designer's bag of tricks (or should be.) I'd scratch any contractor who used that methodology off my list (or take control of the design myself and MAKE them do the right thing.)

    Have the Burnham guy figure out if either the 3-pass MP0-IQ84 (or the V82) + indirect will fit the availble space and price it out. At least those boilers will be only on the order of 1.6-1.75x oversized, and more likely to meet their AFUE spec without having to redesign the whole system. Even the smallest version of V83 with the 91MBH output would still be more than 2x oversized, and the bigger 123MBH-out burner has an efficiency-killing 3x oversizing factor for your heating load. (The AFUE on the smaller V83 is 86% compared to 82.5% for the bigger one, but AFUE tests are at 1.6x oversizing, and lower-than-warranty water temps.) If you're really stuck on going with an embedded coil for the hot water, the smallest V83 burner has enough output to run a single shower, but not two in the dead of winter, but the high idle-loss of the high-temp standby is expensive. If there's ANY way to make an indirect fit (even a tiny one), that's the right thing to do.

    Increasing the number of heating zones is the WRONG thing to do unless you're setting it up to run with a buffer tank or buffering reverse-indirect, since that kills efficiency by short-cycling. At 2 zones of equal size, and a heat load of 43K, the heat load of any one zone is probably no more than 25K, which would make the 123MBH boiler about 5x oversized, guaranteed to lose efficiency to short cycling on zone calls. With a 70MBH boiler it's still going to run more cycles but the fractional loss of eash burn will be less eggregioius. I suspect the MPO-IQ does it's own heat-purge control, (which is how they can hit 87% AFUE), which will at least cut down on idle losses. If you go with a boiler with dumber controls, like the V82 an Intellicon HW+ retrofit is a $500 cost adder, but would pay for itself several times over in your time frame.

    Rather than 10" of additional fiberglass in the attic, go with 10-12" of blown cellulose. (Leave the existing batts, blow over them to a minimum total depth of 12", which would be ~ R40 total.) Batts always have gaps & compressions, and in a cold-side up configuration they lose R value BIG TIME due to convection within the insulation as the attic temp falls. Cellulose has much higher convection retardency, and it's R value even increases very slightly when it's 0F in the attic and 70F in the house. And blown fiber fills in all the gaps, etc. If you go that route insist on "stabilized" cellulose, which is more dimensionally stable (doesn't settle much over time), and uses only borates for fire retardents, which makes it less attractive to rodents (an eye-irritant to mammals, but low-toxicity), and kills ants/termites/wasps (borates kill the gut-flora protozoans needed for processing wood-fiber, killing the host insect via malnutrition. Insect-canabalism of the sick or dead then kills the whole nest with many species.) It's cheap stuff- get bids, but R38 of additional cellulose runs on the order of $1/square-foot of coverage, and there are likely subsidies to knock that back further. Performance-wise it's a measureable uptick over just adding a layer of R30 or R38 batts down. Meeting code on R-value would usually be recoverable in resale price of the house, since it's just one fewer negotiating point the buyer can push back on.
  9. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    "Measuring the baseboard is in no way a valid method of measuring the heat load or sizing the boiler for a hydronic (hot water) boiler."

    Dana1 is right as usual on this point, although I do see the merit in measuring hydronic radiation as we can prove that the current radiation will not support the gross output of the over-sized boilers proposed and disqualifies the Sears guys with their private label boilers (not hard to do ANY case).

    Professional hydronic heating contractors perform and produce computer generated heat load analysis before the boiler is sized or installed. If you can't find a competent hydronic or radiant contractor in your area, higher an RPA certified designer to specify boiler, radiation, water heater and draw up the near piping and controls strategy.

    http://www.badgerboilerservice.com/contractor.html
  10. Dana

    Dana In the trades

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    2,836
    Location:
    01609
    In southern New England where even at sky-high CT electricity prices, the performance of R410A refrigerant mini-split air-source heat pumps is good enough at these relatively modest design temps with low overall heat loads in some cases mothballing the boiler and installing mini-splits make sense. In CT the operating cost of a mini-split at 18cents/kwh is still under a best-in-class (but of-necessity oversized, since they don't make them under ~60KBTU/hr) new school oil boiler even at $2.50/gallon oil. The upfront cost is often lower than a fully commissioned new oil boiler too- at $4 oil the payback can be under 5 years.

    The mini-split project I analyzed most-recently was in zip 01610, using Mitsubishi Hyper Heat series, but there are many others, Daikin, Sanyo, Fujitsu etc. all with different heating vs. cooling specs, but most have a heating COP of ~ 2.7 @ 15F or ~1.8 @ 0F and 4+ @ 40F+. It's not a lot cheaper to operate than condensing gas in New England, but compared oil or propane it's hard to rationalize NOT going with these better-class heat pumps. In US climate zones 4 & 5 they will often meet or beat geothermal heat pump heating efficiencies, at a fraction of the installed cost.

    This guy's Buderus to Fujistu mini-split swap in a modest sized house on Martha's Vinyard sure paid off in spades:

    http://blog.energysmiths.com/2011/03/out-with-the-old-in-with-the-new.html

    (Lessee, ~2 gallons a day, vs. $2/day in mid-winter- which works out the best at $4/gallon?)

    They're clearly not for every application, but I'm really warming up to mini-splits!
  11. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    I love my mini-split but would not give up the unmatched comfort of hydronic heating.

    Most of my work is replacing old low-efficiency boilers in older homes with high efficiency (condensing) boilers coupled to indirect-fired water heaters.

    In your case high efficiency is not practical unless you think it will increase the value of your home for resale. Given the modest size, I doubt it. Gross fuel usage and degree days are of limited value as the boilers is sized for the coldest day of the year published by ASHRAE in their Fundementals Handbook.

    An accurate bulk heat load analysis is in order, confirmed by measured radiation to assure the boiler is not too big for the radiation (the opposite is a good thing except in steam).

    Once you are comfortable with the size, go for the indirect as it will last longer and perform better than any alternative for the same money. I am assuming oil-fired boilers are being quoted.

    I really like the Buderus oil boilers but would not buy one for someone else.
  12. Dana

    Dana In the trades

    Messages:
    2,836
    Location:
    01609
    I hear you perfectly about the comfort of hydronic heating but at $3.50+ oil even 20 cent kwh electricity is dramatically cheaper when it's warm enough to hit a COP of 2.8 or better. That is literally most the time in Trumbull CT, where the January mean temp is ~28F there according, a temp at which most R410A minis have a COP over 3. The average January low is 22F, a temp at which they hit 2.9-ish. In that climate it'll beat most geothermal installations when pumping power is factored into the COPs for geo.

    Oil would have to be ~$2.50 to have comparable cost with an 87% Buderus, even if sized perfectly for the load, and would it need to be under $2.25 with 3x oversizing. Cranking up the temp a couple of degrees for higher comfort is still cheaper by far. (At some price the discomfort to the pocketbook overrides the creature comfort of oil-fired hydronic heat.) Maybe we'll see $2 oil again, but I'm not holding my breath.

    Natural gas hydronic heating is cost-competitive to mini-splits even at 80% efficiency at current local fuel prices for gas.

    With low temp radiation like radiant slab floors air-to-water R410A heat pumps like the Daikin Altherma cut it, but not as a retrofit boiler on a fin-tube baseboard system.

    Like I said, mini-splits are not the magic bullet for every application, but they're surprisingly versatile and efficient in a southern New England climate. They're definitely worth looking at in comparison to geothermal systems with more design issues to get right, and much higher installed cost, particularly for smaller homes with open floor plans (&/or high-R walls) and smaller heat loads, or as supplementary heat in homes off the gas-grid.
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