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Thread: new oil boiler - what to look for?

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    DIY Junior Member warm all winter's Avatar
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    Default new oil boiler - what to look for?

    We have a 1400 sq ft ranch. It's been insulated r13 walls, r40 attic, copper pipes with baseboards. We're replacing the 40 year old boiler. We'be gotten one quote on a buderus g215 boiler which seems hugely oversized. Is this because of the 40 gal indirect we are going to add? Actually every oil boiler out there seems oversized...even the cheesy method of 30mbtu/sq ft puts our heat loss at 40 or so. While I have been doing lots of reading this is still a daunting task. For our new system (one zone) what sort of options should we be seeing from contractors? I.e. any buffer tanks, outdoor resets, etc.?

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    In the Trades Tom Sawyer's Avatar
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    You can either have a heat loss done or size to the existing baseboard. The heat loss method is more accurate. Add NOTHING for the indirect load. It should be a priority call.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    Retired Defense Industry Engineer jadnashua's Avatar
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    One fairly reliable method to see what you need is to take your oil usage, figure the BTU equivalent from each gallon burned, and compare that to the degree-day history over the last year. This will give you a pretty accurate evaluation of what heat was necessary, and you can then size the new boiler accordingly. The discussion on how to do that can be found with the search function. The degree-day info for your zip code is available on-line. Real use is more accurate than a heat loss calculation.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member warm all winter's Avatar
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    Well, for better or worse all the insulation work was done over the summer, which makes comparing with last year's bills sort of hard! The smallest capacity boilers all seem to be in 80 MBtu range - if that comes out to 2x oversized or something, is it still going to work well if we install one? I have no doubt it'll operate more effectively than the old boiler, what i'm wondering is what is the most effective way to make the new boiler work with our size system. Some contractors did measure the house for accurate heat loss #'s but they haven't gotten them to me yet.

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    DIY Junior Member warm all winter's Avatar
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    I've used the Slant/Fin heat loss calculator and come up with a number of 42 MBtu for the heat loss. Some of the room dimensions were by memory so it might be +/- 10% on that.

    Speaking of Slant/Fin I was looking at the Eutectic EC-10 boiler (specifically the EC-13A model). This seems interesting - well insulated and triple pass, similar to the Buderus or Viessman construction. Are these worth looking into?

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    In the Trades Tom Sawyer's Avatar
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    I hate Slant Fin boilers but that's just an opinion based on having worked on the pieces of crap for over 30 years. Go with the buderus
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    In the trades Dana's Avatar
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    The slant-fin heat loss calculator always seems to overshoot reality by at least 35% every time I've used it. With any annual fuel use number (or a K-factor stamped on an oil bill.) One could derive a pretty accurate whole-house heat load if you really wanted to, but it's going to be well under the ~60KBTU/hr lower-limit with oil burners. Odds are you're at or under 30KBTU/hr at design condition for a true heat load.

    There are almost no 1400' ranchers anywhere in MA with heat loads high enough to warrant going with anything but the smallest of oil boilers in a line. There is never a need to up-size a boiler to handle an indirect in a single-family home. If you're 2x oversized that's not great, but it's not an efficiency-disaster if the boiler is inside the insulation boundary of the house. As long as you have enough baseboard out there on your single zone to keep the thing from hitting it's high-temp limit before the thermostat is satisfied you'll do OK. If you have 2x the amount of baseboard necessary to deliver design-day heat @ 180F (possible, even likely) it wont' short cycle, but you could be at risk of running the boiler in condensing mode, which would be destructive. At the very least plumbing in a boiler bypass with a ball-valve on it to tweak the return water temp to the boiler should be able to get the system to run at lower temp and still keep the water entering the boiler at 140F+ (preventing condensation in the boiler.)

    If you have access to natural gas, now's the time. Oil is going to have a continual upward pressure on price due to world demand for transportation fuels, whereas massive exploitation of regional shale-gas has completely changed the equation, even if all new power generators were gas-fired (which they ain't gonna be.)

    If you don't have access to natural gas, consider installing a ductless mini-split heat pump (which can also serve as a super-efficient air conditioner.) At current MA electricity and oil prices heating with a mini-split is less than half the cost of heating with oil, and in eastern MA you can probably do all or most of the heating with a mini-split. See: http://blog.energysmiths.com/2011/04...ng-system.html and http://blog.energysmiths.com/2011/03...h-the-new.html (This guy is on Martha's Vineyard, but if you pick right models they can work fine even in the coldest parts of MA.) At part-load and 30F+ degrees outdoor temps they're at least as efficient at geothermal heat pump systems, but are a fraction of the price. (A 2-ton version could probably handle your heat load, and would run under $6K, installed.)

    Even with the sweetest tiniest Buderus you're probably looking at over 500 gallons/year, and if your place leaks a lot of air you could be closer to 1000 gallons. If you can cut your heating costs from $3-4K/year to under $1.5K with a mini-split (likely), it's not long years to break-even on one of those.

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    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    Once again an accurate heat load analysis performed on dedicated software by an experienced hydronic heating professional is the answer. More than 150% of the load is considered bad practice. What to look for? The smart guy in your area. He will be one of a very few that can produce an accurate heat load on his own or ask his distributor to do it for him. He will measure the radiation - since it makes no sense to buy a boiler with higher output than than radiation can handle.

    It is not about the boiler so much as it is about proper size, installation, maintenance and local support. If you can't get the size and near piping locally, find a designer to advise and hire the local guy to do the rest.

    http://www.usboiler.net/products/boilers/mpo-iq/assets/literature.pdf

    http://www.usboiler.net/products/boi...literature.pdf

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    In the trades Dana's Avatar
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    The problem with oil boilers in smaller homes in not-so-cold climates is that they're ALL going to be more than 1.5x oversized. The tiniest MPO-IQ is still more than 2x oversized for my house (and the smallest of the G215s would be 4x oversized). And I'm in a somewhat cooler location than warm-all-winter, and the house is both bigger & less insulated to boot.

    A K-factor (heating degree days per gallon of fuel use) often stamped on an oil bill would yield a fairly accurate measurement of the heat load at any arbitrary temp- usually more accurate than any of the standard heat-loss tools, even if it leaves you in the dark as to the room-by-room numbers you'd still want if designing the system from scratch.

    Finding the right designer & installer is key- unless you've really been burning through 2500 gallons of oil/year any of the G215s are outlandishly oversized, so that's probably not the right company do be dealing with. Calling the boiler distributor for recommended contractors can be a good method- they know who is competent and installing a lot of their equipment (and who is constantly harassing the tech support over stupid stuff.)

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    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    "who is constantly harassing the tech support over stupid stuff"." heheheheheee Point well taken.

    When I worked on oil burners - many years ago - I often downsized a nozzle until output and smoke lined up...obviously not for the "sad sack" in question.

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    DIY Member tk03's Avatar
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    A few tidbits.
    boiler bypass with a ball-valve on it to tweak the return water temp to the boiler should be able to get the system to run at lower temp and still keep the water entering the boiler at 140F+ (preventing condensation in the boiler.)
    A boiler bypass is an acceptable way to do boiler protection. It is not the best but a good way. But with a boiler bypass it will not change the return water temperature. A boiler bypass bypasses the boiler it does not preheat the return water. A boiler bypass is cold return to hot supply. A system bypass the water would then bypass the system and add hot to cold return. Most cast iron boilers today want boiler bypasses due to smaller physical size and less water volume, where commercial boilers want system bypasses.
    The need for a boiler bypass is less important if the boiler is over sized as it will produce more heat than it can dissipate so the temp will get higher than the condensing tamp much quicker.
    I agree the K-factor is a great way to calculate the size of the boiler providing they are not making hot water via a domestic coil or oil fired water heater. How much does efficiency affect that calculation. If the old oil boiler had a 600f stack temp and the new one is 350f. The old boiler is 73% and the new one is 87%.

  12. #12
    In the trades Dana's Avatar
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    It's easy to put a range or an upper bound on the boiler's steady state efficiency in lieu of an actual measurement, and ignoring the DWH load of a boiler with an embedded coil or indirect and including that in space heating load would still not oversize by more than 10-15% using a K-factor on a mid or late-winter oil bill. And on just about any 1400' house in eastern MA even if you assumed 85% for the old wreck and ignore the hot water component you're still gonna come in WAY under the output of the tiniest oil boiler.

    Coastal MA is about a 5600-5700HDD climate, with a design temp of +10F. If you're burning 1400 gallons/year (a gallon per square foot per year) in an 85% burner that's ~19.3 MBTU source fuel into the system in the course 5700 HDD, or 33895BTU/HDD which is 1412BTU/degree-hour (base 65). At a design temp of +10 you have 55 heating degrees, or a heat load of ~78KBTU/hr source-fuel. At 85% efficiency that implies a heat load of 0.85 x 78K or 66KBTU/hr, which is about the output of the smallest-of-the -ine oil boilers.

    But the only way to use that much oil in a 1400' house is to crank it up to 80F and leave some windows open to cool off. Most homes that size in easter MA are using 500-800 gallons, (even with the rusting old hulk running at 75% on it's best day) which implies a true heat load of about half or less of the smallest noo-skool boiler. (The smallest MPO-IQ has a DOE output of 74K, I=B=R, of 64K, so it's 2x oversized even if the boiler's out in the garage rather than in the basement.)

    With K factor and the boilers nameplate ratings, along with a few educated guesses you can get there using the NORA FSA calculator tool (based on boiler modeling work done at the Brookhaven Nat'l Lab) with a bit more precision, but it's not going to tell you much that you don't already know from the simple arithmetic: Any oil boiler is going to be 2x oversized or more for that house (unless you ship it to Fairbanks or Whitehorse or someplace even colder.)

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    DIY Junior Member warm all winter's Avatar
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    Thanks for the replies everyone, I appreciate your expertise. Regarding heat pumps - one reason I want to stick with baseboard heating is because it's allergy friendly, i.e. doesn't blow dust around like fan blown air does. I'm guessing that heat pumps don't produce high enough temperatures for baseboards. There's no gas service where we are. I think we'll be sticking with oil for this upgrade, even if it's not the final word in efficiency. Now, if I ever build my own house I'd put my $ into passive solar design and geothermal heat pumps...maybe someday!

    I've got all my quotes together. One thing I've noticed is a wide spread on prices. The pricier guys do blower door tests during the installation to make sure they've got the right sized nozzle on the burner, add a water softener to the closed loop, include a boiler stand, fresh air intake, etc. The message I've gotten loud and clear from everywhere I've looked is that the quality of the installation and maintenance support is more important then a few dollars in installation cost. Are those types of extras worth an extra 20% on the cost of the install?

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    In the trades Dana's Avatar
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    Quote Originally Posted by warm all winter View Post
    Thanks for the replies everyone, I appreciate your expertise. Regarding heat pumps - one reason I want to stick with baseboard heating is because it's allergy friendly, i.e. doesn't blow dust around like fan blown air does. I'm guessing that heat pumps don't produce high enough temperatures for baseboards. There's no gas service where we are. I think we'll be sticking with oil for this upgrade, even if it's not the final word in efficiency. Now, if I ever build my own house I'd put my $ into passive solar design and geothermal heat pumps...maybe someday!

    I've got all my quotes together. One thing I've noticed is a wide spread on prices. The pricier guys do blower door tests during the installation to make sure they've got the right sized nozzle on the burner, add a water softener to the closed loop, include a boiler stand, fresh air intake, etc. The message I've gotten loud and clear from everywhere I've looked is that the quality of the installation and maintenance support is more important then a few dollars in installation cost. Are those types of extras worth an extra 20% on the cost of the install?
    Unlike ducted heat pumps, mini/multi-split systems don't have air handlers & ducts. The most efficient versions have continuously variable speed blowers on the interior units, as well as continuously variable compressors. In an eastern MA climate they will meet or beat geothermal systems on whole-system efficiency whenever the temps are 25F or higher, at a tiny fraction of the installed cost.

    The downside is that they only heat the rooms that have the interior unit(s), but if yours is a reasonably open floor plan, keeping the "cozy zone" at 74F with the mini-split may be enough to keep the rest of the place in the high-60s or higher, but this would be a design judgment.

    At 10F or lower heating with the mini-split starts to look more like that of the oil boiler, so it's not a disaster if the boiler has to pick up the load at the extremes, but between 15-25F every BTU you get out of the mini-split costs less than half what it costs with the boiler, and at 45F it'll be 1/3 or less- a real discount.

    Daikin "Altherma" hydronic heat pumps are indeed pretty inefficent at 120F and above output, so it's not a good match for fin-tube. It can be OK with cast iron baseboard if you have enough of it, but it's really designed for true low-temp radiation like euro-panels or radiant floor slab.

    Even the smallest nozzle will still be 2x oversized for your heat load, but the blower door tests in conjunction with AIR SEALING is a worthwhile expense. See if you can't find an insulation contractor who offers blower-door verified air sealing as a service (they're out there).

    [edited to add]

    Geothermal is highly oversold in this climate, given the current state of the art of mini/multi-split efficiency. For less than $10K you can get a 4-zone 2.5 ton multi (for ~$5K you can get a 2-ton single head mini), whereas a properly designed geothermal system is going to start at ~$25K, and carries some design risk. Even if the well-designed geo gets an average COP of 3.5 when air-handler power is included, and the mini-split only gets between 2.5 & 3.0, for the $15K+ delta in cost you could install grid-tied solar photovoltaics that can make up the difference in power use. When it's 45F+ out a better-class $5K mini-split will usually beat even the best of the geo systems on raw system efficiency.

    Key to getting the most out of them is to "set and forget", since they run most-efficiently at 1/3-1/2 load or less- if you turn it down overnight it'll have to run full blast on the recovery ramp, and you lose more in make-up mode than you save by turning it down.
    Last edited by Dana; 12-05-2011 at 03:08 PM.

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    In the Trades Tom Sawyer's Avatar
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    Dana, Mitsubishi is making a ducted version now that they claim is still efficient below zero. It's pretty pricey though.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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