Need advice on converting from oil to natural gas.....combis?

Discussion in 'Boiler Forum' started by Edgeman, Feb 22, 2013.

  1. Edgeman

    Edgeman New Member

    Messages:
    15
    Location:
    CT, United States
    Thanks everyone for your help. Sounds like a good plan that I will be going with. The contractors all want to talk you up in BTUs and Indirect size. One wanted 110 with a 60 gal indirect. I think they make more money the larger the installed system.
  2. Edgeman

    Edgeman New Member

    Messages:
    15
    Location:
    CT, United States
    Upon oil to gas conversion, getting rid of the 275 heating oil tank?

    The 5 year old 275 gal heating oil tank is above ground and in a shed next to the driveway. The gas contractors are quoting me anywhere from $500 to $750 to remove it from my property.

    Being that it is above ground, is it ok to put on on craigslist list to get rid of it? The previous owner had to remove the in ground tank when I bought the place 5 years ago. He had the new one installed. I figure perhaps i can sell it for $100 or at least give it away to avoid the onerous removal fees. The town only has restrictions and laws for removing in ground oil tanks. The tank looks new and i expect i to be near empty in mid April when I do the conversion. There is currently 140 gals to get me through 6 weeks in coastal CT. Thoughts?

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    Last edited: Mar 2, 2013
  3. Edgeman

    Edgeman New Member

    Messages:
    15
    Location:
    CT, United States
    Most of my contractors are insisting on the TT110 rather that the TT60.

    "The 110k will not Short Cycle it is designed to modulate, these boilers run on low fire 80% of the time. You will need 110k BTU with your hot water demand setting the tank high will causing scaling and other problems. We have been designing systems for years and are good at it, we also see a lot of poor designs."

    "We don't set up the boiler with priority, as you may now, when the hot water demand is calling the boiler will not produce heat for the home. I also seen in the past in the event the hot water heater malfunctions for example, if the pump fails the demand for hot water will never be satisfied therefore the boiler will not switch over to heat. The same goes true if the aqua stat fails on the water heater the boiler will never switch over to producing heat. Having siad that if you insist and you want the TT60 I will quote it for you. I feel very comfortable and confident with the 110, it will not short cycle due to the turn down ration, but I want to make sure you are happy. I will email you over the quote for the 60 on Monday."
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    22,273
    Location:
    New England
    Using a bigger boiler to accommodate an indirect as a 'normal' zone is a big mistake. His observations are correct, though, but they occur so rarely, that it's not worth the long-term continued expenses. Those boilers have a modulation range...the bigger one's smallest fire is near your worst case coldest day. Those occur so seldom, it would rarely be in condensing mode.
  5. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

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    Location:
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    Any boiler that is over-sized will short-cycle.

    Many of the contractors that never did a proper Manual 'J' heat load in the past, feel even more comfortable not doing their job since the advent of the modulating gas boiler about 10 years ago. If the total load, or a high-load zone, that the ModCon serves, can't "unload" the Triangle Tube Prestige110 at its lowest output (28mBtuh) it will shut down the boiler and cycle on and off, "bumping off the bottom". We find this is the case more often than not in the ModCon systems we have not designed. Of course this will happen under full-load, i.e. the coldest few days, so that in warmer weather (the other 360 days of the year) when the boiler should be running cooler, condensing more and producing more comfort with less gas, it is actually cycling on and off losing its full potential and giving the ModCon an ill-deserved reputation for under-performing and expensive maintenance. All engines want to run. Like stop and go traffic an over-sized boiler starts and stops, using more fuel and wearing out faster than it should.

    Domestic hot water is almost always prioritized since it allows the use of a boiler properly sized to the heat load and almost never over-sized for the 20 minute peak load of the typical domestic hot water heater. Whereas, it may be true, that the space heating will be "locked out" if the DHW is not satisfied for some reason, it is irrelevant to the homeowner who will not go without either for long.

    If you don't, or won't, do heat loads and will not prioritize DHW (necessitating, by definition, an over-sized boiler, running too hot for anything but fin-tube baseboard during design conditions) the only boiler for you is the IBC 15-150. In fact just reading the IBC installation manual will give most "experienced" boiler installers a new education. But I digress.

    How sweet it was in the old days, when boilers were made out of cast iron, could be double-sized, burn twice the fuel, any pump would do, as many zones as you want, run to 200°F all-the-time, with a mind-less-tank-less coil making DHW as fast as you could turn the faucets on, and nary a thought to the how or why, just do, do, do and be done.

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

    Dana In the trades

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    Listen to the Badger- oversizing the boiler is paying too much to end up with lower efficiency and a shorter boiler life!

    The simple-math model goes something like this:

    The Solo 110's min-mod output even a a higher non-condensing temperature mode is about 25,000 BTU hr or higher, (considerably higher than min-mod on the Solo-60). On a low mass stick of heat emitter like the 50' of fin-tube baseboard it would only balance at 500BTU/foot. Take a peek at the spec sheet for a random popular baseboard model. Note that it takes 160-170F average water temp (AWT) for the baseboard to get that 500BTU/foot into the room. When outdoor reset control (ODR) is calling for a lower temperature, it will definitely cycle- the only question is "how much?". You can push the temps lower a bit but not too much. As long as the burn lengths are at least a couple or three minutes long, and only a handful of burns per hour and it won't trash the boiler. But can you get it low enough to condense? Not even:

    You need an AWT of under 125F to break 88% efficiency on a mod-con, and even if you could program the hysteresis on the ODR to 20F (letting it overshoot the curve's setpoint to lengthen the burn) there is nowhere near enough thermal mass on the 50' baseboard zone to yield burns that are long enough to not eat up all the condensing efficiency in ignition & flue-purge losses, (and add a lot of wear & tear on the boiler to boot.) At an AWT of 125F you're looking at about 12K being emitted by the fin-tube, and about 28K being delivered by the boiler- it'll short-cycle, guaranteed.

    BTW: If the ~41K heat load calc was done with SlantFin Hydronic Explorer, that tool is known for having some of the highest oversizing margins out there- 25-35% over measured heat loads. Assuming that the 41-42K number is at least 1.25x reality (a pretty good assumption, 42,000/1.25= 33,600BTU/hr, which is also a credible number. With 180' of baseboard in the whole house that's under 200BTU/foot, so it looks like you could even run the thing with a fixed-output temp of 125-130F and be in condensing mode all the time, and never be cold, as long as you don't short-cycle it to an early death on zone calls. With fin-tube the output of the heat emitters has non-linearities that make output somewhat unpredictable if you tried to run a AWT of 100F, which would make tweaking in the ODR curve difficult & paradoxical, so you'd probably want to set the floor of the curve at 120F anyway. But since you'd still get design day heat into the house with 130F output it'll be a pretty short curve- still worth doing. With 50' of fin-tube and 120F out/100F return for a 110F AWT the fin tube would deliver on the order of 8000BTU/hr, or about half the min-mod output of the Solo 60. With bigger programmed hysteresis you can probably keep it from short cycling, but you may have to experiment a bit when dialing it in. Ideally you'd get at least 3 minutes of min-burn when serving the single zone, but as long as it's only of handful of burns per hour it won't much matter. If the burns are under a minute it's something of an efficiency disaster, and you'd do better to bump the temp up 5F or even 10F if that's what it takes to get at least 100-150 seconds of burn out of it at a time, even at low-low duty cycle.

    Bottom line- the TT-60 or similar will be able to work reasonably with your zoned baseboard, whereas the -110 would not- it's too big to heat your house at condensing efficiency. Any fixed-output boiler with even 40K of output would never run in condensing mode without either adding a lot of thermal mass or more radiation to the system to stop the short-cycling (buffer tanks, or more massive radiators like radiant slab floors.) Higher-mass boilers would ideally see 10 minutes of min-burn since they incur higher standby and cycling losses than low-mass mod-cons.
  7. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    Minimum flow rates? The lack of basic hydronic field knowledge in the hydronic field is astonishing.

    First, a Manual 'J' heat load to properly size the boiler to the "block" load, which does not change. Once the size of the boiler is determined you may measure the baseboard to confirm that you have enough radiation to unload the selected boiler. This is also an excellent time to measure the fin each zone. The smallest,shortest zone will determine how often the boiler may cycle an if you go for the 100mBtu units you will see some serious "bumping off the bottom".

    In most homes a condensing boiler properly sized to the heating load, coupled with a indirect, properly sized to the DHW load will yield the most efficient, reliable and comfortable system available today. If you can't find a local contractor to perform this critical first step, find a hydronic designer that can specify the equipment for the local contractor to install using the skills they should have. Ask to see a picture of one of their condensing boiler installations and a sample of a heat load they have performed.

    No heat load, no job.
  8. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,456
    Location:
    Houston, TX

    There are plenty of scrap metal places that will pick it up for free.

    You may be able to have someone take it for scrap and split the money they get for it. Or take it yourself.


    If it was me, I would keep it. You never know when it may become handy. Extra Fuel is nice to have in a emergency.
  9. Edgeman

    Edgeman New Member

    Messages:
    15
    Location:
    CT, United States
    Thanks for your input, guys. Looks like the TT60 with a Smart 50 is the way to go. For the extra $200 I get a 10 gallon margin over the Smart 40 to cover the DHW.
  10. Dana

    Dana In the trades

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    DO take Morgan's advice about finding a competent designer/installer, if you can. The more idiot-proof systems & choices get, the more creative the idiots seem to get. I'm positive there are plenty of fools capable of screwing this one up, even with all of the right components in hand.

    Anybody advising a 110K boiler for a ~2000' raised-ranch in CT moves to the "creative idiot" column in my book, unless they can show their math and it actually adds up. For the real heat load to actually be higher the non-condensing output of the TT-60 would take multiple code violations on window type & window/floor area, etc. Even the lipstick-on-mirror type math I've laid out about cycling on zone-call issues shows how bad a choice that would be, and I'm not a professional hydronic designer (though I've de-bugged, dialed in, and designed more than a handful systems at this point- everybody has a hobby, right? :rolleyes: ) There are code-min 2000' houses in Fairbanks AK that wouldn't need the -110 (but with a design temp of about 40 below zero you can bet there are some that might.)

    Sure, if you cranked the temp way up the -110 wouldn't short cycle in your house- you'd always be warm and never run out of hot water, but it'll never hit it's AFUE numbers. With the -60 there's a very good chance that it will, and the heat will be more even.

    Unless you have a bigger than standard tub you probably don't need the 50 gallon HW heater either. A 40 gallon tank with over 50K of boiler output recovers VERY quickly (a typical standalone 40 gallon tank has about 30K of burner-output behind it, and that's probably the most common size & type of HW heater in the US), but the "extra" 10 gallons never hurts. Rather than spending an extra $200 in hardware for maybe 20-25% more showering capacity, a $400-600 drainwater heat recovery heat exchanger would more than double it (!), and even the -60 would be able to deliver literally endless showers (especially with your low-flow shower head.) I have a 4" x 48" version on my system and a ~3gpm shower head and even with all zones calling for heat with someone in the shower (not priority-zoned), the output never modulates over 60K. It does nothing for tub fills, but it's like having another 25-40K (depending on flow) of burner behind it in shower mode, but it's "burner" that uses no fuel. From a fuel cost savings point of view it would take forever (at least a decade for a 2-person family) to pay off at current natural gas pricing, but for oil-burners it pays off pretty quickly.
  11. charlie p

    charlie p New Member

    Messages:
    17
    Location:
    New Jersey
    I was going to start a new thread ,But your thread(Edgeman) is pretty much my same situation.
    I actually went out and bought a weil mclain ulta 155 because thats what the HVAC guys said I needed,then while doing research on installing I found out it was way oversized.
    I have a 2000sf house in the mid-atlantic(NJ)
    Currently have a 100k weil-mclain oil,which when it was put in they oversized it,the one befor that was 80K.
    HVAC guys come in look at your heater and say it needs a bigger one
    Its a vicous cycle 80k to 100k and almost went to 155K (thank god for the internet:D)
    hotwater baseboard,3 zones includeing the DHW boilermate tank
    Heatloss @55k
    Ok so Im returning the Ultra155 ,
    I was giong to get the 105 Ultra but after reading this thread I'm wondering if the 105 should be knocked down to the Ultra 80,or is that still OVERKILL
    I will be adding another 3-400sf within a year or 2
    Edgeman
    Around here those tanks sell
    I just sold one that was 5 yrs old for $250
    another older one with surface rust sold for $100
    Youd be suprised how many people want or need them

    It nerve racking going from 100k to 60-80k
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,273
    Location:
    New England
    Take a cold day, see how much the boiler actually runs in an hour. If it runs say 10-minutes, you're getting 1/6th of its total output, and actually less, if it cycles a few times since some is lost out the flue each cycle.
  13. charlie p

    charlie p New Member

    Messages:
    17
    Location:
    New Jersey
    Honestly,I have not a clue what you just said:confused:
    Would you mind puttting that in laymans terms
    Thanks
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,273
    Location:
    New England
    For your house to stay at a constant temperature, the amount of heat you put into it must be the same as what is lost. You're only putting heat into the house as the result of the boiler running. If it only needs to run say 1/6th of the time, it's likely as much as 6x too big for that exact time! On an absolute worst, coldest day of the century, if the boiler ran full time to keep the house warm, it would still be a little big, but not by a too bad of a margin (most proper sizing looks at the worst 90% day, not the 100% or the odd 110% of normal worst day - IOW, most recommend a boiler that can keep the house at the desired temp 90% of the time on the worst day in a 25-year period - the rest of the time it can keep up, and on a really cold day, maybe lose a degree or two at the coldest part of the night which is not normally a big deal). There's nothing wrong with a boiler running full tilt on a very cold day. There IS a big problem if it can't run very long during that same day. As a very rough WAG, time how long the boiler is running on a very cold day during the coldest hours. If it's not on most of the hour, it's likely too big.
  15. charlie p

    charlie p New Member

    Messages:
    17
    Location:
    New Jersey
    Now that I understood
    Thank You
  16. Dana

    Dana In the trades

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    2,986
    Location:
    01609
    I replaced a ~125K output system for something that deliver no more than 44K running flat-out on a ~2400' 1920s bungalow (plus ~1500' of semi-conditioned insulated basement) in Worcester MA, and it stays comfortable even at -8F outdoor temps.

    If your house actually has insulation in the walls & attic, glass in the windows (either double-panes of any vintage, or storm windows over antique single panes, like mine), I'd be shocked if you needed even 60K of output, even if you have an uninsulated basement or crawlspace. If you give me the total square feet of windows (and their U-factor if known, description of not known), the total amount of wall area and construction type/R-values (less window & door area), and the total amount of attic area & R-value, it would be pretty easy to do an I=B=R spreadsheet type heat load calc, which is usually an upper-bound.

    The 99% outside design temps in NJ run between +10F and +15F, and even if you had a boiler for the heat load at EXACTLY the design temp you'd never wake up to a cold house.

    At 60K you'd be talking 30BTU per square feet of conditioned area, which might be typical of older code-min construction in Fair banks AK (outside design temps in the -50s F.) More typical for the mid-Atlantic would be between 10-15BTU/foot of conditioned space, so a 60K-out boiler could easily be 2x oversized or more.. But heat loads are NOT a function of floor area, they're a function of exterior surface area, air leakage, and the inside & outside temperatures. An I=B=R calc would at least find the right ballpark, and 100K ain't it, guaranteed.
  17. charlie p

    charlie p New Member

    Messages:
    17
    Location:
    New Jersey
    Hey Dana
    Thats funny:DYES I have found that out
    Thanks for your help.
    As I said in the first post ,,,it's nerve racking going from 100k to
    60-80k especially when there's 3 different heating guys saying "GO BIGGER"
    Not one of them did a heatloss.
    My heat loss results came out Roughly=
    UA(BTUhr-F)=851
    DesignLoss=55293
    year loss=102.1
    Fuel cost=$1276(10year=$20327)
    Thats with window doors insulation
    Design Loss set at 0
    infiltration=1.25
    doors=63sf
    windows(half single pane,the rest double)=225sf
    walls -1250
    ceiling-2200


    What I'm finding out is ,
    I want to size up my heat loss to match the NET IBR RATEING,Right?
    If that's the case the 80 would be my boiler of choice,Right?
    The NET IBR of the WEIL MCLAIN ULTRA 80 is 62, AGA Input= 80, DOE=71
    Whereas the 105 ultra is Net IBR123, AGA=105,DOE=94
    And the original 155 is just crazy off the charts
    The 80 would actually be alittle big but it will give me some room for a 3-400sf add-on

    It just floors me that these guys are the pros:confused:
  18. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,273
    Location:
    New England
    They don't have to pay your fuel bills! They don't want you to ever call back and say the boiler can't keep the house warm...so, the easiest (and most profitable for them!) is to specify one too big. Only if they have any true understanding and training and pride in providing the right thing are they likely to provide the best solution. Plus, it's often hard to explain to a customer (they're always right, now, aren't they) that they've lived with say a 150K BTU boiler, but they really only need one less than half that size...it's a sorry circle. Many people don't want to take the time to learn enough to get it right; much easier to just do it the same old way.
  19. Dana

    Dana In the trades

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    First, there is NO location in NJ with a 99% design temp of 0F, and it's silly to design to 0F. Coastal areas run about +15F, interior and higher elevation about +10F. Even if you sized it EXACTLY for +10F on an I=B=R heat load you would have margin, due to the internal heat sources and the other factors like curtains & shades, the non-linear improvement in performance of windows and fiber insulation with falling temps. Yes it does get to 0F or below sometimes, but the thermal mass of the house and the internal heat gains of hot-bodies & plug loads mean you don't really lose ground.

    Using an outdoor design temp of +10F and an interior design temp of 70F, that's a 60F delta. Assuming your I=B=R calc at 851BTU/degree-hour is correct, that's ~ 51K of load BEFORE you start subtracting of internal heat sources. Every sleeping human is worth ~250BTU/hr, each refrigerator is worth about 200BTU/hr, then there's all the parasitic plug loads (got a Tivo?) it adds up. I'm guessing you're probably between 45-50K at +10F.

    Adding 400' of addition does not necessarily increase the heat load very much, since it doesn't add exactly proportionally to the exterior surface area, and even at IRC 2009 code min for U-factors and R-values, if it's displacing R11 batt-insulated walls with R13+5c.i. and U0.6 -U0.1 windows with U0.35 the heat load can even go DOWN(!).

    Do NOT use the IBR rated output unless your boiler is out in the garage, on the other side of an insulated wall. The IBR output rating is a fudge-factor that presumes the boiler's standby loss and distribution losses go somewhere else. If the boiler room and distribution plumbing is is located in a semi-conditioned basement or anywhere else inside the thermal & pressure boundary of the house, the DOE output is the most appropriate number.

    The Ulrtra-80 is still a bit overkill for your true heat loads, but since it can modulate down to 16K-in/15K-out, it'll work out OK, since it's min-fire output going to be less than half your design condition heat load. As long as your smallest heating zone can deliver the 15K at condensing temps (average water temp <<125F) it's performance will be AWESOME!

    If the 400' addition is going to be it's own zone, you have to keep that in mind- it may take something 2x the amount of radiation that it takes to heat the place to be able to shed 15KBTU/hr at low water temps without short-cycling the boiler. Most fin-tube baseboard delivers ~250BTU/ft @ 125F AWT, so you'd be looking at 60' for it to balance at min-fire, but the heat load of the addition zone itself might only be 5000-6000BTU/hr @ +10F, which could be readily heated with 25' of baseboard, but that would be a too-small micro-zone likely to cause short-cycling, robbing the boiler of what would otherwise be excellent efficiency.

    Single pane windows are typically U0.8 (wood framed with muntin bars), to U-1.1 (aluminum framed single-light sashes). It's well worth either replacing them with a code-min window or (for far less money) adding low-E storm windows (which will sometimes outperform a code-min replacement window.) Harvey makes the tightest storm windows in the biz, and has a hard-coat low-E option, but the better grade Larsen's sold through the big box store chains are pretty good too. It's on the order of a couple-hundred per window, but the installation labor is dramatically less than a replacement window. Low-E storms may be the most cost-effective load reduction you can make, but there are surely more.

    A heat load of 50K @ +10F on a 2000 house is on the high side (25BTU per foot of conditioned space), and most can be brought under 40K cost effectively with well targeted envelope upgrades. Air-sealing is the critical first step, followed by spot insulation where there are deficits or where it's easy to add more. The single-largest air leak in most timber-framed homes that haven't already been through a round of blower-door verified air sealing is often the band joist and foundation sill, typically more leakage than all of the windows & doors combined, and being at the bottom of the house, a more important leak due to the stack-effect draw. Air sealing all attic penetrations also looms large on the list- plumbing stack & flue chases, electrical penetrations, etc all add up to significant stack effect losses. At 0.18BTU/per cubic foot degree-F every 10 cubic feet per minute count. (10cfm=600 cubic feet per hour, and at a design delta-T of 60F that's 3600 BTU/hr. If you have 20 cfm of stack-effect leak (which isn't out of the question, even common for 2 & 3 story houses) it's more than 10% of the total design condition heat load. Don't worry about making the place "too tight" for human health- it's actually pretty difficult to achieve that level of tightness in retrofit without a full-gut rehab and a concerted air sealing effort. Tight is always right- if you end up with 40%+ indoor relative humidity even during January cold snaps, then it's time to think seriously about mechanical ventilation (or reducing the size and number of tropical house plants you keep. :) )
  20. DonL

    DonL Jack of all trades Master of one

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    Location:
    Houston, TX

    Dana,

    You write some good stuff.

    Do you have a book that you wrote. ? You should, I would buy it.

    Nice Work.
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