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

  1. #31
    DIY Junior Member charlie p's Avatar
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    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)
    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

  2. #32
    Retired Defense Industry Engineer jadnashua's Avatar
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    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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #33
    DIY Junior Member charlie p's Avatar
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    Quote Originally Posted by jadnashua View Post
    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.
    Honestly,I have not a clue what you just said
    Would you mind puttting that in laymans terms
    Thanks

  4. #34
    Retired Defense Industry Engineer jadnashua's Avatar
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    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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #35
    DIY Junior Member charlie p's Avatar
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    Now that I understood
    Thank You

  6. #36
    In the trades Dana's Avatar
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    Quote Originally Posted by charlie p View Post
    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)
    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
    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.

  7. #37
    DIY Junior Member charlie p's Avatar
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    Hey Dana
    An I=B=R calc would at least find the right ballpark, and 100K ain't it, guaranteed.
    Thats funnyYES 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

  8. #38
    Retired Defense Industry Engineer jadnashua's Avatar
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    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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #39
    In the trades Dana's Avatar
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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. :-) )

  10. #40
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Dana View Post
    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. :-) )

    Dana,

    You write some good stuff.

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

    Nice Work.
    Theory only works perfect in a vacuum.

    Cyber Security Protection for Windows C:\ > WWW.WinForce.Net

  11. #41
    In the trades Dana's Avatar
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    Thanks for the kind words Don.

    My freshman roommate back in the day told me that I had...

    "A mind like a steel... garbage can!"

    ...and needed to write an encylopedia of trivia.

    Guess I've yet to be cured of that, affliction eh? ;-)

  12. #42
    DIY Junior Member charlie p's Avatar
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    Thanks Dana , Jim
    I was to nervous about returning the155 and getting an 80k.Was actually going to go with the 105 just to be safe.
    After reading your last post I had NO FEAR of ordering the 80
    With the help the Internet and your knowledge I have placed my order for the 80k. And am confident in the choice. Should be here by Monday.
    THANK YOU SOOOO MUCH

  13. #43
    DIY Member Handymaner's Avatar
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    Quote Originally Posted by Edgeman View Post
    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."
    Dana and this board saved me from a 110 to 150k boiler when that was what everyone recommended. I installed a Lochinvar Knight 85K and it's worked terrifically this winter, and I live in Anchorage AK! I'm just working on tweaking my delta t to get the return water as low as possible for max condensing efficiency. It's already cut my bills by 50-70%!

    By the way, I don't know about the other brands but the Lochinvar has a max time for DHW heating-if something happens (as is suggested above) it automatically switches back to space heating after a certain amount of time, even if the DHW demand is not satisfied. It's one of the programmable parameters, if I recall the default setting is 30 min. So there are no worries of it getting "stuck" on DHW and the house going without heat.

  14. #44
    DIY Junior Member charlie p's Avatar
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    Dana,Jad and everyone else that shares their knowledge
    I just wanted to thank everyone for all the knowledge that you so willingly share.
    Without you I would have been running a WM ultra 155 instead of the 80.
    I'm quite happy with the results of the 80

    Heres the $$ bottom line
    OIL
    On 11-28-12 125 gallons of oil for $457
    On 1-4-2013 I took 208 gallons for $736
    to 3-13-2013 I took 100 gallons for $398
    By the time the new boiler was up and running the tank had may 10-20 gallons left in it
    As everyone knows, this has been a brutal cold winter.
    GAS
    11-29-13 I paid $64
    1-7-14 = $126
    1-24-14 + $159
    3-4-14 + $158

    With these numbers, This boiler will pay for itself in 2 years or less

    THANK YOU,THANK YOU,THANK YOU

  15. #45
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by charlie p View Post
    Dana,Jad and everyone else that shares their knowledge
    I just wanted to thank everyone for all the knowledge that you so willingly share.
    Without you I would have been running a WM ultra 155 instead of the 80.
    I'm quite happy with the results of the 80

    Heres the $$ bottom line
    OIL
    On 11-28-12 125 gallons of oil for $457
    On 1-4-2013 I took 208 gallons for $736
    to 3-13-2013 I took 100 gallons for $398
    By the time the new boiler was up and running the tank had may 10-20 gallons left in it
    As everyone knows, this has been a brutal cold winter.
    GAS
    11-29-13 I paid $64
    1-7-14 = $126
    1-24-14 + $159
    3-4-14 + $158

    With these numbers, This boiler will pay for itself in 2 years or less

    THANK YOU,THANK YOU,THANK YOU

    That is great.


    Enjoy.
    Theory only works perfect in a vacuum.

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