Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Boiler replacement sizing help!!

Rob48xxRob48xx Member Posts: 21
Due to issues with existing boiler i am trying to get a good understanding of a replacement solution. I have received 6 quotes from 3 oil companies and 3 heating/plumbing companies and the size of the boiler is all over the place and im unsure which is accurately sized. My goal like any, is lowest cost while using as less oil as possible.

What i have:
1. Side Power vented, no chimney
2. New Yorker APH_790
3. Appears to be D.O.E. 120 MBH
4. No water heater as boiler provides domestic and heat
5. 112 linear ft of 7.5" baseboard forced hot water
6. 1300 sq ft split amongst 2 zones 1st and 2nd fl. Boiler in basement with no heat/zone
7. Rhode island weather with 4 people in house
8. Oil fuel with Beckett burner

What i am looking for is sizing of boiler to support:
1. High efficiency boiler supporting exisitng details above with direct vent kit.
2. Separate in direct hot water heater

I figure with the 112 ft of baseboard at 600 BTU per foot and some addition loss to be at 70,000 but i dont know what to add for the indirect.

Any idea of using this data what is more accurately sizing should be? I have quotes with 87,000 BTU up to 114,000 BTU.

Please help our solution is dying any day now.


  • Rob48xxRob48xx Member Posts: 21
    edited March 14
    Hi folks....

    I want to first say i am about 15 mins old to this forum so if i am posting in the wrong place or not doing something correctly i apologize.

    Ive been having a horrible problem with my existing New Yorker APH790 boiler. I have concluded after being 19 years old to replace it. We dont have a water heater for domestic both heat and hot water is from boiler.
    I decided to upgrade to a high efficiency oil boiler with a indirect but want to be sure its being sized correctly from the quotes i received. I decided to get 6 quotes (3) from heating/plumbing co and (3) from oil companies.
    They are all over the place in size and cost which has me very confused and unsure of what is accurate. The pricing ranged from $9500-$12500. Here is some details of what i hope will help size correctly.

    1. House built 2000
    2. insulated double pane windows
    3. Rhode island weather with 4 people in house.
    4. unfinshed basement where the boiler is located
    5. 112 linear ft of 7.5 inch hot water baseboard
    6. Oil boiler with no chimney, direct vent
    7. 1300 sq ft, 2 floors mostly carpet
    8. 2 zones 1st and 2nd floor no heat in basement
    9. Adding indirect 40 gal
    10 adding high efficiency oil boiler

    From my simpleton approach i took baseboard x 600 btu per foot and add some addition for heat loss and came up wirh like 70000 but i dont know what to add for a water heater we never have which seems to be a new 3rd zone.

    I got quotes with 80,000 up to 120,000 BTU so i dont know who is right. Its been a long process that is killimg me.

    Any help is greatly appreciated
  • Rob48xxRob48xx Member Posts: 21
    Rhode Island weather
    4 people live in the house
  • Rob48xxRob48xx Member Posts: 21
  • IronmanIronman Member Posts: 5,573
    500 btus per lineal foot is a more accurate number. So, your radiation is capable of about 55k btus. Why you you want a boiler capable of any higher output considering you only need that much on the coldest night of the year?

    Unless you have an unusually high domestic load, a 40 gal indirect would suffice.

    The indirect is given priority in the controls, so you DON'T add that to the sizing of the boiler.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,945
    Your 70,000 is correct for the amount of baseboard you have.

    A good contractor should do a heat loss but most wont.

    Do not add anything for domestic hot water. A 40 gallon indirect will usually do the average house with a couple of bathrooms and 3-4 people. If you have a whirlpool tub etc you will have to install something larger like a 50 gallon.

    With oil as a fuel the smallest oil boiler will do what you need, I would suggest something like a Weil McLain WGO. I would downfire it slightly with a smaller nozzle
  • HVACNUTHVACNUT Member Posts: 3,279
    None of the contractors performed a heat loss calculation? Well no return call for any of them.

    Where are you located?
    There's a "Click Here" to find a contractor in your area tab at the top of the page.

    The existing boiler is a steel dry base with a tankless coil. Probably the least efficient system you could have.

    Most here will steer you towards a cast iron 3 pass boiler with an indirect water heater, or an Energy Kinetics System 2000.

    The EK is a package. With the water heater. No extras needed. Direct sidewall (not power vent) venting is optional with the lower firing rates.

    With any other boiler, controls can be added or substituted to increase efficiency and funtion.

    Download the free Slant/Fin heat loss calculator and see for yourself what size you need.
  • Rob48xxRob48xx Member Posts: 21
    Thanks there a disadvantage to going with something larger like a viessmann vr33 as an example?
  • Rob48xxRob48xx Member Posts: 21
    HVCANUT, i am in RI and the only contractor that comes up seems to be a steam only contractor with the next one being almost 40 miles away not servicing my location.

    As for the heat loss, i was surprised none were done even after i asked how they determine the sizing however i did this with 6 different company's which is my concern. Example would be the viessmann vr22 quoted by one and the other a vr33. Why would they both be that off from each other. Attached is a product sheet as an example
  • Rob48xxRob48xx Member Posts: 21
    I included the water leak picture as that started only the last 5 or 6 days and i dont think is the cause but a result of the boiler cooling down and gaskets shrinking.
  • Jamie HallJamie Hall Member Posts: 12,719
    If wiggling the primary ignition box gets things going, the first thing I'd be looking at is all the wiring and the connections. Inside the box and out. Take the cover off, make sure all the connections (may be screws or spades or multi-plugs of various flavours) are tight. Make sure there are no broken wires, and that all of the have good insulation. Make sure particularly that the power supply and ground connections are good.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • HVACNUTHVACNUT Member Posts: 3,279
    edited March 15
    The 70K NET output on the VR22 matches the baseboard output at 180° so it's a no brainer, right? Wrong.
    At just under 54 BTU per sq ft, it's still grossly oversized. (Did you add the basement to your house sq ft? If it's not a crawl, add it.

    The domestic hot water does not come into account when sizing unless it exceeds the heat loss. Got 2 jacuzzi tubs and a commercial dishwasher?
    DHW can be made priority so when theres a demand the boiler will give it's full energy to replenish the tank.

    The sad thing is you'll be hard pressed to find an oil fired boiler small enough.

    In a nutshell, any manufacturers smallest oil fired boiler is more than enough.

    Depending on how far you want to go, adding a buffer tank, Outdoor Reset, piping and mixing design will offset that extra size. For a cost up front. You save on the back end.
    That's where the contractor needs to know their stuff. The Stooges could slap a boiler in, but to install it properly and get the boiler to produce the necessary output with the least amount of fuel consumption is the goal.

    And try to stay away from a power vent. Unless in the case of the EK Resolute, IMO. Direct venting is ok.
  • Erin Holohan HaskellErin Holohan Haskell Member, Moderator, Administrator Posts: 1,294
    @Rob48xx, welcome to Heating Help. We've merged all of your posts here. In the future, please post the same question in just one category. Thanks!
  • Rob48xxRob48xx Member Posts: 21
    HVACNUT...we have a standard dishwater, one standard type . I personally get the sense oversized because they want me to use more oil since i noticed the oil company quotes seem to oversized more than tje heating plumbing co. Will a oversized boiler, other than cost have that effect?
  • Rob48xxRob48xx Member Posts: 21
    > @Jamie Hall said:
    > If wiggling the primary ignition box gets things going, the first thing I'd be looking at is all the wiring and the connections. Inside the box and out. Take the cover off, make sure all the connections (may be screws or spades or multi-plugs of various flavours) are tight. Make sure there are no broken wires, and that all of the have good insulation. Make sure particularly that the power supply and ground connections are good.

    Thanks ill take a look
  • Rob48xxRob48xx Member Posts: 21
    > @Erin Holohan Haskell said:
    > @Rob48xx, welcome to Heating Help. We've merged all of your posts here. In the future, please post the same question in just one category. Thanks!

    Thank you. I figured 2 different topics, 2 different posts to avoid confusion on topic
  • SteamheadSteamhead Member Posts: 13,773
    @Rob48xx , if that "steam contractor" is closest to you, call them. If it's who I think it is, they should be able to take care of you. If not, they should be able to recommend someone.

    Do NOT hire anyone who does not do a heat-loss calculation.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • Rob48xxRob48xx Member Posts: 21
    > @HVACNUT said
    > At just under 54 BTU per sq ft, it's still grossly oversized. (Did you add the basement to your house sq ft? If it's not a crawl, add it

    There is no heat registers in the basement and was not included in my numbers
  • HVACNUTHVACNUT Member Posts: 3,279
    edited March 15
    The red button raises when it goes into safety lockout.
    If the button isn't raised, but still not firing, check those connections. But it's more likely faulty contacts in the primary. I used to see it a lot back in the twentieth century. Boy that was cool to write.

    Pretty simple to diagnose.
    Upgrade to a 15 second safety, interrupted ignition primary.

    Try to find a reputable contractor with whom you can get a maintenance agreement. Make sure they do a combustion analysis whenever the burner is serviced.

    The primary control issue alone isn't reason for replacement, but time is ticking so start saving. Some companies offer 0 or low interest loans if you agree to use their services and purchase fuel through them for X years.

    Edit: If the basement is part of the conditioned space, then it must be added to the calculation. Even if that space isn't heated.
  • Rob48xxRob48xx Member Posts: 21
    > @HVACNUT said

    Do i need to jump the T T on the new primary relay? I picked up a new honeywell R8184G4009?

    I have a Beckett burner, no water heater, a power vent and an aquastat
  • HVACNUTHVACNUT Member Posts: 3,279
    > @Rob48xx said:
    > > @HVACNUT said
    > Do i need to jump the T T on the new primary relay? I picked up a new honeywell R8184G4009?
    > I have a Beckett burner, no water heater, a power vent and an aquastat

    Return it. That control has been obsolete for eons.
  • Rob48xxRob48xx Member Posts: 21
    Its the only one i can get that Honeywell says is the replacement. I unfortunately also installed it before i seen your msg. Boiler powered right up and i didnt need to nudge the unit like i did before. However, seems like boiler wont shut off now and brought the water temp above the high limit of 180 to 210 before i got anxious and shutdown from the emergency switch. Ever hear of this? I connected the 3 wires on the new unit exactly as the oldand connected the cad wires to the FF terminals. Only difference is i jumped TT on the unit as i have the thermostats to the aquastat.
  • HVACNUTHVACNUT Member Posts: 3,279
    Black from the aquastat to Black on the primary.

    Orange from the motor and 1 Black from the ignition transformer to Orange on the primary.

    Whites from the aquastat, primary, motor, and the other black from the ignition transformer all spliced together.

    Jumping TT is fine.
  • Rob48xxRob48xx Member Posts: 21
    Hmmm...i just put the old unit back in and not shutting this thing is tryng to kill me. Lol
  • Rob48xxRob48xx Member Posts: 21
    I verified all the cabling and its correct. I wonder if the thing was over heating before and i didnt notice??? My hi is 180 so i would expect not to exceed that. Here is a pic of the aquastat settings 180 and 160 with a differential between 10 -15
  • HVACNUTHVACNUT Member Posts: 3,279
    Lower the aquastat to
    140 Hi
    120 Lo
    See if it cycles off and on.

    It could be a faulty gauge.

    The burner MUST shut off. Don't run it if the burner wont shut off.
  • Rob48xxRob48xx Member Posts: 21
    Thanks, I appreciate your replies.
    Yeah my fear is the boiler will keep running, over heating and busting as i noticed the pressure gauge is increasing when the temp gets high.

    Should i adjust these values as its running?
  • Rob48xxRob48xx Member Posts: 21
    Hmmm...interesting. i adjusted to 160 140 during cycle and it shut off as soon as i lowered the high value even though the temp was reading 210. I think you are right....seems like the gauge on the aquastat and what the temp is reading dont add up. Turned it back to 180 and boiler came on yet it was still reading almost 210. Will see qhen it calls again if it shuts off when it starts
  • HVACNUTHVACNUT Member Posts: 3,279
    edited March 17
    It's got to be verified.
    Could be a bad tridicator gauge. But it also be a plugged or faulty relief valve. Or its doing its job. Ruptured bladder in the extrol, bypassing auto feed. Hole in the tankless coil.

    Keep the temps low for now. 150- 130.

    In one of the pics you posted there's water on the floor. Is there a discharge pipe for the relief valve? The Back Flow Preventer has one going into the bucket.
  • Rob48xxRob48xx Member Posts: 21
    There was some water that came from the relief valve at a few times. What i think was happening was it was over heating either due to that gauge or the knobs on the aquastat causing the boiler to over heat and over pressurize and maybe was doing its job. Then after that happening daily for a few weeks developed a crack or leak in the tank and i was able to pull the case apart and see leak history in the tankless which explains why i didnt have that puddle until 3 weeks or more of problems.
  • Rob48xxRob48xx Member Posts: 21
    it's coming off and on now and seems to be working fine at the moment and I didn't need to nudge the primary control unit. I think maybe when I tried to replace the primary control unit and the boiler didn't shut off causing me to reinstall the old unit I may have inadvertently corrected a loose wire in the primary control unit fixing that issue but not the issue causing the high low temperature issue. I really appreciate all your help. For now I am going to still go with replacing the boiler but at least I have a temporary solution for now while i sort out the best boiler size 4 the house. I spoke with the oil company today and asked why they sized a boiler with the 122 net BTU and he still believes it's what's right for this house even though the basic measuring using using the linear feet of the baseboard heating or the square feet of the house comes up with 70,000 BTU's. without doing a heat loss calculation I don't know how he's able to determine that so granularly but I've asked him to scale the unit back to a smaller model one step down that has a nephew of 90000 BTU which seems closer size for this house.
  • HVACNUTHVACNUT Member Posts: 3,279
    If your talking about the Viessmann, then yes, demand the VR-22. Tell them you'd go even smaller if they made one.

    At 70K BTU net, the VR-22 gets you 54 BTU per sq ft in your 1300 sq ft home. You wouldn't need that if an arctic avalanche dropped on your house.
    And as discussed earlier, your baseboard can't put out more than that anyway at 180° SWT.
    Even after you add the basement (partial on your split, 6 to 7 ft below grade) the VR-22 is overkill.

    If your happy with the oil company for the installation other than the boiler size, use them over the others you had out, but maybe get estimates from 2 new companies. Preferably one that offers a full service oil agreement. If you go with an HVAC contractor, make sure they have qualified oil service techs.

    Do what you can now for efficiency. I know Viessmann offers their own operating control aquastat and outdoor reset. I'm not familiar with it. I only took their gas mod con classes when I was up there.

    Find out what burner will be installed. I prefer Riello but would lean towards the one that offers the lowest firing rate for the VR-22.
    Well, that's not true. If it were me I'd get the Riello anyway.

    Primary/Secondary piping will also aid in efficiency, boiler protection, and equal temperatures to the zones.

    As far as the primary, I guess its possible the removal, smacking around, reinstalling, realigned the contacts. Or knocked some carbon off.
    Don't return the new one until after you replace the boiler.
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!