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computing air-volume : is "boiler room" big enough?

timo888timo888 Member Posts: 137
It's my understanding from reading on the web (please correct me if I'm wrong) that a 100,000 btu oil burner would require a boiler room 5000 cu ft or greater in order to have enough ambient combustion air to make sure none was being sucked back down the flue. Can the upstairs living area be added to the volume? Or is the computation limited to the specific room in which the boiler is located?


  • Robert O'BrienRobert O'Brien Member Posts: 2,930
    It takes

    1600 cu/ft to burn one gallon of oil with no excess air,most burners need at least 25 % excess air and some much more. Why not make it sealed combustion and bring combustion air directly into burner? It will cut way down on air infiltration,saving $ and increasing comfort as well as eliminating all combustion air volume/quality concerns
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  • EddieGEddieG Member Posts: 150

    I agree with Bob. Anytime you can use outside air, it's a plus. I have found anytime that I'm in doubt about combustion air, outside air is the correct answer. Especially with today's construction practices. Even in older homes people are looking for ways to seal them up. So what might be enough air today, might not be enough tomorrow.
  • timo888timo888 Member Posts: 137
    edited April 2011
    nominal versus actual when computing

    I googled and found how many BTUs a gallon of oil will yield, and got 115,000 actual and 138,000 nominal.

    My unit (already in place) is a 98000 BTU Buderus Logano with a Riello 40 F3. If I understand correctly, to get the unit's nominal fuel-per-hour consumption rate, we divide 98000 by 138000, which yields .71 gallons-per-hour.

    If I understand Robert's answer, I would multiply 1600 cu ft by .71 to get the minimum air-volume requirement for my unit: 1600 * .71 = 1136 cu ft.

    Or have I misunderstood?
  • Robert O'BrienRobert O'Brien Member Posts: 2,930
    Combustion air

    If you use 500 gals of oil /year that's 1,000,000 cubic feet of air per year sent up the chimney by the burner fan. Would you rather take that 1 million from your home or from the outside?
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  • timo888timo888 Member Posts: 137
    boiler room big enough (without fresh-air vent)

    Robert, thanks for the link. It gives advice on how to calculate vent-opening size in square inches. It will come in handy. But I'm not at that point yet. Now I'm trying to figure out if we're in violation of code in terms of size of basement given the BTU rating of the appliance.

    There were a number of cut corners in the installation: in the electrical wiring (ungrounded connections, no emergency shutoff switch at top of stairs), in the plumbing (no backflow prevention valve), in the flue venting (unnecessary 90-degree elbow), and some other things we're still looking into.
  • Tjernlund

    makes an "Inforcer" for combustion air makeup & it dont look like rocket science
  • timo888timo888 Member Posts: 137
    edited April 2011

    If I could find a small residential version, something like the In-Forcer would be interesting. These In-Forcers seem designed as a substitute for outside air, and start at 150000 BTU,   but all I may need to do is augment existing air volume.

    Thanks for the company name.
  • edited April 2011

    i figure~ 1cubic foot of air to burn 100 btu of oil or gas. then get the right fan for CFM & run it in conjunction with the burner so that when the burner burns the fan blows into the room from outdoor. IDEALLY the inhausting fan/blower blows into a bucket on the floor of the room & this bucket is a cold place 4 sodapop?

    I think the upstars can be included in room volume requirements so long as theres free airflow between the stories BUT I think NON-AIRTIGHT CONSTRUCTION is specified
  • edited April 2011

    ~ 20cfm will work for 100k BTU so an inhausting blower in conjunction with the burnergun would work? a cheapo bath exhaust fan blows ~ twice that much.

    Possible scenario is that the burner comes on as the bath & kitchen vents are running & the house experiences excessive vacumn & that might result in backdrafting without the inhausting fan
  • edited April 2011
    conceptual glitch

    is that if the house is too tight to allow proper air exchange, the vacumn created by the furnace & exhausting vents HELPS by air infiltration. The air xchange proposal aint about furnace having enough air as it is about BREATHING NON-STALE AIR into the lungs.

    The heatloss due to air infiltration thru house leaks is 720/100,000 BTU or pretty insignificant when its 20*f outside & 70*f inside? AN UNDERSIZED,TIGHT BOILER ROOM NEEDS COMBUSTION AIR FROM OUTDOOR & i THINK 20CFM WILL DO [any extra air is inefficient?] for a 100k burner but ask FC to make sure
  • icesailoricesailor Member Posts: 7,265
    Combustion air:

    You have a Riello burner. Install the outside air box and take your combustion air from outside and eliminate the largest part of your problem.

    At my last MA PHCC CEU, on the 3 hour gas part, at least an hour was devoted to make-up air for gas appliances. I have always pondered the question of wood louvers and how they were rated. I and others are quite wrong. A 10"x10" wood louvre isn't 100 sq. Inches. It's a lot less because of the wood. What you calculate may be a lot less. Outside air boots on a burner will close the factor a lot. I use them whenever I can. And this tightening up of houses puts a serious restriction on make-up air.
  • SteamheadSteamhead Member Posts: 11,322
    That's backwards

    because if a vacuum forms, the exhaust gases can't get up the chimney or out the sidewall vent. They'll go into the house instead, where they will attract lawyers.

    Any mechanical combustion air intake system must have an interlock that will not allow the burner to start until the fresh air flow is proven. Tjernlund uses their UC-1 relay system and a fan prover switch to do this, not sure how Field does theirs.
    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.
  • edited April 2011
    simplify & assume

    the burner is in a properly sized space which has iinadequate fresh air for breathing per 1/2 air exchange/hr. Without inforcer, the burner requires ~ 20cfm for 100KBTU/hr= 1200 cbic feet of added air/hr. exchange to the underventilated space. The burner pulls air from the space & induces air infiltration from outdoor from where the walls leak.
  • icesailoricesailor Member Posts: 7,265

    *.ass out of  U and Me

    The burner (air pump) fan will lower the the atmospheric pressure inside the house in relation to the outside, causing infiltration of the outside air. The outside higher pressure will find the easiest way to equalize itself. If it is easier to come down a chimney flue, it will do it in a NY moment.

    Flowing air has less pressure than static air. That' s why all those houses blow up in tornados and hurricanes. The inside pressure helps blow them up being higher than the outside and then the force of the wind finishes them off.
  • barometric damper would close?

    buoyancy + height of chimney establishes the draft

    most homes dont have inhausting blowers to assist with combustion air

    some call it heatloss due to infiltration, i call it proper breathing air
  • Jean-David BeyerJean-David Beyer Member Posts: 2,530
    why will my iceboat go 40 MPH in 8 knots of wind?

    and why can it sail heading almost straight into the wind?
  • icesailoricesailor Member Posts: 7,265
    Boiler Rooms:

    Are you asking  me?

    I was asking the question.
  • edited May 2011
    dunno if house is too tight

    but unless its perfectly tight its gonna exfiltrate air from fans & furnace. If all 3 can exhaust without affecting each other, the fresh air requirement will be assisted by leaks in the walls & the rule is 1/2 air exchange/hr as so stated? The glitch u fail to understand is that the tighter the house is, the more it needs mechanical ventilation . If the inforcer is installed near the boiler, it'll cancel the ventilating of the running boiler especially if the boiler pulled its combustion air from an upstair infiltration= the Inforcer should be located @ the opposite end of the house so that the breathing air gets efficiently exchanged
  • Jean-David BeyerJean-David Beyer Member Posts: 2,530

    No, I was not asking you, icesailor. I am certain you know the answer. I know also, if the reason is the same as why a water sailboat can do it, and I am pretty sure it is.

    I used to sail a Laser, and a former neighbor used to race an iceboat on the Navesink river about 2 miles from here until global warming set in and that river seldom freezes anymore. I have been here since 1976, and it froze only once. He had to race elsewhere, and he no longer lives here. His boat was pretty amazing. It uses more of everyting than my boat did, and uses steel (probably stainless) where mine used nylon and dacron for the lines. I think he said his would go 100 miles an hour under certain conditions, but I may be remembering incorrectly.
  • put it on the table man!

    hint= pressure differential + analysis of vector forces?
  • Jean-David BeyerJean-David Beyer Member Posts: 2,530
    Do not neglect airfoil

    The shape of the sail is normally not flat; it is an airfoil so additional vectors need to be considered. So pressure differential is a dynamic function. The pressure differential is a function of the shape of the sail, and the shape of the sail is, among other things, a function of the pressure differential. Any experienced sailor deals with this intuitively. No time to solve differential equations in real time using manual methods. Just as fate favors the prepared mind, so intuition is favored by experience wisely considered.
  • do u own a bidet?

    & why not?
  • timo888timo888 Member Posts: 137
    location of fan-in-a-can or comparable

    @pook: I do not understand this logic flow if your "inforcer" is a synonym for "fan-in-a-can":

    "... If the inforcer is installed near the boiler, it'll cancel the ventilating of the running boiler especially if the boiler pulled its combustion air from an upstair infiltration= the Inforcer should be located @ the opposite end of the house so that the breathing air gets efficiently exchanged..."

    What do you mean by "cancel the ventilation"?

  • Jean-David BeyerJean-David Beyer Member Posts: 2,530
    edited May 2011
    do u own a bidet? & why not?

    Presumptuous, aren't we? Of course I own one. I have to wash my socks and underwear somewhere, do I not? And if I left "it" on the table, I would have to wash that there too.

    Donations net needed.
  • edited May 2011
    absurd but true

    consider a perfectly tight house traiier & the furnace is @ 1 end & needs air 4combustion....put the inforcer @ the opposite end of the trailer & the airflow effectively replaces room air so to meet the rule for breathing. If the inforcer is located near the furnace, it wont wash thru the room air for breathing purpose as well. Actually a proper size hole would do the trick but it would have to open only when the furnace is firing= 2 factors

    1-furnace needs combustion air

    2-EPA sez u need fresh air per rule 1/2vax/hr

    just posted my fone # which involves no charge xcept what it costs the other end. feel free to call but wait till the machine identifies the caller so i know who it is....vvv

    inforcer & cancan are the same ithink= theyre inhausting vs exhausting like the furnace & bathvent
  • timo888timo888 Member Posts: 137
    edited May 2011
    undersized make-up fan

    I think you'd want the make-up air for combustion to mingle with ambient air in the boiler room so it isn't too cold when it gets sucked into the burner. Placing the fan-in-a-can some distance from the burner would therefore be good. However, if the burner is still drawing air down (or in) from the upstairs (or adjacent) living quarters even when the make-up air fan is pulling in air from the outdoors, the make-up fan is probably undersized, no? That's my layman's intuitive feeling anyway. You'd be using living-room-temperature air for combustion, which would be somewhat wasteful of fuel.
  • edited May 2011

    but u may need freshened air 2BREATHE/EPA depending on how tight the house is & the unassisted boilergun helps ventilate the breathing air if the house aint 2 tight. I just read the stuff & do the math/logic
  • timo888timo888 Member Posts: 137
    air quality of living quarters

    But air for breathing and air for combustion can be handled separately. I wouldn't want my fan in a can to do anything more than provide adequate air for combustion, even if the boiler room were completely sealed off from the rest of the house. You want to make it so the burner has zero effect on the air quality in the living quarters. Again, my layman's perspective.
  • sealed boiler room

    u def want the fancan PROPERLY COORDINATED WITH THE BURNER= IF SEALED BOILER RM HAS A 30CFM FANCAN INHAUSTING & THE BURNER TAKES 20CFM the room will pressurize & the result is?
  • timo888timo888 Member Posts: 137
    too much of a good thing


    My burner needs X amount of air. But my fan-in-a-can is oversized and so I'm giving it X + 30%. What happens?

    Layman cogitating.... {smoke pouring out of his ears fills the room ... }

    Possible answers:

    A) The overpressurized boiler room will keep the damper shut. The flue would go into overdrive and suck the excess air out of the boiler room, burner burning too hot, wasting fuel.

    B) Excess fresh cold air from outdoors will be pushed into the living quarters if the boiler room is not hermetically sealed off.

    C) All of the above.

    I choose C.

    Begging for mercy,

    Yours truly.
  • + vs - pressure

    its created a + pressure environment. A simple question would be= DOES THE BARODAMPER RQUIRE RETUNING AFTER THE FANCAN IS INSTALLED. i'd guess not because burner & baro are similarly affected by the pressure

    With a + pressure room the total inside is pressurized & where the walls once infiltrated they now might exfiltrate moreso. Pushing warm inside air carries humidity which condenses when the dewpoint is hit & under proper conditions mold can result . I prefer infiltration where the cold dry air comes in thru the cracks & tends to dry the area.

    Simply I'd close windows doors tight on a warm low wind day. Turn on every exhausting vent wwwith a non running boiler & then stick a piece of lit incense in the barodamper so to see which way the smoke is going. These conditions create the best conditions to see if the boiler will downdraft. This test is assumed by me so I await further comments from others. I'm curious also if new house construction for non-directvent burners requires fancan
  • icesailoricesailor Member Posts: 7,265

    Your circular logic is stunning.

    And potentially deadly.
  • Charlie from wmassCharlie from wmass Member Posts: 3,911
    some people think this is a game

    Felix is not the person I would have working on my system for sure.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • nothing like

    responding with substantive statements! This useless clutter reveals either cluelessness or megalomanic sollipsism. Again i'm attacked & the topic is avoided, why? If its dangerous, explain why/how cause i love to learn.
  • icesailoricesailor Member Posts: 7,265

    You're a lot smarter than anyone here. Explain it to us using words that some of us here can understand.
  • why?

    my last post sez nothing about the topic at hand =BS. My main concern is communicating with the OP, which seems ok, but beyond -if my ideas are wrong , I wanna know SPECIFICALLY so I can learn.
  • Jean-David BeyerJean-David Beyer Member Posts: 2,530
    If you really want to learn ...

    ... about the subject matter usually discussed here, consider reading some of the books available here.

    1.) (for hydronics):

    2.) (for steam):

    Other books available here:

    would go a long way.
  • cant find

    the book on sailing
  • Jean-David BeyerJean-David Beyer Member Posts: 2,530
    cant find the book on sailing

    google is your friend.
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