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Where should combustion air come from?

Jonathan_3
Jonathan_3 Member Posts: 1
Where should combustion air come from? My house has a 3 year old steam boiler (115,000 BTU, IIRC) and the combustion air is just sucked from the basement. The house is old, so I guess the make-up air comes in just about everywhere, but I am in the process of insulating and replacing windows, so presumably it is getting tighter.

Should I have a combustion air duct installed to the outside, similar to the one described here:
http://www.state.mn.us/mn/externalDocs/Combustion_Air_110802035809_CombustionAirO7-03.pdf

Comments

  • Constantin
    Constantin Member Posts: 3,796
    IIRC, in MA the answer is yes.

    Our landlord recently had to put in a new steam boiler when our downstairs neighbors went up in smoke. Part of the new boiler installation was a device that actively sucks air into the basement from the exterior whenever the boiler fires. Fairly useless when one considers the 2 gas water heaters + our boiler who do not trigger the fan still in the basement.

    Anyway, I'd take a look at whether your heating system could be converted to a sealed system, i.e. one that draws its air directly from the outside. That severly limits the possibility of CO or other nasties escaping into your basement.
  • Ken D.
    Ken D. Member Posts: 836
    Combustion air.

    Most units have devices to pipe in outdoor air as an option. Check it out.
  • Weezbo
    Weezbo Member Posts: 6,232
    if it is gas....if it is oil...

    makes little difference get the air from outside the building that way your indoor air quality will improve and maybe most likely, so will the burn of your appliances.
  • Nick_11
    Nick_11 Member Posts: 25
    Outside air duct

    for makeup will be safer and more comfortable. Our house and apartment in Minnesota are about 75 yrs old and both have boilers and gas hot water heaters. My theory is that without easily available outside makeup air, the inside air the boiler must pull eventually comes in from the outside anyway, but through the surrounding living space (around window frames,doors, you name it..) creating drafts on cold days. Drafts were so bad in our apartment last winter that our renter moved out (fled). Hence we're currently eliminating the 40 yr. old boiler / new water heater on the main floor and putting a new sealed combustion unit with indirect Hot water heater in the garage below.

    Outside makeup also reduces chance of carbon monoxide and flamables that might leak or spill. Also in Minny, fresh makeup air could possibly lead to frozen pipes and other headaches.

    Thats probably more than you wanted to know, but hope it helps...

    Nick
  • heretic
    heretic Member Posts: 159
    It depends

    How tight is tight? Really hard to know without a blower door test.
    How many other appliances are competing for intake air?
    Bathroom fans, range hood, dryer...

    Code gives guidance regarding minimum volume of boiler room and such. Makeup air is not always required by code, but looking for actual backdrafting under max structure depressurization is a better test.
  • R. Kalia
    R. Kalia Member Posts: 349
    drafts

    > Drafts

    > were so bad in our apartment last winter that our

    > renter moved out (fled). Hence we're currently

    > eliminating the 40 yr. old boiler / new water

    > heater on the main floor and putting a new sealed

    > combustion unit with indirect Hot water heater in


    You are trying to solve a major problem by making very expensive changes whose effects on air flow is extremely minor.

    If you have a leaky house, spend much less money to do a blower test, or if you have a strong window fan, use that to do an informal blower test and look for leaks (best done when it's cold outside to incoming air can be felt more easily).
  • Nick_11
    Nick_11 Member Posts: 25
    Blower Test

    tells me something I already know. Apartment is 75 years old and has 23 windows (80+% of exposed wall)It also sits above unheated garage. Its a classic looking structure but its construction has inherent drawbacks that limit the effectiveness of insulation and make it more expensive and difficult. It also sits above unheated garage. I also know with 60% increase in nat gas costs over past 2 yrs, that I need to replace boiler installed in 1964. Makes sense to me to get boiler and water heater out of living area (replacing it with stacked washer/dryer). You're right, installing new boiler is expensive, but do I need to add a blower test to that cost?
  • Nick_11
    Nick_11 Member Posts: 25
    Blower Test now...

    would tell me something I already know. Apartment is 75 years old and has 23 windows (80+% of exposed wall see attached pdf). It also sits alone on top of an unheated 3 stall garage. Boiler was installed in 1964. Its a classic building, but its construction has inherent weaknesses that limit the effectiveness of insulation and make it very expensive.

    Because I'm restoring it as much as possible myself, don't have $20-30,000 to replace all the windows (they've been reconditioned) and can use the existing boiler space for a stacked washer/dryer,it seems like a no-brainer to me to replace the old boiler (nat gas price up 60% in last 2 yrs) and put the new one downstairs with sealed combustion and indirect DWH.

    I'm also doing the boiler now because the place is vacant. Much of old heat return pipes go thru the attic and will be scrapped. Adding returns to Baseboard to minimize common piping in garage.

    With an old house, the story goes on and on. No silver bullets...

    I like your idea of blower test, but think I should spend the money on it after I've done the obvious.

    One last "also"; If I don't bite the bullet on this boiler issue now while I have the $$ earmarked, I don't want to think of what could possibly happen in the dead of next January....

    Nick
  • Nick_11
    Nick_11 Member Posts: 25
    RE: Drafts...Blower test

    Blower test now would tell me something I already know. Apartment is 75 years old and has 23 windows (80+% of exposed wall see attached pdf). It also sits alone on top of an unheated 3 stall garage. Boiler was installed in 1964. Its a classic building, but its construction has inherent weaknesses that limit the effectiveness of insulation and make it very expensive.

    Because I'm restoring it as much as possible myself, don't have $20-30,000 to replace all the windows (they've been reconditioned) and can use the existing boiler space for a stacked washer/dryer,it seems like a no-brainer to me to replace the old boiler (nat gas price up 60% in last 2 yrs) and put the new one downstairs with sealed combustion and indirect DWH.

    I'm also doing the boiler now because the place is vacant. Much of old heat return pipes go thru the attic and will be scrapped. Adding returns to Baseboard to minimize common piping in garage.

    With an old house, the story goes on and on. No silver bullets...

    I like your idea of blower test, but think I should spend the money on it after I've done the obvious.

    One last "also"; If I don't bite the bullet on this boiler issue now while I have the $$ earmarked, I don't want to think of what could possibly happen in the dead of next January....

    Nick



    Attachments: aptartment.pdf
  • Constantin
    Constantin Member Posts: 3,796
    Consider Insulation + Infiltration

    There are a lot of different means of getting the house perimeter tight, even if you have extant walls. Consider open-cell polyurethane insulation. It's not quite a vapor barrier, but pretty close, and can be installed in extant walls without having to pull them down. That should cut down on the whistling past the windows. Budget about $0.90 per boardfoot for in-wall and $0.30 for open cavity professional installations. YMMV, of course. 1 boardfoot = 12"x12"x1", i.e. 144 cubic inches.

    As for the windows, I wouldn't waste my $$$ on new ones if the old ones have been reconditioned well. Instead, I'd install Harvey Tru-Channel storms. Not only do they cost much less than a new window, they also offer an infiltration of 1/10th of what is required. With a good storm, the thermal properties is not much different from a $$$ thermopane, yet the system does not rely on a vacuum or noble gas to stay put. KISS.

    Between the in-wall and window infiltration improvement, the comfort levels inside that apartment will probably improve a lot. Only then would I resort to buying a new boiler, once the load has been reduced and I can reap my just rewards for having made the envelope tighter.
  • Weezbo
    Weezbo Member Posts: 6,232
    constantine jus gave you a good answer

    insulation around windows and doors is well worth the investment .the spray foam that is made for windows is right on these days. next thing if you little sparse on dineros polyethelyene sheathing when applied from out side over the windows help cut drafts and actually provide a kind of hollow that acts like a full pane of glass.
  • Big Ed
    Big Ed Member Posts: 1,117
    Air intake

    You need 1" opening per 1000 btu so you will need 115 square inch of opening to satisfy your boiler's combustion needs..
  • Nick_11
    Nick_11 Member Posts: 25
    KISS in an Old House?


    Improving an old house is not simple stuff. KISS usually only sounds good and a lot of work done that way ends up as temperary CRAP. Plastic sheets over windows and stuff like that.

    What is easy to keep simple, is to replace the 40 year old boiler and water heater on the living floor with a sealed unit downstairs in the garage. Last winter the tenant got a FREE blower test every time they lit up. Dubious chimney too.
    Boiler put in back in '64 when fuel was cheap and very little planning was done on the design and distribution of the heating pipes. Many of the returns are in the attic. Talk about wasted heat, not to mention all the bypasses.

    Draft is still the big problem, but in an old structure, you have to make painstaking, expensive little improvements in a lot of areas. There is no holy grail here. But the Volcano is probably the largest improvement I could make And I want to do it now while I have time to plan it, it's spring and the place is vacant. Storms are in excellent condition I spent all last summer, sanded, reglazed, primed with shellac, top coated. Had 2 bids for poly spray (about $1100). Both came out and looked at the place and said walls had to be open. Walls are 1920's beadboard, great shape, lots of character, so it'll take more time and effort to remove, spray and replace. You gotta really love old homes... But watch out if you KISS in one, you'll pay.

    Nick
  • Weezbo
    Weezbo Member Posts: 6,232
    Sold! :)

    get the boiler and water maker in the garage lose pipe returns through the attic:) no wonder it has been eating the probverbial breakfast! I would still bring in outside air to the appliance.and i honestly never been that keen on single pane windows... however insulation around them with the new form stuff is a tad more of a savings than the investment in time and materials to apply.insulation in the "Lid "is worth E V E R Y penny.good luck:)
  • Constantin
    Constantin Member Posts: 3,796
    Surprised!

    I'm surprised that your local foamers won't touch the closed walls. I've had several quotes from foam installers who'll install foam in-wall... from the exterior or the interior. If your area does not have sophisticated installers (in-wall typically requires an IR camera to verify fill), then I guess your approach of upgrading the heating system is the better one.

    I'm still going with both forms of insulating walls, but I'm aided by the fact that I have internally-unobstructed joist cavities on every floor. That makes the renewal of infrastructure easier (rip out the walls in those location) while preserving the plaster in other areas (because no one is going to do plaster like that again, blueboard is only close). I'm even having the installer install different foams in different locations to reflect the thermal loads. I.e. Mansard Roof/Walls will get closed cell foam (R-6/inch) while other walls will do with Icenyne (R3.7/inch).

    What makes me scratch my head a bit is how come you need new windows when the extant storms are in good shape. Where is all the wind coming through then? Or are you simply losing a lot of heat to the garage space below which isn't as well insulated?

    At the very least get the attic and the piping in it well-insulated. Fiberglass is bad at stopping drafts and one thing you can do yourself is use PU foam to seal all attic penetrations, then reuse the extant insulation.

    Going with a modern sealed combustion appliance is only going to help. However, without insulation and infiltration protection your next tenant may also take a hike (at least I thought it was your tenant, apologies if I'm confused as usual).
  • Nick_11
    Nick_11 Member Posts: 25
    Foam

    Thanks for your comment:
    "I've had several quotes from foam installers who'll install foam in-wall... from the exterior or the interior"

    Both contractors came to the apartment and said they needed open walls. Wouldn't do in-wall. Said foam wasn't designed to be applied that way and they couldn't guarantee coverage of all seams and leaks. Maybe they usually only work with new construction... We don't have the near the abundance of the really great, really old homes here in MPLS/STP that you guys have in the east. There aren't as many people who have experience with them.

    I'll call some other contractors to see if any will do in-wall and if they use cameras in their installation.

    Also, I Like my old inside windows, made out of some kind of mahagany colored? or hardwood, with original brass hardware - Wouldn't (and can't afford)to get rid of them. They are in ok shape, glazed etc.. They need refinishing and alot of weather stripping. Sealed everything for tenant last fall. Used a peal-off temperary weather calk from DEP around inside of storms and windows and applied 3M window kits. Alot of work plus about $100 expense, and tenant was still cold.

    You're right on the garage problem. Used the academic version of Seiganthaler Heat load analyser. Unheated, poorly insulated garage would use about 23,000 btu's if I remember correctly. lots of infiltration. Plan to replace garage door with R-19 insulated door and put polyisocyanurate foil faced sheathing on the walls. Looking into Dow Chem makes a product called Super-Tuff and one called Thermax that doesn't require a thermal barrier. 2x12 headers above plaster ceiling in garage are empty. Got one bid to hose some sort of insulation giving an R-44. He wants $1,800. I'll need other quotes there too. I have till next fall on that one.

    Thanks again for your input.

    Nick
  • nb_3
    nb_3 Member Posts: 3
    2 ?s

    if you have a duct for outside combustion air, is there any downside to bringing in supercold air say on a zero degree day right to the burner?

    if you just use basement air, is there a beneficial effect in that downward air draw will offset stack effect of unequal vertical heat stratification in the house?
  • Weezbo
    Weezbo Member Posts: 6,232
    0 degree air...

    0 degrre air is not likely to be a problem - 60 that basically requires some definite pre heat or Mixed air on the supply side on your combustion air. - 30 is where i kinda see some hassel beginning to evolve....
  • ScottMP
    ScottMP Member Posts: 5,884
    Actually in Mass..

    Most of the combustion air comes from Teddy Kennedy !

    Ohhhhhhh , I am good, thanks I'll be here all night.

    Tip your waitress.

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Weezbo
    Weezbo Member Posts: 6,232
    its 4 a.m. here :) milne have you any experience with

    triangle tube delta phase 111 ,(Oil fired tank in tank) ? i was intereseted in whether there is a conical insulator piece for their retention burner reillo burners in particular. rather than start a new thread and as it has something to do with combustion ...i thought thta i'd ask..
  • jackchips_2
    jackchips_2 Member Posts: 1,338
    To bad

    Dave Letterman has a long term contract, Scott.

    I can hear it now Heeeeeeeeeeeeeeeerrrrrrrrrrrrssssssss, Scott.
This discussion has been closed.