A Breath of Fresh Air: Appliances and Combustion Air
“Whan zephirus eek with his sweete breeth
Inspired hath in every holtand heath
Tendre croppes…” – The General Prologue of the Canterbury Tales, ll. 5-7.
[When Zephyrus (as well) with hissweet breath has brought forth life in the young crops of every wooded groveand open tract of land…][1]
The breath of life.
These lines can be found right at the outset of the General Prologue of the Canterbury Tales. Most folks have a shadowy, unpleasant memory of being subjected to this milestone of English literature from high school, but don’t worry, this is not an essay about the late fourteenth century or the nuances of Middle English poetry.
I do, however, want to stop for amoment on the word, inspire. Even if youhave little to no patience for the writing of Geoffrey Chaucer, it is importantto know that one of his lasting contributions to the English language was topopularize the addition of words from other languages. Chaucer introduced many Frenchand Latin terms that became part of our everyday speech because – you’re goingto have to trust me on this – his poetry was once very popular.
The lines above are one of if not the earliest recorded use of the word, inspire. The term comes from Latin and literally means to breathe into or upon. Think about it. When you expire, you breathe no more. Zephyrus or the West Wind breathing life into the young spring crops is one of many images, effective through their familiarity, that Chaucer uses in the General Prologue to establish the setting of the poem. The pilgrims in the poem set out on their journey at the zenith of spring, a sort of medieval Spring Break if you will. Spring, then as now, is associated with rebirth and new life after winter, and breathing, as you may have noticed, is fundamental to life.[2] Chaucer’s audience breathed, we breathe, fires breathe, and plants breathe. Nowadays, when something inspires, it gives life – usually in an intangible sense, but you get the point.
Houses breathe too. How air movesthrough a house is very important. Good airflow makes a comfortable, safeliving environment; poor airflow can lead to unhealthy or unsafe livingconditions.
Good airflow in an attic leavesthe space dry. Poor airflow can lead to a build-up of moisture that rusts metaland allows fungal growth to flourish in the insulation.
Air leakage around windows anddoors can make your timbers shiver, but sealing a house or room improperly can causeair to be drawn from unhealthy sources like crawlspaces.
How a house breathes is a primaryconcern of the architects and engineers who design them. The placement ofwalls, windows, doors, registers, vents, etc. all figure into what becomes afairly complex equation. Therefore, whenDIYers and contractors change the layout of a house, the way it breathes willinevitably be altered as well.
A short illustration will help.
The Case of the Rancid Room:
Not too long ago, I had thepleasure of investigating an absolutely atrocious smell coming from the boilerroom of an older house on a crawlspace. The boiler room was tucked away at theback of the original portion of the house. As for the terrible smell itself,the floor drain in the boiler room immediately became my primary suspect –floor drains have a long rap-sheet when it comes to unsavory smells. It iswell-known that when drain traps dry out, sewer gas can enter the house. Whatwould dry out the trap in the floor drain? Well, the only appliance in the roomwas the boiler. And what do boilers do? They make heat and they need air to breathe. It would be a bit surprising if justthe ambient heat from the boiler was drying out the floor drain, couldcombustion air be a factor? After a brief look around, I determined that theboiler’s source of combustion air included three connected but unventedcrawlspaces and a one inch gap under the door to the room.
My mind turned to themodifications had been made to the original structure. At some point a largeaddition had been put on the back of the house, adjacent to the boiler room.This addition likely, no, definitely changed the air supply for the boilerroom. The crime scene (the boiler room smelled terrible) began to come togetherin my mind.
Sure enough, when the boiler was running,the negative pressure in the room was enough to draw the door shut. Effectivelythe boiler was being made to breathe through a straw. The tiny one inch gap wasnot providing enough air to satisfy the boiler’s combustion air needs. As aresult, the draw on the floor drain combined with the heat of the boiler wasdrying out the trap and, desperate for any source of air, the boiler wasdrawing air from the sewer line outside.
Yuck.
The solution was to run aninsulated vent duct to the exterior of the house. As it turned out, the heatfrom the boiler itself was not enough to dry out the trap in the floor drain.And with a consistent source of fresh air, the boiler room stopped smellinglike a rest stop.
The Lesson:
Any appliance that has a flame, whether its fuel source is gas, propane, oil, or wood, needs air for combustion. Requirements vary by model but generally 30 cubic feet of combustion and dilution air (air that gets drawn into the chimney/exterior venting) is needed for every 1 cubic foot of gas. When appliances can’t breathe well, all sort of bad things happen: unhealthy levels of carbon dioxide, unburnt fuel, back-drafting, decreased efficiency, and, at least in one case, sickening levels of sewer gas drawn through the floor drain!
In the case recounted above, itwas the horrid smell in the boiler room that prompted investigation, but thiswas a unique case. If an appliance isn’t totallystarved for air, signs of a problem can be easily missed. What I see morefrequently are appliances that should last a decade or more failing prematurely.
You try exercising all day withsomeone’s hand over your mouth and see how long you last!
The good news is that it usuallyisn’t difficult for an HVAC contractor to remedy conditions such as these. Buteven before calling a contractor, here are a couple things homeowners can do touncover a combustion air problem.
The Steps:
- Identify which of your appliances need combustion / dilution air. The easy way to do this in utility rooms is to see what has a chimney: Furnaces, boilers, water heaters, and sometimes a stove – so, again, the ones with a flame.
- Figure out where the air for these appliances comes. Is it just the room in which they are located? Are there vents, a shortened door, or an exterior vent brining additional air into the room?
- Use this website to calculate how many cubic feet of air your appliances need and compare that number with the space from which your appliances are drawing air. The BTU rating for each appliance will be on its data plate. See below. Finally, if you have any doubts, call a qualified HVAC contractor to review the installation.
Suspect areas:
In the course of inspectinghomes, the two places I most frequently find combustion air problems are inbasements that were finished after a house was built and in the utility closetsof townhouses and condos.
Basements are often leftunfinished in new home construction. This could be a money-saving move or maybethe homebuyers want to do something cool and unique at a later date. Nevertheless,when a basement gets divided into smaller rooms, the appliances might suddenlybe getting only a fraction of the air they were when the basement was open andunfinished. Houses built between the late 80s and early 2000s are where I havefound this condition the most. (I’m looking at you, Meadow Branch andGreenwood.)
Home inspector’s tip: The ventsinto the utility area in your basement might be a bit unsightly, but don’tcover them with furniture or wall art. They serve an important function.
The utility rooms of condos andtownhouses often have a small exterior vents for gas-fired appliances to breathe.More than a few times, I have found that homeowners have unwittingly blockedthese vents not knowing what they were doing.
The Takeaway:
In an earlier blog, I wrote about the importance of going beyond just the realm of the visual when thinking about a house. Air is notoriously invisible, yet houses and many of the appliances in them rely on it as much as you do. Good air-flow is a cornerstone of health and safety; air-starved appliances can present real health hazards if they are back-drafting or spewing carbon monoxide into a house. They may also ruin your chances of having a nice dinner with friends if they are sucking sewer gas into your house!
With every passing year, theappliances we interact with become increasingly intricate, but they physics inwhich they are bound remain the same. A new, top-of-the-line gas range canrespond to oral instructions and tell you when it needs to be serviced. Thelatest furnaces and thermostats work together to achieve levels of comfort andefficiency beyond the imagination of our forbearers. But the flames thesefixtures enfold still need air just they always have. After all, “out of oldebokes, in good faith, Cometh al this newe science that men lere.” [“from oldbooks, in good faith, comes all this new science that people learn.”]– Parlement of Foules, ll. 24-25.
Sorry. I couldn’t help it.
- Joe
[1] Translating poetry intoprose is always problematic.
[2] Yes. I know there are someweird forms of single-cell life that don’t need use oxygen, but discussion ofthese didn’t come up a lot in the Middle Ages.
