A Breath of Fresh Air: Appliances and Combustion Air
“Whan zephirus eek with his sweete breeth
Inspired hath in every holt and heath
Tendre croppes…” – The General Prologue of the Canterbury Tales, ll. 5-7.
[When Zephyrus (as well) with his sweet breath has brought forth life in the young crops of every wooded grove and 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 a moment on the word, inspire. Even if you have little to no patience for the writing of Geoffrey Chaucer, it is important to know that one of his lasting contributions to the English language was to popularize the addition of words from other languages. Chaucer introduced many French and Latin terms that became part of our everyday speech because – you’re going to 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 moves through a house is very important. Good airflow makes a comfortable, safe living environment; poor airflow can lead to unhealthy or unsafe living conditions.
Good airflow in an attic leaves the space dry. Poor airflow can lead to a build-up of moisture that rusts metal and allows fungal growth to flourish in the insulation.
Air leakage around windows and doors can make your timbers shiver, but sealing a house or room improperly can cause air to be drawn from unhealthy sources like crawlspaces.
How a house breathes is a primary concern of the architects and engineers who design them. The placement of walls, windows, doors, registers, vents, etc. all figure into what becomes a fairly complex equation. Therefore, when DIYers and contractors change the layout of a house, the way it breathes will inevitably be altered as well.
A short illustration will help.
The Case of the Rancid Room:
Not too long ago, I had the pleasure of investigating an absolutely atrocious smell coming from the boiler room of an older house on a crawlspace. The boiler room was tucked away at the back 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 is well-known that when drain traps dry out, sewer gas can enter the house. What would dry out the trap in the floor drain? Well, the only appliance in the room was the boiler. And what do boilers do? They make heat and they need air to breathe. It would be a bit surprising if just the ambient heat from the boiler was drying out the floor drain, could combustion air be a factor? After a brief look around, I determined that the boiler’s source of combustion air included three connected but unvented crawlspaces and a one inch gap under the door to the room.
My mind turned to the modifications had been made to the original structure. At some point a large addition 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 boiler room. The crime scene (the boiler room smelled terrible) began to come together in my mind.
Sure enough, when the boiler was running, the negative pressure in the room was enough to draw the door shut. Effectively the boiler was being made to breathe through a straw. The tiny one inch gap was not providing enough air to satisfy the boiler’s combustion air needs. As a result, the draw on the floor drain combined with the heat of the boiler was drying out the trap and, desperate for any source of air, the boiler was drawing air from the sewer line outside.
Yuck.
The solution was to run an insulated vent duct to the exterior of the house. As it turned out, the heat from 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 smelling like 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, it was the horrid smell in the boiler room that prompted investigation, but this was a unique case. If an appliance isn’t totally starved for air, signs of a problem can be easily missed. What I see more frequently are appliances that should last a decade or more failing prematurely.
You try exercising all day with someone’s hand over your mouth and see how long you last!
The good news is that it usually isn’t difficult for an HVAC contractor to remedy conditions such as these. But even before calling a contractor, here are a couple things homeowners can do to uncover 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 inspecting homes, the two places I most frequently find combustion air problems are in basements that were finished after a house was built and in the utility closets of townhouses and condos.
Basements are often left unfinished in new home construction. This could be a money-saving move or maybe the homebuyers want to do something cool and unique at a later date. Nevertheless, when a basement gets divided into smaller rooms, the appliances might suddenly be getting only a fraction of the air they were when the basement was open and unfinished. Houses built between the late 80s and early 2000s are where I have found this condition the most. (I’m looking at you, Meadow Branch and Greenwood.)
Home inspector’s tip: The vents into the utility area in your basement might be a bit unsightly, but don’t cover them with furniture or wall art. They serve an important function.
The utility rooms of condos and townhouses often have a small exterior vents for gas-fired appliances to breathe. More than a few times, I have found that homeowners have unwittingly blocked these 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, the appliances we interact with become increasingly intricate, but they physics in which they are bound remain the same. A new, top-of-the-line gas range can respond to oral instructions and tell you when it needs to be serviced. The latest furnaces and thermostats work together to achieve levels of comfort and efficiency beyond the imagination of our forbearers. But the flames these fixtures enfold still need air just they always have. After all, “out of olde bokes, in good faith, Cometh al this newe science that men lere.” [“from old books, 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 into prose is always problematic.
[2] Yes. I know there are some weird forms of single-cell life that don’t need use oxygen, but discussion of these didn’t come up a lot in the Middle Ages.
