(A louvered door has horizontal slats for venting.) Visit our updated, This website requires certain cookies to work and uses other cookies to help you have the best experience. This is called a direct vent furnace. We deliver the best home inspections in your neighborhood. So each opening can be 13 inches by 13 inches square. Imagine putting a straw into an empty plastic soda bottle. This post deals with this type of furnace. of the appliances. The most common solution is to get combustion air from the rest of the house. Thats a pretty big room, and there are an awful lot of gas appliances stuffed into small spaces that just dont meet this requirement. Copyright 2022. That would not be a good thing as critters and birds could come into the room. I was giving a price to install a "air in a can" for combustion air when the inspector showed up. Your email address will not be published. of fuel burning components. Although the journeyman was wrong in his decision to break the glass without the owners permission, he instilled in me the importance of checking the combustion air openings on every service call. We deliver the best home inspections in your neighborhood.Our reputation is built on decades of honesty, integrity and excellent service to customers during one of their most important life decisions buying or selling a home. Let us assume we have a 40 gal., 40,000-Btu/hr. If the boiler room has an exhaust fan, it could adversely affect the venting of the flue gases. Probably the most important detail to keep in mind is that its never acceptable to get combustion air from a bedroom. hole in the wall, we will have a 100-sq.-in. opening. So the room needs to have a volume of 120 x 50, or at least 6,000 ft3. 240,000 total Btu/hr. Exhaust fans in boiler rooms can pull the flue gases from the burner into the main building. If you dont seal up the top around the straw then plenty of air can get back into the bottle to make up for all the air youre sucking out. Perhaps beenthere knows the reason for one high and one low. Make sure your boiler can breathe and stay safe. Why My Laminate Floor Flexes When Walked On, Do You Have to Use Rinse Aid in a Bosch Dishwasher | Pros Cons | How to Bypass, Where Must GFCI Outlets Be Installed? The following are some rules of thumb on free area for other combustion air openings: If you opt to use a fan for mechanical ventilation, you will need 1 CFM for every 2,400 Btu/hr. Xcels concern, obviously, was a safety issue that if venting was not properly maintained, indoor carbon monoxide levels may increase due to inadequate combustion and venting of gases. It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". On the other hand, standard efficiency furnaces typically have a metal flue, and they get their combustion air from inside the house. Mechanical fan. ft. of volume per 1,000 Btu/hr. This article was originally titled Can the boiler breathe? in the September 2016 print edition of PM Engineer. He can be reached at 412/343-4110 or ray@fireiceheat.com. Ray writes a monthly newsletter on commercial boilers. if some idiot took out the air intake for the furnace they might do anything just to finish the basement. Explained, What to Do After You Fill Your Pool With Water. By closing this message or continuing to use our site, you agree to the use of cookies. If the volume of the space is less than 50 cubic feet per 1,000 BTU/hr of total input for the gas appliances then its a confined space and its too small for safe operation of the gas appliances. In general, ventilated attics and ventilated crawl spaces are considered equivalent to the outdoors. Without oxygen the candle cant burn. Its just like the plastic soda bottle with a straw. We have to put two openings in the wall, one starting within 12 inches of the ceiling and one starting within 12 inches of the floor. But if the air pressure in the furnace room is lower than the air pressure outside then those flue gases can be sucked back into the house instead. So the flue gases cant rise up and out of the house, because they are being pulled back into the house by the drop in pressure. The opening must be in the upper 12 inches of the appliance space and it must have a net free area of at least 1 in2 for each 3,000 BTU/hr of appliance input. Then you calculate the volume of the appliance space. instead of 100 in. Each opening has to have a net free area of 120 in2, which meets the requirement of 1 in2 for each 1,000 BTU/hr. Figure 4: Two permanent openings must be sized and located correctly. by 10-in. If you simultaneously seal up the top around the straw then you can suck the air out and the bottle will even collapse because the air pressure inside is so much lower. equals 60-in. A single opening in the room is OK if it connects to the exterior or a properly ventilated attic. Each of the two openings needs to be at least 1 in2 for each 1,000 BTU/hr of input of all the gas appliances combined, but each opening must be at least 100 in2. W.C. can pull the flue gases from an atmospheric burner or pilot. The size of the ventilation openings we need is a fairly straight forward problem, because requirements for combustion air are specific, and they are uniform across all the codes and manufacturers requirements that Ive ever seen. Figure 1. WhatXcel Energydidnt mention specifically, but implied in its warning to consumers, isexteriorvents are also commonly obstructed with leaves, plastic bags, birds nests and lint. If the room is smaller than this then its a confined space and is too small to be safe. Indoor air. If we provide plenty of air to the room then the air pressure in the room wont drop and the furnace will be able to send the flue gases out of the house. This is done simply by putting vent openings in the furnace room to connect it to other rooms in the rest of the house and allow air to get in. Let me make sure I'm being clear. per each opening. In this post well discuss combustion air, including what happens if we dont have enough and what the requirements are for enough.. If we open a 10-in. Thats easy: we provide lots of combustion air to the gas appliances. input of gas burning appliances in the room. Right, that is the other option we've been considering, but there are reasons we don't want to go that direction. is the exhaust vent still there? The air that your gas furnace (and water heater, and boiler) needs in order to burn safely is called combustion air. They need oxygen to burn, and they get that oxygen from the air. Figure 3. Im sure that weve all seen the elementary school experiment where theres a lighted candle inside a jar, and a lid is put on. water heater and a 200,000 Btu/hr. So we install a metal louver with a screen in the opening. By visiting this website, certain cookies have already been set, which you may delete and block. The original high/low vents attached the basement to the living room of the house. I have found them blocked by grass clippings, old newspapers and plastic shopping bags. h4 If the same system as above is using indoor combustion air instead of outside air, the following is the size room we would need. Or 189, or even 53.33. Just at that time, the owner walked into the room. You also will need an interlock to verify the fan is operating before the boiler or water heater starts. Next Modern Home | All Rights ReservedHomePrivacy PolicyAbout UsContact Us. each. I've done a lot of searching and haven't seen anything describing why they're required. Ray Wohlfarth is the author of Lessons Learned in a Boiler Room: A common-sense approach to servicing and installing commercial boilers.In his spare time, he is president of Fire & Ice in Pittsburgh. Enter Our Dog Days of Summer BBQ Giveaway Now! Figure 1: The gas appliances are pulling air out of the house for combustion, and sending those flue gases out of the house. This is called back drafting. endstream endobj 401 0 obj <>stream All Rights Reserved BNP Media. why you sometimes need high & low air supply vents. And lets say that we know the appliance room is too small. Combustion Air (1) Air that is supplied to combustion appliances to be used in the combustion of fuels and the process of venting combustion gases. boiler for a total of 240,000 Btu/hr. What Happens if Fireplace Flue Is Closed. Went to look at a job today. I assume that the furnace has it's own air supply intake (again we haven't closed on the home so I don't have regular access to check these things). Although ventilated crawl spaces are a bad idea (but thats a topic for another post). divided by 1,000 equals 240. If theres not enough air, then theres not enough oxygen and bad things will happen. So if the openings will have a metal grill we need to allow for that, so each opening needs to have a total area of 120/0.75, or 160 in2. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! (A BTU is a British Thermal Unit, and is a standard measure of the energy contained in natural gas.) Most high efficiency furnaces get their combustion air directly from the outside. in. Horizontal duct opening. For example, say your furnace and water heater are in a room together. If you dont want to or cant use a louvered door, here are your other options. When your furnace is running its pulling combustion air out of the room and through the flame, and then exhausting it out of the house through the flue. If the openings connect directly to the outside or connect to the outside through vertical ducts then each opening must have a net free area of at least 1 in2 for each 4,000 BTU/hr of appliance input. The minimum dimension of each opening is 3 inches. The first thing to determine is if the room with the gas appliance is big enough to supply all the combustion air. When posting in certain forums, knowing your location will help others give better feedback/advice/solutions to your questions. This will work as long as the rooms combine to meet the 50 ft3 per 1,000 BTU/hr input requirement. Be sure to contact a qualified contractor when providing combustion air. After completing his calculations, he announced the existing grill was too small for the boiler room. This could allow the dangerous flue gases into the building. 8Uc?W;ttQN. A recent fast moving snowstorm expected to bring heavy accumulation of snowfall hadXCEL Energy(natural gas supplier) warning radio listeners of making sureexteriorvents were not blocked by snow buildup. It was the first and only time I was ordered to leave a jobsite. So what to do if the appliance space is too small? There are several other options for getting combustion air, including air from a crawl space, an attic, and from the outside. by 10-in. Please click here to continue without javascript.. This website requires certain cookies to work and uses other cookies to help you have the best experience. That opening would be large enough for 300,000 Btu/hr. But 3 inches is our minimum dimension, so the opening couldnt be any more squished than that. All fossil fuel burning appliances need ample air intake and draft to complete the combustion process in a safe and efficient manner. There are other details as well, but this gives the basic information. Please take a moment and locate the vents that supply your gas appliances making sure they are freely open, unobstructed, and able to do the job they were designed to do. I like to check the outside of the louvers to make sure they are clean and unobstructed. If it is not available, I use a factor of 75% free area for metal louvers so our free area of the 10-in. This is the best and most efficient way to do it. The dual openings also limit the possibility of a single opening being blocked and starving the boiler or water heater for air. Don't blame me, I voted for the old war hero and the business expert!!!! endstream endobj 402 0 obj <>stream So the combined input rating is 120 when measured in 1,000 BTU/hr. Depending on the year of construction and the style of the dwelling, there are several ways in which combustion air is provided to the home. %PDF-1.6 % Design, CMS, Hosting & Web Development :: ePublishing. Helping You to Do It Yourself! If the room does not have that much space, you can install a combustion air fan to introduce air to the room. Whether one or multiple, including gas boilers, the same rules apply. To determine if a room is a confined space you add up the gas input ratings of all the gas appliances in the space, measured in BTUs per hour (BTU/hr). 50 cu. There are two basic ways for your furnace to get its combustion air. So a 10 inch by 10 inch opening with a metal grill has a net free area of 75 in2, while a 1010 opening with a wood grill has a net free area of only 25 in2. You can connect the furnace room to the rest of the house with two permanent vent openings. 400 0 obj <>stream i would make the seller definitely fix the problem and put a combustion air vent back in. Wire the fan to operate any time the water heater or boiler is operating. 1FW$3+,X"6*[Jl3?8\pwq15I> According to the Housing Industry Research Center, the definition is as follows: (http://hisearch.org/C.aspx). Photo credit: Ray Wohlfarth, When combustion air openings are blocked, such as this one, boilers and water heaters can be starved of air. For example, lets look again at our situation above where we have a furnace with an input rating of 80,000 BTU/hr and a water heater with 40,000 BTU/hr. I see many boiler rooms with the combustion air opening accidently blocked by either leaves or garbage or purposely blocked by wood or cardboard. ft., or a boiler room roughly 32 ft. by 32 ft. One-inch free area for each 4,000 Btu/hr. Didnt have enough combustion air so I fixed it, the journeyman said. i blxKfhjg,\\,]]=>/` rj@ h\A The journeyman was fired by the boss and I was reprimanded. hj\G_EOpvHHJ E!BBwNSxg7f If the furnace is in a small room, then we need ventilation openings in the walls or door of that room to let in plenty of air to make up for the air that the furnace is using. of free area required. With standard efficiency appliances, flue gases rise up the flue and out of the house because theyre warmer than the surrounding air. The free area of an opening determines how much combustion air can be delivered to the boiler room. We need to get more combustion air from somewhere, and there are plenty of options for doing that. If the door is fully louvered over its entire surface then this will work as long as the combined input rating of the gas appliances is less than 175,000 BTU/hr. So we can put openings in the wall of this room, so long as the openings lead directly into other rooms with a combined volume of 6,000 ft3. If we assume the free area of each metal louver to be 75% of the total size, we would need two grills each sized at 80 sq. 0E2;B Ev! A4B]<>F_NWt2TmX+p fZD3{Krta0!k = - In that case there is no drop in air pressure and you cant get the bottle to collapse. A mere -3/100 in. Many residential boiler installations are relegated into a small closet and expected to work properly. For a better experience, please enable JavaScript in your browser before proceeding. JavaScript is disabled. Figure 2. 240 x 50 (cubic feet per 1,000 Btu/hr.) Normally 2 separate supplies of air are brought in: one high (for ventilation) and one low (for combustion). By visiting this website, certain cookies have already been set, which you may delete and block. input of gas burning appliances in the room. Your appliances that burn natural gas (usually just called gas) are just the same. The Fora platform includes forum software by XenForo, http://www.questargas.com/brochures/59050.pdf, VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. And the drop in pressure is caused by the furnace pulling combustion air out of the room and sending it up the flue. This can be through crawlspace vents for crawlspace appliances, exterior wall vents that allow for air supply through metal ducting for basement and main levels, or simply roof, gable, and soffit vents for attic installations. How do you earn Professional Development Hours each year for your license? And of course if you have any questions feel free to contact Nations Home Inspections. I know they're required to be within 12" of the ceiling and 12" of the floor but nobody ever explained why two are needed instead of one. In this example well say that the furnace has an input rating of 80,000 BTU/hr and the water heater has an input rating of 40,000 BTU/hr. Assuming we have a 12-ft., high ceiling, our boiler room would require an area of 1,000 sq. So of course its important that the flue gases be sent to the outside. = 12,000 cu. input of gas burning appliances in the room. As a service technician, I believe we have a duty to explain to the owner the importance of combustion air. Nations Home Inspections, Inc, (708) 837-6972, fax (708) 445-0725, Steve@NationsHomeInspections.com | Base Content Copyright 2022 Market Hardware, Inc. Additional text content Copyright 2022, Nations Home Inspections, Inc. Websites & SEO for Home Inspectors by Market Hardware. opening is now 75 in. You must have JavaScript enabled to enjoy a limited number of articles over the next 30 days. The building inspector wanted the boiler room to have a fireproof door, sheet rocked and the entire room sealed. So while the furnace is running air is constantly being sucked out of the house and sent up the flue to the outside. So I assume the high/low vents would have supplied additional combustible air to the basement for the water heater. There are some other details that must be satisfied for combustion air. To properly size the combustion air openings, add the input of all fuel burning equipment inside the boiler room. According to the International Fuel Gas Code, Section 304, each boiler room should have two openings, one within a foot of the floor and one within a foot of the ceiling. This is as general of a question as I can ask, what is the purpose of having both high and low combustible air supply vents. I was a young apprentice working with a journeyman technician in a boiler room and he explained how to determine the combustion air required for a boiler room. The most common fossil fuel heating systems we see in Colorado are forced air furnaces fueled by natural gas. Same idea with your furnace. If there are two permanent openings in the appliance space then one must start in the top 12 inches of the space and one must start in the bottom 12 inches of the space. This is basically a big exhaust fan, pulling air out of the house. One of these openings must be located within the top 12 inches of the appliance space, and one opening must be located within the bottom 12 inches of the appliance space. If a gas appliance is in a bedroom closet then the closet door must be solid, self-closing, must be weather stripped to make it air tight, and the gas appliance must get all its combustion air from outside. Usually a metal grill reduces the free area by 25%, and a wood grill reduces the free area by 75%. I offer to remove the blockage and if they refuse, will put something in writing advising them of the danger. Note that this requirement is for the free area of the opening, so if you put some sort of vent cover or grill over the openings you have to take that into account. Warm air rises. These flue gases contain lots of bad things including carbon monoxide, which is deadly. If something happens, you were the last one there. If you are using motorized combustion air dampers, ASME CSD1 code calls for an interlock on the driven damper to not start the boiler until the damper is open. Remember, those flue gases are unsafe and are likely to contain carbon monoxide.
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