Jerry Simon Posted April 29, 2020 Report Share Posted April 29, 2020 The gas-fired furnace and hot water heater are located in a garage closet. Zero air-intake source from the garage. Took me a while to figure out why the furnace's exterior air intake flue pipe had been *tee'd* with an open-end pipe stub. Do you know why? Quote Link to comment Share on other sites More sharing options...
Marc Posted April 30, 2020 Report Share Posted April 30, 2020 (edited) 5 hours ago, Jerry Simon said: The gas-fired furnace and hot water heater are located in a garage closet. Zero air-intake source from the garage. Took me a while to figure out why the furnace's exterior air intake flue pipe had been *tee'd* with an open-end pipe stub. Do you know why? To augment the exterior air intake? Its a garage closet so, what's the harm in taking air from the inside if its unconditioned and available? Edited April 30, 2020 by Marc Quote Link to comment Share on other sites More sharing options...
Les Posted April 30, 2020 Report Share Posted April 30, 2020 I give up. Why? Quote Link to comment Share on other sites More sharing options...
Jerry Simon Posted April 30, 2020 Author Report Share Posted April 30, 2020 (edited) Hey Mark, no, not to augment anything. And, you can't take intake air from the garage with the furnace closet located solely in the garage; if a car is warming up in the garage, automobile-generated CO could be drawn through the ductwork into the living areas Edited April 30, 2020 by Jerry Simon Quote Link to comment Share on other sites More sharing options...
Jerry Simon Posted April 30, 2020 Author Report Share Posted April 30, 2020 1 minute ago, Les said: I give up. Why? For the hot water heater's combustion air supply, you silly. Quote Link to comment Share on other sites More sharing options...
Marc Posted April 30, 2020 Report Share Posted April 30, 2020 54 minutes ago, Jerry Simon said: Hey Mark, no, not to augment anything. And, you can't take intake air from the garage with the furnace closet located solely in the garage; if a car is warming up in the garage, automobile-generated CO could be drawn through the ductwork into the living areas Ok, I misunderstood. I thought you were asking about the combustion air intake for the furnace. 1 Quote Link to comment Share on other sites More sharing options...
Chad Fabry Posted May 1, 2020 Report Share Posted May 1, 2020 11 hours ago, Marc said: Ok, I misunderstood. I thought you were asking about the combustion air intake for the furnace. That is the combustion air... or wait, is that the exhaust that also heats the garage? Quote Link to comment Share on other sites More sharing options...
ejager Posted May 1, 2020 Report Share Posted May 1, 2020 On 4/30/2020 at 6:51 AM, Jerry Simon said: For the hot water heater's combustion air supply, you silly. Smart-ass question: How does the furnace know to only pull the air from outside and not from the closet? More serious question: Is this an AHJ accepted thing in your area? Quote Link to comment Share on other sites More sharing options...
Jerry Simon Posted May 2, 2020 Author Report Share Posted May 2, 2020 9 hours ago, ejager said: Smart-ass question: How does the furnace know to only pull the air from outside and not from the closet? More serious question: Is this an AHJ accepted thing in your area? Not a smart-ass question. The furnace closet doors have an air-tight perimeter weather-stripping/gasket and spring-loaded hinges to prevent CO from the attached garage from getting into the closet. AHJ acceptable? Who the hell knows. The thousands of IL cities/town all march to their own drums. Not to mention the Country of Chicago codes. Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted May 2, 2020 Report Share Posted May 2, 2020 What's the BTU/hr input rating of the furnace? Quote Link to comment Share on other sites More sharing options...
Jerry Simon Posted May 2, 2020 Author Report Share Posted May 2, 2020 5 hours ago, Jim Katen said: What's the BTU/hr input rating of the furnace? The exact rating so the necessary amount of intake air for both the furnace and the hot water heater is supplied by this pipe. 😎 I do get your point; the pipe is likely under-sized. Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted May 3, 2020 Report Share Posted May 3, 2020 If it were a 60,000 btu/hr furnace and a 40,000 btu/hr water heater, that'd be a total of 100,000 btu/hr. The single-opening combustion air method requires an opening with a cross-sectional area of 1 square inch for every 3,000 btu/hr of all the appliances in the space. That would be 33.3 inches. Schedule 40 pvc pipe has an interior diameter of just a shade above 3". So (1.5 x 1.5)x(pi) is about 7". So if you had another 4 of those pipes, it'd be fine. Quote Link to comment Share on other sites More sharing options...
ejager Posted May 4, 2020 Report Share Posted May 4, 2020 Jim, those are some interesting specifications for single pipe. That pipe alone should be easily able to serve the furnace alone, as would another single pipe like that for a direct vent water heater. Do you know what the logic is in making a single source have to be so much larger? Quote Link to comment Share on other sites More sharing options...
Jerry Simon Posted May 4, 2020 Author Report Share Posted May 4, 2020 (edited) 13 hours ago, ejager said: Jim, those are some interesting specifications for single pipe. That pipe alone should be easily able to serve the furnace alone, as would another single pipe like that for a direct vent water heater. Do you know what the logic is in making a single source have to be so much larger? Not disputing your calculations, Jim, but every other furnace I've seen like that (sans water heater issue in my original post) has same size intake-air pipe. They've all been wrong? Edited May 4, 2020 by Jerry Simon Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted May 4, 2020 Report Share Posted May 4, 2020 The single-opening combustion air method does not apply to direct vent appliances. Those have their own dedicated combustion air pipes. The two are not comparable. As soon as you make an second indoor opening in the pipe, as was done in Jerry's original picture, that appliance is no longer set up in a "direct vent" configuration. Now the room needs to have adequate combustion air - generally much more than you'd need if you direct-vented the appliances. Quote Link to comment Share on other sites More sharing options...
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