Join Date: Mar 2005 Posts: 78 Received 0 Votes on 0 Posts
How to stop water heater vent backdraft? I’m having a problem with my gas-fired water heater. The vent stack develops a backdraft in the following conditions: very cold outside air temperature, windows and doors all closed, exhaust fan running inside the house (bathroom vent or drier). So when the water heater fires up it vents into the basement until the draft reestablishes. I need to brainstorm the forum because I haven’t come up with any satisfactory solution so far. Let me describe the setup: the vent is three-inch B-vent through the roof. The vertical stack is well toward the edge of the roof, well below the peak. The rain cap is about two and a half feet above the roof. The water heater is offset from the vertical stack about six feet. The horizontal run has an incline of only about 10 degrees. The horizontal run starts about two feet above the vent cap on the heater. So far, I’ve been advised to (1) get a power-vent water heater for over $1200; (2) increase the height of the vent above the roof to above the peak (this would add about six feet…not only looking ridiculous but probably fall over in a high wind.) I also think this isn’t the problem or it would be correlated to wind direction and velocity, and it’s not. (3) install a draft inducer, but I can’t find a source for one that fits the size vent pipe I have. My questions: (1) do you think a draft inducer will solve the problem? And where can I get one? -or- (2) how about if I just increase the incline of the horizontal run? I could lower the height of the vertical portion above the water heater to the first elbow. If I do that, what is the minimum height above the water heater vent cap that the vent pipe needs to be vertical before the first elbow? Any other suggestions for solutions I haven’t heard yet? Thanks for your help.
Join Date: Feb 1998 Location: The Shake and Bake State USA Posts: 10,398 Received 5 Votes on 4 Posts
Hello: skycat First problem is the horizontal pipe. Cannot have any horizontal pipe in any flue pipe that uses natural (upwards) drafting only..... Solution: Raise vent pipe to at least 12 or so inches above roof top. So the cap is in the wind and draft as it is suppose to be and designed to be. The cross winds and velocity create a vacuuming effect that is needed to create yet a more powerful vacuuming effect to aid the natural updraft of hot expanded flue gasses exhausting out of the water heater. Than reinstall vent cap. DO NOT force cap down onto vent pipe all the way. Only enough to secure it with two sheet metal screws. Very common mistake made...forcing vent cap all the way down onto vent pipe. Cannot block the internal vents! Save your $$$$. I highly doubt any force draft vent or power vent will be needed, if all the above conditions are corrected. Be sure the appliance is turned off before attempting any repairs. Always check for gas leaks whenever a repair includes any connection of a gas part, gas line or tubing or gas supply. WATER HEATER HELP LINK:http://forum.doityourself.com/showth...hreadid=159797 CARBON MONOXIDE WEB SITE INFO:http://www.carbon-monoxide-poisoning.com/symptoms.html Web Site Host, Gas Appliances Topic Moderator & Multiple Forums Moderator. Energy Conservation Consultant & Natural Gas Appliance Diagnostics Technician. Personal Reminder: Buckle Up & Drive Safely."The Life You Save, May Be Your Own."
Join Date: Mar 2005 Posts: 78 Received 0 Votes on 0 Posts
Thanks for your reply. I think I'll try increasing the slope of the horizontal pipe first. Is there a minimum vertical length above the water heater that the vent has to be before the first elbow? Thanks.... Can't do anything about the roof vent now...it's too late in the season.
Join Date: Mar 2005 Posts: 78 Received 0 Votes on 0 Posts
Thank you for the link. That had the answer:
Quote:
Originally Posted by hankhill6018 Most area calls for 1/4 inch rise per foot of pipe. However, there must be a 6 inch straight vertical rise coming directly from the draft hood before any elbows.
Join Date: Sep 2001 Location: Kansas City MO Posts: 1,780 Received 0 Votes on 0 Posts
All the answer are fine and dandy under most circumstances but there is still the underlaying problem. A gas appliance starved for air when the house is sealed. You need an outside source of air to the room that the water heater is in. Your heater is currently in a confined space and this what the basis of your problem is. Size wise, you should have a vent not less than 3 inches, but you need 1 square inch for every 1000 btu on the heater. You should have 2 seperate outlets for air, 1 within 12 inches of the ceiling and 1 within 1 foot fo the floor. This will stop any back draft on the heater when other exhaust fansd are ran. Hope this helps...
Join Date: Jun 2002 Location: Northern Minnesota Posts: 1,725 Received 11 Votes on 7 Posts
First off, I'm not a professional, just lots of common sense. Increasing the angle on the horizontal pipe should give you a much better draft. I hate to disagree with a person with almost 8,000 posts but I must. When I installed the furnace in my garage I'm quite sure the top of the vent must be a minimum of 10 feet horizontally from the roof, not above the peak. Unless you have a really flat roof two and a half feet seems a little short to me. With a 4/12 pitch my vent is about 4 feet above the roof. --> You need an outside source of air to the room that the water heater is in. <-- You may have missed this but he said his heater is in the basement. Hope this helps Baldwin
Join Date: Mar 2005 Posts: 78 Received 0 Votes on 0 Posts
I have considered providing additional outside air to the water heater, but obviously being in the climate I'm in, it's not something I want to be always open. It doesn't even have to be a supply to the heater, just something to relieve the partial vaccuum. Perhaps a thermocouple in the burner connected to an electrically-operated valve to open it when the burner ignites? Or a pressure switch that opens it when the pressure drops? I wouldn't have the faintest idea where to purchase such devices. I realize the roof vent isn't up to code, but I'm stuck with it for now. It's not the only thing the building inspector missed in this house.
Join Date: Feb 1998 Location: The Shake and Bake State USA Posts: 10,398 Received 5 Votes on 4 Posts
Hello: Tim The problem is all the above. Must be done to ensure proper air supply for combustion, ventilation and flue exhaust.
Quote: "obviously being in the climate I'm in, it's not something I want to be always open." Not what you want but what is required for any gas appliance.
Quote: "...just something to relieve the partial vaccuum." Primary air supply is the only solution and only safe solution.
Quote: "Perhaps a thermocouple in the burner connected to an electrically-operated valve to open it when the burner ignites?" No T-Couple will function as you stated.
Quote: "...a pressure switch that opens it when the pressure drops?"? None I am aware of are designed for non commerical applications nor any such for the exisiting conditions in a residential home. Nor practical or cost effective. All conditions above must be meet to insure proper operation, efficiency and safety. The choices are always yours and what is in your best interests, however. Existing conditions are not safe.CARBON MONOXIDE WEB SITE INFO: http://www.carbon-monoxide-poisoning.com/symptoms.html Choose wisely. "The Life You Save, May Be Your Own." Good Luck. Web Site Host, Gas Appliances Topic Moderator & Multiple Forums Moderator. Energy Conservation Consultant & Natural Gas Appliance Diagnostics Technician.
Join Date: Mar 2005 Posts: 78 Received 0 Votes on 0 Posts
Quote:
Originally Posted by Sharp Advice All conditions above must be meet to insure proper operation, efficiency and safety. The choices are always yours and what is in your best interests, however. Existing conditions are not safe. I know you mean well and I appreciate your input, so please don't take offence, but recommending solutions which are not possible for me at this time, and then saying that existing conditions aren't safe, hasn't been particularly helpful. I'm looking to improve the current setup as best I can considering what I'm working with. Of course, that isn't the ideal scenario, but then it isn't an ideal world. The current setup was passed by the building inspector during construction and passed by the home inspector during purchase. I'd like to reassure you that I do have a CO detector in my bedroom. Currently it's reading a peak level of 19 ppm. I usually see under 15 ppm after a reset. The manufacturer says it's rated to give an accurate reading over 30 ppm, so levels haven't even reached that threshold. And has never even come close to the alarm trigger of 70 ppm. Not even when I put it in the basement.Again, thanks for your input. All the information learned here is being taken into consideration. Last edited by coaster; 11-28-05 at 07:32 AM.
Join Date: Jul 2005 Location: New York Posts: 723 Received 0 Votes on 0 Posts
Quote:
Originally Posted by skycat I'd like to reassure you that I do have a CO detector in my bedroom. Currently it's reading a peak level of 19 ppm. I usually see under 15 ppm after a reset. The manufacturer says it's rated to give an accurate reading over 30 ppm, so levels haven't even reached that threshold. And has never even come close to the alarm trigger of 70 ppm. Not even when I put it in the basement.
Quote: Our recommendation: safe concentration levels are 0 ( zero), the hazard increases dramatically above 30 PPM. Average occupational exposures above 10PPM (sustained through the work day) are unacceptable if your goal is normal function and good health long term. Out of curiosity, did the home inspector and building inspector test the draft? Or did they just look at the setup? Please don't take offense to this but I believe the convenience of your current situation clearly over rides the health issues involved.As a gas technician for 15 years, firefighter for 19 and emergency medical technician for 12, I've seen a lot from the before and after effects. If I had to service your water heater, you wouldn't have hot water until the corrections are made.
Join Date: Mar 2005 Posts: 78 Received 0 Votes on 0 Posts
Naw -- the only thing I've ever seen the display read in real time is zero. The peak must be happening for a very short transient sometime when I'm not looking at it. There's no way I'm getting 19 ppm over ANY sustained time period. I increased the angle of the horizontal run on the vent pipe in the basement to about 30 degrees. That's all I'm going to get and still have six inches above the heater before the first elbow. Can't do anything outside any more this season. The roof is covered with snow. The home inspector just looked at the setup. I don't know about the building inspector...I'm the third owner. |
How to fix backdrafting water heater
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