Not knowing how or what stack to use with your waste oil furnace can cause problems and may even be dangerous. Not using the proper fireguards and understanding clearances can literally burn down your shop. In addition to safety hazards, improper stack can cause damage to your furnace and destroy critical components in your burner. If your stack is not correct it can lead to back draft which may lead to costly repairs that would not be covered under a factory warranty. The reason back draft or down draft is not covered by warranty is because it is typically caused by 3 things including improper stack. The other 2 things would be an exhaust fan without proper make up air or a clogged heat exchanger or chimney / stack. The only time it might be covered under warranty is if you have a hole in your heat exchanger during the warranty period. But we can do a whole other article on back draft, so we'll save that for another time. For this article we're going to focus on stack / chimney. Your manual that you received with your furnace should have information on stack requirements. So we're just going to hit the highlights.
*All waste oil furnaces must be installed according to the NFPA 211,3.3.39 and NFPA 31 6.5.16-18 codes which can be found at https://www.nfpa.org/
Many people try to use "whatever" they have available to avoid the expense of buying the proper stack. Over the course of the years I know I have seen and heard of some interesting configurations to say the least. Maybe you have a culvert pipe that you aren't doing anything with so you decide to hook it to your building and run some pipe from your furnace into this thing and let it exhaust however it will. However, the couple of times I have heard of someone doing just that, it costed upwards of $1,000 in repairs. Another bad idea, either because class A pipe is so expensive or you just don't know you're supposed to use class A stovepipe / chimney stack so you do your entire stack with single wall galvanized or black pipe. This is also a very bad idea for the same reason as the last. When the gases that are trying to escape out your chimney hit that cold single wall pipe, they can slow way down and even go backwards. Those mistakes are a couple of doozies. However, one of the most common dilemmas is "I want to use an existing hole in the roof but it doesn't quite line up with my furnace". So in order to get your pipe to that hole you're putting extra elbows or a long horizontal run with no slant. An example of another mistake, in recent days we have come across 2 stack installations that go through the wall with single wall pipe and up the outside of the wall with Class A. So they did go to the expense of buying class A pipe but they don't quite go far enough. Granted, you may have a block wall. So you aren't worried about catching it on fire. But the draft is still an issue. So if you are thinking about stuffing a piece of single wall through your wall and into your insulated pipe, please don't. I guarantee you wouldn't be the first person to make these mistakes and unfortunately, you wouldn't be the last either. But if you read this article, you'll be that much closer to getting it right. In some situations where you absolutely can't do the proper stack, adding a draft inducer may help. Using a draft inducer to cheat is not to "code". And another consideration is, if you force the draft inducer to do the work, you better make sure it doesn't fail. Obviously if the draft inducer quits working, you're back to the $1000+ in repairs scenario. While I personally would exhaust every avenue before going the route of cheating with a draft inducer, it may be a solution in certain extreme circumstances. So I would advice, do this at your own risk.
Now that we've covered some of the "dont's" and pitfalls, lets look at some of the elements that make a good stack install:
- Use class A insulated stack through any building penetration and for any exterior stack
- Keep horizontal runs short and slope any horizontal section at least 1/4" per foot
- Have properly sized stack (don't go into a stack pipe that's too small)
- Have a minimum of 10 foot of vertical chimney to ensure proper draft over fire -.02" w.c.
- Keep your stack simple - don't have multiple turns that may reduce natural draft. Rule of thumb is to use no more than 1 - 90 degree elbow. Any additional elbows should be max 45 degree turns.
- Install a Class A non-restrictive chimney cap such as our spark arrestor cap by MetalFab
- Make sure your stack is the proper height in relation to the peak of your roof (see diagram)
- Maintain the proper space from any attic insulation or other combustible materials (An insulation shield may be needed particularly with blown in insulation)
- Use the proper supports
- Secure the outside pieces of stack together with stainless steel screws (MetalFab is interlocking but wind over time can work a piece loose)
- Follow manufacturer and N.F.P.A guidlines (trust the experts)
Hopefully now that you've read this article, you're well on your way to understanding how to design a stack installation that will work for you. And you can avoid some of those really costly mistakes. If you have any questions please give Eco Logical Solutions a call (765)449-0113. The stack diagram was provided by Clean Energy Heating Systems of Honeybrook, PA