Thanks for all the great info guys. I'm pretty anal so I think that avoiding creosote and ash build up whether it be in a tee or an elbow won't really be a problem.
However, I have a 30' chimney and the draft is probably going to be pretty strong. I'm thinking about and have been told I should put a key damper inline somewhere. My thinking is that with the 2-4 inches I'll have above the top of the stove, I could put a damper at near the top of the elbow or tee right before it attaches to the liner. This way I can just reach straight back and adjust it if I need to. Does this seem like a logical idea?
BUT I just came across this on woodheat's site:
"A little confusion and bad advice about flue dampers
Hi.
I found woodheat.org to be quite full of information. My first wood stove has been installed, and I'm not sure how to use the flue damper and air inlet supply on the stove. What is the purpose of the damper and how should it be adjusted during various burn times? How does the stove's fresh air supply and the damper work in conjunction? For instance, if one is wide open should the other be, and vice versa?
Look forward to your response,
Rich
Rich,
I don't know what stove this is, but operating instructions are usually provided by manufacturers and those should be your main resource. In fact, we don't recommend the use of flue dampers, unless what you have is a bypass damper that is part of the stove. But I don't have enough information to help you much.
John
Rich replies:
Thanks for the response. The stove is a Waterford Ashling Woodburning stove. It is set up with a rear horizontal flue. Approximately 14" from the flue spigot flange is the damper. The store I purchased the stove from included the damper. I just assumed this was the correct procedure. As a matter of fact there is no mention in the owner's manual about using a flue damper, only the primary air settings. This seems to support the statement -"we don't recommend the use of flue dampers". Why should I not be using the flue damper? A friend has beaten into my head that the flue is critical in controlling the amount of heat the stove puts out. He said if there is no damper or the damper is opened all the way, the heat just goes up the chimney. The Ashling has a 'top air duct assembly' and a 'top plate' with (for lack of proper verbiage) baffles. My interpretation of this design is that these two items are to collect and radiate the heat built up in the firebox. Yes, No? I am very surprised that a wood stove store would promote the use of key dampers.
Rich
Rich,
A flue pipe key damper should only be used when you can't control the rate of combustion from the front end using the stove's combustion air control. Key dampers are associated with various forms of smoke spillage into rooms, the simplest being when someone opens the loading door without first opening the key damper. But key dampers are also implicated in cases in which, as the flue temperature falls towards the end of a burn cycle, draft collapses and the restriction offered by the key damper can produce a condition in which the easiest path for exhaust is out through the combustion air control or any other leak or opening in the appliance. This is not very common but it does happen with cooking ranges or sidedraft wood stoves with rear exit flue collars, for example. The rear exit on your stove makes this a possibility.
Key dampers are only acceptable for non airtight appliances, such as old cast iron "non-airtight" box stoves. Flue pipe key dampers restrict flow even when open, provide a place for creosote to build up and make the flue pipe harder to clean. Your friend has expressed the conventional knowledge related to key dampers; that they prevent heat from being lost up the chimney. But what counts is the rate of flow of gases through the system. The faster the flow, the lower the heat transfer efficiency. If you can slow down the flow to give time for heat transfer, it doesn't matter how you do it. It is incorrect to think that only a damper downstream of the combustion chamber can 'keep the heat in'. By controlling the amount of air allowed into the fire with the air control, you have only one control to manage and you don't suffer any of the downsides to key dampers.
I'm not familiar with the Ashling so I can't comment on the fancy terms used to describe its innards. It could be that the first is just to keep the door glass clear and the second is to improve combustion and heat transfer. Most modern stoves have these components, but some manufacturers like to dress them up with fancy terms.
John
Rich replies:
Thanks for your help. It's interesting how some stores are in business only for the buck. The store I purchased the stove from never asked about the original flue, nor fireplace. They simply stated 'buy this, that and that, and we'll install it'. After a bit of research I opted not to listen to them and had a chimney sweep install a double wall solid pack chimney. It cost more monetarily, but provides greater safety and peace of mind. I appreciate your response to my questions, and will control the burn rate using the stoves intake only and leave the damper wide open.
Thanks, Rich"
That exchange made a lot of sense to me. Are the air controls on a Jotul F3 CB efficient enough to control a strong draft from a tall chimney? If so, then I'll forgo the key damper.