I have just installed an older Daka stove in my basement. I have the stove exhaust pipe running up my masonry chimney. And the hot air connected to my natural gas furnace plenum off the main trunk line with (2) 6" duct lines I also have a furnace blower attached to the stove to move heat around my house. However I have realized that, even with the bigger furnace blower I'm not getting very much air flow to the main floor of the house. Could it be because I do not have the blower attached to the cold air return on my existing natural gas furnace? Or maybe because the (2) 6" duct lines are to small? Almost as if I am trying to pump hot air into rooms that I'm not taking air away from. I don't know if that makes any sense to you guys or not. Any suggestions or advice is greatly appreciated! Thank you. Sent from my SM-N981U using Tapatalk
Welcome to FHC AK! I see a couple things right off the bat...first thing is that its a DAKA wood furnace, not stove. Second is the (2) 6" lines are too small, especially going that far, and using that flex pipe...that stuff has terrible flow characteristics. Many/most wood furnaces that are considered "add-on" like that use at least (2) 8" pipes...and 8" pipes will flow almost double what 6" will. Do you have a backflow damper in the gas furnace plenum? If not then the air can take the path of least resistance...which might be the return air ducts, or supply, or both (is that a downflow gas furnace? If not, then it looks like you are connected to the return air drop?) And as far as the return air, try opening the door to the basement...if that helps then you answered your own question.
Thank you for getting back with me. You are right it is an add on wood furnace. All I had before was a small wood stove haha. As per my hook up the flex duct is only covering the last 4' I needed to get to my main plenum. I am not hooked up to my cold air return. The (2) 6" lines go behind and around my cold air return for the gas furnace. And are connected to the supply trunk? I cycle my natural gas furnace blower for 15min every hour just to get a little boost in air flow. I do not know if there is a back flow prevention in the main trunk. I was thinking of getting rid of the 6" ducting and replacing it with 8" x 14" square duct But also making a box around my blower and connecting that to the cold air return from my natural gas furnace. In my mind that would give me much better air flow.. Like my natural gas furnace blower does. This is my first ever wood furnace so I don't know much about the ducting and air flow. As I am on my 3rd blower trying to get better flow. The door to my basement is a Dutch door ( half door ) And above the wood furnace is an old laundry shoot that is still wide open. Sent from my SM-N981U using Tapatalk
If you didn't add a backdraft damper, there isn't one...and you need one. Upsizing the duct is a good idea, (56 sq in now, vs 112) but, you need to watch that you don't get too much flow...otherwise the blower will cycle on/off all the time (old school wood furnaces tended to do that some anyways) especially if you have upsized the blower already (explains why the blower looks way too big for (2) 6" supply duct pipes) If you have a dutch door then there is no issue getting return air...but, pulling cold air off the basement floor will lower the temp of the warm supply air coming out the top side...10* less is pretty common. And just so you know what to expect...a wood furnace will never provide the airflow that a fossil fuel furnace will...the fossil fuel furnace is running at full BTU for a bit, and then shuts off for a while...a wood furnace runs at full BTU only for a bit (normally) then "idles" most of the time, (6-8-10 hour straight burning) so the fire can't be too big, or it would be 100* in the house...that means the duct airflow needs to kinda "match" the heat output...otherwise you get that blower cycling I mentioned (drives me nuts)...and when the blower is not running, the heat is all going up the chimney, none (very little) to the house. Its like the tortoise and the hare...gas is the hare, wood the tortoise...gas goes like heck and shuts off (naps) the tortoise just keep plugging away, and wins. Gas = higher duct temps/higher air flow Wood = lower duct temps/lower air flow
Do not hook up ductwork from your wood furnace to the return air of the gas furnace. Rather, build that box (return air plenum for wood furnace) out of sheet metal and connect to the return air drop from the gas furnace. Be sure that you allow the air to be filtered before it reaches the wood furnace blower; you will have to incorporate this also into that box. Build a plenum out of sheet metal to be connected to the discharge side of the wood furnace which covers both of your 6" holes. This can be a simple square box. Connect that wood furnace plenum into the gas furnace plenum with round pipe.....absolutely no smaller than 8"! Somewhere in this round pipe connection, preferable as close to the gas furnace as you can, install a manual damper which can serve as a backdraft damper. It is the same as a key damper in a flue pipe. If you run the wood furnace, place in open position. If only the gas furnace is used, close this "backdraft" damper. If you don't, the sir will find the easiest path once the gas furnace blower turns on and the heated air from your gas furnace will probably end up blowing towards your wood furnace. When you hook up the round pipe from the wood furnace to the gas furnace at the plenum of the gas furnace (whew) place a 90 elbow on the inside of the gas furnace plenum facing upwards......such as diagram shows. This will aid in air distribution from wood furnace to existing ductwork. You want to avoid the chance of any wood furnace air being run across the gas furnace. This is why you don't want to hook up the supply of the wood to the return air of the gas. (I don't think thats what you had in mind, but it is too important not to mention) All of this ductwork and pipe used should be of metal. Ideally, the wood furnace should have been placed as close as possible to the gas furnace to tie in with the ductwork. Its not too late for that, either. Looks like it could be repositioned 90 degrees so that the wood blower is facing towards the gas return air. Hard to consider everything judging from only one pic though. I'm wondering if you get dust (ash) in the house from the hook up the way it is? (Used to be there decades ago!) This next image shows duct work and tie in of wood to gas but also shows "automatic" backdraft dampers installed. This last image shows the return air plenum for the wood furnace where you would install air filtering capabilities. Keep us posted on your project, please.
Wow. Thank you both brenndatomu & yooperdave for all that awesome info! The walls of this wood furnace get pretty hot and it throws off alot of heat. If I were to move the wood stove 90° closer to the gas furnace it would be too close and could potentially cause damage to the gas furnace. I know that the picture does not do any justice in seeing where everything is. yooperdave, Those pictures you had posted is exactly what I was thinking of doing. Built all out of sheet metal I was thinking of building a plenum on top of the wood furnace. Now for connecting the wood furnace plenum to the gas furnace plenum, could I use square or rectangle duct? I don't have to, but it would make it look a lot cleaner if I can get away from the 8" round duct. Sent from my SM-N981U using Tapatalk
Okay guys, So I was doing some research on ductwork on what would be my best option to go with (Funds are running low due to pandemic) This is what I could come up with for my budget And I wanted to run this by you guys and get your thoughts before I went and did anything. Building a plenum on top of wood stove and running (1) 12" duct to distribution trunk it would look somthing what I have in picture. Do you think that would be sufficient enough? Sent from my SM-N981U using Tapatalk
We used to rate/allow 6oo/650 cfm for 12" round pipe. Should be fine. I have seen homes heated with 10" that worked also. The 8 X 14 square duct would carry the same in case that route saves you $$. The more 90's you put in the ductwork, the more resistance you end up with. If you can, go with the round pipe. Sometimes, if you know anyone in the HVAC business, you can pick up some odds and ends of duct work that is just thrown out anyway. Might pay to ask?
Okay then round pipe is the way to go. That will fit my budget. Sadly I don't know anyone in the HVAC trade. I'll keep you all updated with this project as I progress through it Thank you all again. Sent from my SM-N981U using Tapatalk
Where are you located akeller ? Menards around? They sell plenum kits pretty cheap...really, all their premade ductwork is pretty reasonable IMO...especially if it allows you to DIY, instead of calling in HVAC to do it ($$) Just don't use flex duct...it flows poorly, and the "plastic" stuff is not rated high enough for wood furnace duty.
I'm located in Michigan. And yes there is a menards about 30min away from where I live. Earlier when I said I was doing "research" lol I was actually on the menards website looking up prices of all the ductwork pieces I would need to complete this project. Menards is like my second home. I'm there all the time. Alot of projects over the last few months And to complete this project it would cost roughly $170. For all the parts i would need to complete. (1) Plenum kit 20"x20" x36" - $58.30 (3) 12" elbows -$38.16 (1) 12"x60" -$25.44 (3) 12"x24" -$$48.30 = $170.20 Sent from my SM-N981U using Tapatalk
I seen their ad this morning (well, didn't actually get it to open...need to try that again now) and it said this is the last 11% sale of the year...
akeller you can save a little more $$ by buying 6" by 60" round pipe instead of 12" round pipe. For instance, if you need 60" of 12" pipe, buy 2 lengths of 6" by 60" pipe and snap them together so the puipe will be 60" long but have two seams instead of one. The price of 6" by 60" 30 ga pipe is about $8 before 11% rebate. Sounds a lot better than that over $25 you quoted..... Surprisingly, 26 ga isn't too bad either....less than 28 ga!
you know that is actually a good idea. I never thought of that. Is a really good way to save some cash forsure. I'll have to look into that. It might be even cheaper to do it that way for the smaller pieces as well You don't think the heat from the wood furnace would be too much for a pipe with 2 seems? Sent from my SM-N981U using Tapatalk
Try the 28 ga if you're concerned about the heat. I know there were some guys that hooked up a temporary furnace (non-high efficiency; so it had hotter exhaust) with 6" exhaust but 30 ga thickness. This furnace ran that way for a few months during construction phase. Well, take back what I said about 26 ga being less than 28 ga pipe. I can't find it again! Dang this computer....
I guess I can't be to worried about the heat. I mean I have been running this wood furnace all week long. Sent from my SM-N981U using Tapatalk
