Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Snowdooer, Nov 25, 2008.
I know how you feel I've got 2600 sq ft they don't tell you this stuff in the brochure
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When you installed the 16 x 8 duct, did you cut it right into the top of the furnace or put the 2 8's into it? The guy who helped me with my furnace install also said never to use 90s and that each 90 takes away 2 inches of interior capacity of your 8 inch pipe, so having the 2 90's was really restricting your airflow. The original blowers that come with that furnace don't do well with any resistance. 175 seems like a high set point to me.
I did use the 8" round directly out of the furnace and transitioned into the 16x8. I've attached an updated picture of my installation that shows the 16x8 duct installed.
Last night I played with an "auxilary blower" from an old oil furnace to increase flow. Funny thing is, as I raised the speed on that blower my plenum temps came up, but I still didn't get any heat in to the house. Very strange.
I tried the suggestion of running the propane furnace's blower in conjunction with the wood furnace. That didn't work. All I got was a bunch of cold air into most of the house and warm air in the runs closest to the wood furnace. The blower on the propane furnace is too strong and restricts the flow of the wood furnace blowers.
I also made up some turning vanes and placed them in the last 16x8 elbow before entering the main trunk line. That didn't help either.
A co-worker of mine gave me a couple in-line duct booster fans to try. They are basically 2 4" fans mounted side by side on a 4x10 plate that screws to the bottom of the trunk line. They have a 400 cfm rating. I'll give them a shot tonight and see what happens.
put 2 90 up and into the main trunk line. this will get the flow down the main line. i did this with my englander and i heated the wholw house 2000 sq ft 2 story in new hampshire, on the side of a mtn. facing north. good luck.
I'm not exactly getting what you said. I'm still on coffee #1, can you explain further.
What 90 deg elbows? The 8" round" Get rid of them?
I think the only problem you are having is airflow and those little blowers on the back. I would bring that square duct all the way over the wood furnace and then cut out the top of the wood furnace and make a plenum that goes up to the square ducting. I can't see the back of your wood furnace, but will that big blower mount to the back? If not, I would put it on the side of the wood furnace, you could even turn your stove sideways so you could hook to the return easier. I would change your setpoints to something like 140-90 so it runs more often and circulates more air. I have a thread on here about my stove which shows the plenum I cut into my furnace and you can also see where I had the big blower into the side before I changed it to what I have now. The big blower helped, but I still needed more airflow, so I changed it again.
I was thinking of adapting the big blower to my furnace, but I was afarid of putting too much air flow past the heat sink and losing temperature. The manufacturer also warned me of this too. The blower will fit, but I have to cut out the back of the stove, so it's a modification that is hard to reverse. Same with the top. Once I cut out the top it would be hard to go back.
My gut tells me I should do it, but my wallet keeps stopping me.....
I think you would be fine with that mod. iam pushing 2500 cfm still very warm at the at each out let
Check out my 1557 build thread on here. I have a 100K btu propane furnace blower blowing right through mine. I cut a 13x30 hole in the side and another hole in the top and with a decent fire, my blower runs near constant with a 110-90 thermodisc. Also, you are going to be heating your return air, so you would only need a 30 degree or so temperature rise out of your furnace. Your furnace was made with a blower made for I believe 1100 cfms, but with any resistance at all, you aren't pushing anywhere close to that. The bigger blower would have enough force to get the air flowing. You could use a dimmer switch/rheostat to control your fan speeds for more options. Is that a multi speed fan? You could wire a hi/low switch if so.
Yes, the blowers are rated at 1100 cfm. I can tell by sticking my hand in the main trunk that I'm losing some of the flow. Those blowers only have a 1/25 hp motor and can't handle much back pressure. The other furnace fan I have is a multi-speed fan. That's a good idea putting a hi/low switch on it.
Maybe I'll start by cutting the return side and getting more flow through the furnace on that end. It's a pretty quick mod and won't take that much sheet metal. The top of the plenum is a much larger job. If I still don't get the flow I'll go that route.
I took a look at your build. Very nice. I wish my two furnaces were close enough to do that, but I'm stuck in that regard. Looks like I found something to keep me occupied this long Thanksgiving weekend!
When you remove the small blowers, take a look inside. If I remember right, I didn't put the big blower in the back because there's actually an inner metal wall you have to cut through, but only the one on the sides. When you look inside, I think you'll see what I'm talking about. Keep us updated with some reading over the long weekend. Happy Turkey day.
I'll take a look, but the last time I had a blower off a vacuumed out the plenum and don't remember the inner wall being there.
BTW, is there a reason why you didn't try and just buy a bigger motor for the stock fans? I had someone suggest to me that I should just replace the 1/25 hp (1550 rpm) motors with something like a 1/10 hp (3600 rpm) motor and get higher flow that way.
I'm getting kind of sick of the $$$ of this R&D;project myself and I'm leaning towards following your lead, but though I would ask.
your duct work in place just modding the blower and your going to love the system just try and work with what you have.(2000-2300 cfms and your there)
the air flow needs to go down the main trunk.if you just have the pipe stuck in the trunk at a 90 you are just spalshing the air in there not in any direction.a 90 set into the main trunk will direct the flow where it needs to go.
Thats a good place to start but those 2 550cfms blowers will still be way under powered
I'll do some more playing tonight and Friday and keep you guys posted as to what I find. Thanks again for all your suggestions and information.
please do and take pic's
I did look around for blowers that would fit in the stock holes. Like you said, all you'll find is 1/10 HP and I wanted 1/3 or 1/4 HP to get the air moving. I'd rather go too large and use low speed if I had to than buy another problem. Plus, the big blower was only around $80 shipped. Looking forward to seeing the pics also...after 3 years of trial and error with mine, I'm out of mods that I can do to it, so all I can do is read about other people's trials. You'll see a huge difference once you get the blower in.
matts right easier to throttle down than have no peddle left!!
I'll chime in here. Just because you are moving more air around the jacket, does not mean the air will cool the firebox, or the heat at the registers. I was one of the few a couple years ago that was fed up with the old install. I can push around 130 degree air from all of our registers in our home, running at a firebox temp of 400-450. If you get a bigger blower, you need to just cut the back, or side out to accompany the blower. Also you should have a honewell limit/control, and not a snapdisc. This allows you to set your temps so the blower runs for a while with heat. With that setup and runs, you need more than 2 8" ducts. Also I would setup a damper above the main furnaces plenum, that way you shut that off to allow for pressure in the system with a bigger blower. Its frustrating having to spend the $$$$$ especially in this economy, but it will pay off if done correctly. I ducted mine in series, that wont work for you, but you can get alot better heat from a few modifications.
A damper plate in the main trunk line to prevent heating your idle furnace is probably the cheapest route to take and will help even with the bigger blower. I did it with the US Stove Hotblast and bigger Englander I had and forced the air throughout the trunk line. Pretty simple to make too! 1'8" steel rod for the axle(I used copper coated acetylene weld rod). Flat sheet metal (flat duct work is good enough) at 1/8-1/4" narrower than the trunk width and about 1-2" taller than the trunk height. Center and attach the axle to the center of the damper plate width-wise[(flat sheet metal) I used one simple cabinet hinge that I took apart] . Drill 1/8" holes centered and aligned in the trunk line for the axle to fit through. 5-8" fully threaded screw or rod to attach weight to (for counter balance) (at head end which is furthest away from damper plate) and spring (to keep weight in place, use lock nut on one side of damper plate and regular nut with washers to hold counter balance screw to damper plate) about 1/3 down. Put enough weight out to the end of the screw to allow the plate to "gravity" swing shut (block air from wood furnace to gas furnace) but also blow open by the gas furnace blower. I used a long rivet (just before center from the top about an inch in from the farthest reach of the plate as it swings) in the trunk cabinet line to prevent the damper plate from swinging past center and locking the plate closed to the regular furnace. Pin or clamp (slight groove in axle with hair pin cotters and small washers for axle movement) the axle and damper plate so it don't shift from side to side but still move up and down for it's cycle.
Just a project if you choose. I used this set up for about 17 years. Oiled the hinges every couple of years and cleaned the cabinet (once) where the damper plate goes (as close to your gas furnace as you can get). No real problems...Stay warm
OK boys....I am sitting here in my 75 deg living room typing this post. First off; thanks to all of you that helped me out with advice. I've been beating my head against the wall for weeks trying to get this furnace to heat my house. Now after following your advice I just need to learn how to control the burn and keep my house under 80F!
I spent yesterday making the mods to my furnace. I ended up cutting a larger hole in the back of my furnace and installing a single blower with a much larger capacity. I also modified the return air duct to accept the larger blower. I was going to open up the top of the furnace (and I still might), but by just adding the larger blower my house is plenty warm.
The reason I might still open up the top is that I am noticing hot spots on the furnace skin surrounding the air box. Oddly enough the hottest spot seems to be around the limit control. I figure by opening up the top it might change the air flow around the firebox enough to get better mixing.
Here are some pics of my modifications:
I read a couple other posts that talk about removing the rear forced draft plug for use as secondary combustion air. I'm going to experiment with this (once I can get it removed) to see if I can get a cleaner burn. I have a wood stove in my living room (quadra fire) that has secondary combustion air tubes across the top. I'm wondering if anyone has made this mod using the forced draft plug as a source of air? I don't think it would be too hard to fabricate.
Someone from arboristsite.com did it with black pipe. Said it makes a difference. Just removing that plug will give close to the same effect. I would for sure open that top up. You will get alot better flow through the furnace. Looks good, and glad you have found what you were looking for. Forgot to add, I would turn down your on to 140. That way you don't have to have a roaring fire to kick in the stove. When it starts to burn the coals down you will get more heat from the unit. I am at 140 on and 85 off. It works the best for me.
Very neat looking install, looks like you are good at fabricating ductwork. Just keep playing with the dampers until you get it comfortable in the house. I tried taking that back plug out and it just lets in a lot more air which doesn't work well for me with regulating the temperature in my house, but it may work for you. Can you dump some of the heat into the basement? I had to move my limit switch to the right side because just like yours, that left corner was hotter than the rest of the furnace. Just drill another hole and fill the old one.
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