Positive to negative draft conversion

[Duetech]

I have an EKO40 that I want to convert to negative draft. I will leave the current blower, but switched off, in place as a back up system but I want to put a blower with a long shaft at the base of my clean-out that extends the shaft with a fan blade up past the flue opening of the boiler so it will pull the exhaust from the boiler. OR get another blower similar to the one on the boiler and just run a pipe up through the bottom of the clean out past the flue opening and induce a draft via a high speed venturi type nozzle concept. Do you think the venturi nozzle will have enough displacement to generate the draft I need? Any constructive ideas out there? Thanks for your input in advance....Cave2k

 

[steam man]

I think it would take some experimenting to get this conversion right. Any draft inducer takes a beating from the temperature from the combustion process. I have thought about the "eductor" type setup you mentioned. They can move a lot of air but also take a lot of power therefore not real efficient. I would think that the draft inducers also need more HP to do the same job but that's just an educated guess. If your thinking about the smoke problem during loading there are draft inducers (Terjrlund?) that you may be able to use during loading. I would be interested to know if anybody has used one.

Mike

 

[WoodNotOil]

I have wondered about doing something like this to my Tarm Solo Plus. It seems to me that getting a suction fan that is meant for a Solo Innova and making up your own way of mounting it on the exhaust stack might work. On my older Solo the fan is on the top near the front and that would have to become the primary air control. It would be interesting to experiment with, but there are a lot of variables that make these designs work. Few of us have the engineering skills to fully understand it all, but there is always trial and error. Just make sure you can always put it back the original way.

 

[Fred61]

I think it would take some experimenting to get this conversion right. Any draft inducer takes a beating from the temperature from the combustion process. I have thought about the "eductor" type setup you mentioned. They can move a lot of air but also take a lot of power therefore not real efficient. I would think that the draft inducers also need more HP to do the same job but that's just an educated guess. If your thinking about the smoke problem during loading there are draft inducers (Terjrlund?) that you may be able to use during loading. I would be interested to know if anybody has used one.

Mike

I'm using the Terjrlund. Works good for me for loading and starting a fire.
https://www.hearth.com/econtent/index.php/forums/viewthread/37304/P15/#399100

I ran the wood Gun for ten years and although I had tons of trouble with door gasket leaks, refractory deterioration and premature failure of the boiler vessel, I never had trouble with the fan. The fan was about a foot in diameter which was basically a large motor mounted in a plate with, a bearing that was bolted up to an opening in the rear of the boiler in the so called swirl chamber. It had a steel or cast plate (I can't recall) with impellers welded on the flat surface similar to an automobile water pump. This thing moved alot of air and was not adjustable. The fresh air damper was motorized and the air was directed at the base of the fire. The bearing must have been sealed well and must have stayed fairly cool since I never had a problem with it. I would be concerned about placing a squirrel cage blower in the heat stream because it's pretty whimpy compared to the one in the wood gun. It is also affected by any build-up of deposits on the impeller.

 

[steam man]

I like the concept of a draft inducer. I didn't say in the above post but I have a draft inducer or "Power Vent" on my oil boiler. Although it does eliminate the chimney they are not fool proof. It has a draft proofing switch and a blocked flue burner cutout. It may be for an oil boiler but the motor/bearings have failed (at the worst time). The motor/blower is a little pricey. It requires some regular minimal maintenance-oiling bearings, cleaning the impeller (for balance issues) and it is a squirrel cage type blower. They may not be for everyone. The wood gun's impeller sounds more like my small 3.5 hp lawn vacuum with an electric motor-hey....did I just give someone an idea for a "suction" fan?

Mike

 

[fabguy01]

I have an EKO40 that I want to convert to negative draft. I will leave the current blower, but switched off, in place as a back up system but I want to put a blower with a long shaft at the base of my clean-out that extends the shaft with a fan blade up past the flue opening of the boiler so it will pull the exhaust from the boiler. OR get another blower similar to the one on the boiler and just run a pipe up through the bottom of the clean out past the flue opening and induce a draft via a high speed venturi type nozzle concept. Do you think the venturi nozzle will have enough displacement to generate the draft I need? Any constructive ideas out there? Thanks for your input in advance....Cave2k

I tried that this winter on my OWB my exhaust comes out the back then 90s up. all I did was hole saw a 2" hole in the bottom of the horizontal 8" pipe in line with the center of the vertical 8" pipe and ran a piece of 2" tube up through the center of the vertical pipe creating a nozzel. I just used a graingr 500cfm blower. I like this idea because it keeps all flue gasses and heat away from and out of the blower. It seemed to work OK but the cfm's and the distance from the end of the nozzel and end of the flue create alot of variables. So i think it can be done but it takes alot of R+D.

 

[Duetech]

steam man,
The eductor I am assuming is something like the venturi nozzle principle? The blower on my EKO40 is quite powerful for a small blower and would work in a venturi set up I think as I currently have it's output severely reduced. Sometimes with the blower off and pressure from the hot coals I can get a short term soft gasification and I don't think it would take much to induce gasification enough to heat at least in the shoulder season. There are more powerful low power consumption motors out there so I think that angle is at least worth a shot. The concept I have for a fan blade to induce induction is based on a long shaft that takes the bearings out of the heat path and totally out of the chimney structure. The motor would be mounted on the clean-out cap which is in the bottom of the "T" that connects to my boiler flue. Incorporating the newer EKO controller for variable motor speed would seem a logical inclusion for greater design flexibility and keeping the EKO "peak" temp blower speed reduction principle in tact. The longer shaft seems it would be more sensitive to vibration caused by ash build up and that may mean frequent cleanings.

As far as the tjernlund draft inducer I had (much different than Fred61's) a model on my wood furnace that worked fairly well but I would not think it capable of producing the draft output of the current blower on my boiler as the rpm is low even at the highest setting. As well I have triple wall chimney on my boiler and the Tjernlund is designed for single wall.

The Innova (woodnotoil) blower looks to be insulated from the main heat source of the flue while in gasification mode, especially since gasification exhaust temps would be lower than high volume natural draft temps and from what I can tell from the pic's the blade design is similar to the tjernlund blower so it must by spinning quite fast to work the boiler.

Thanks all for your input. I will see what I can come up with and if I can get a reasonable success story I will post it.

 

[taxidermist]

I have an EKO40 that I want to convert to negative draft. I will leave the current blower, but switched off, in place as a back up system but I want to put a blower with a long shaft at the base of my clean-out that extends the shaft with a fan blade up past the flue opening of the boiler so it will pull the exhaust from the boiler. OR get another blower similar to the one on the boiler and just run a pipe up through the bottom of the clean out past the flue opening and induce a draft via a high speed venturi type nozzle concept. Do you think the venturi nozzle will have enough displacement to generate the draft I need? Any constructive ideas out there? Thanks for your input in advance....Cave2k

Check out the back of a biomass 60 it has a built in draft inducer on the back that runs with the primary fan on the front.

 

[steam man]

steam man,
The eductor I am assuming is something like the venturi nozzle principle? The blower on my EKO40 is quite powerful for a small blower and would work in a venturi set up I think as I currently have it's output severely reduced. Sometimes with the blower off and pressure from the hot coals I can get a short term soft gasification and I don't think it would take much to induce gasification enough to heat at least in the shoulder season. There are more powerful low power consumption motors out there so I think that angle is at least worth a shot. The concept I have for a fan blade to induce induction is based on a long shaft that takes the bearings out of the heat path and totally out of the chimney structure. The motor would be mounted on the clean-out cap which is in the bottom of the "T" that connects to my boiler flue. Incorporating the newer EKO controller for variable motor speed would seem a logical inclusion for greater design flexibility and keeping the EKO "peak" temp blower speed reduction principle in tact. The longer shaft seems it would be more sensitive to vibration caused by ash build up and that may mean frequent cleanings.

As far as the tjernlund draft inducer I had (much different than Fred61's) a model on my wood furnace that worked fairly well but I would not think it capable of producing the draft output of the current blower on my boiler as the rpm is low even at the highest setting. As well I have triple wall chimney on my boiler and the Tjernlund is designed for single wall.

The Innova (woodnotoil) blower looks to be insulated from the main heat source of the flue while in gasification mode, especially since gasification exhaust temps would be lower than high volume natural draft temps and from what I can tell from the pic's the blade design is similar to the tjernlund blower so it must by spinning quite fast to work the boiler.

Thanks all for your input. I will see what I can come up with and if I can get a reasonable success story I will post it.

Take a look at this site. http://www.nciweb.net/eductor_gas.htm. I've used eductors before but never for gases. But then again I have used them for pulling a vaccum in pipes to help a centrifugal pump get suction. They will pull like crazy. The problem with fan design/selection is getting the right cfm at the right pressure. The idea of a long shafted fan may lead to some balance problems. You may want to try using an impeller inside the stack with the shaft extending out each side supported by bearings. If you could get an inducer that is already used on a gassifier you'd be in the ball park. I'd still like to try that lawn vacuum fan. LOL. I may be retiring that thing from service so I may try it as an induced fan on my planned system.

Mike

 

[WoodNotOil]

I have an EKO40 that I want to convert to negative draft. I will leave the current blower, but switched off, in place as a back up system but I want to put a blower with a long shaft at the base of my clean-out that extends the shaft with a fan blade up past the flue opening of the boiler so it will pull the exhaust from the boiler. OR get another blower similar to the one on the boiler and just run a pipe up through the bottom of the clean out past the flue opening and induce a draft via a high speed venturi type nozzle concept. Do you think the venturi nozzle will have enough displacement to generate the draft I need? Any constructive ideas out there? Thanks for your input in advance....Cave2k

Check out the back of a biomass 60 it has a built in draft inducer on the back that runs with the primary fan on the front.

What are the specific advantages of running both the inducer and a positive draft fan? I assume you could have the inducer run on loading and eliminate any smoke problems. Is the rk2001 controller that the Eko and Biomass use setup to run both fans? Does it allow the inducer to be on but not the primary? That is an interesting way to do it and would be a much easier tweak for people with positive draft gasifiers.

 

[taxidermist]

I have an EKO40 that I want to convert to negative draft. I will leave the current blower, but switched off, in place as a back up system but I want to put a blower with a long shaft at the base of my clean-out that extends the shaft with a fan blade up past the flue opening of the boiler so it will pull the exhaust from the boiler. OR get another blower similar to the one on the boiler and just run a pipe up through the bottom of the clean out past the flue opening and induce a draft via a high speed venturi type nozzle concept. Do you think the venturi nozzle will have enough displacement to generate the draft I need? Any constructive ideas out there? Thanks for your input in advance....Cave2k

Check out the back of a biomass 60 it has a built in draft inducer on the back that runs with the primary fan on the front.

What are the specific advantages of running both the inducer and a positive draft fan? I assume you could have the inducer run on loading and eliminate any smoke problems. Is the rk2001 controller that the Eko and Biomass use setup to run both fans? Does it allow the inducer to be on but not the primary? That is an interesting way to do it and would be a much easier tweak for people with positive draft gasifiers.

Yes it is run by the rk2001 controller. It has a door switch on it that when you open the door to load you leave the primary fan on and the door switch cuts the power for the primary fan and leaves the inducer fan on to pull the smoke. I just seen one for the first time last weekend. I was helping sunshinetreefrog with his. I would have bought this unit if I knew more about it at the time I bought my eko.

 

[taxidermist]

Page 9 shows how it is wired


http://www.newhorizoncorp.com/PDF/BioMax07NA.pdf

 

[WoodNotOil]

Are there any other benefits to negative draft other than smokeless loading? If so, does the biomax approach of positive draft with draft inducer accomplish the same thing?

 

[Duetech]

I think I would want both blowers manually switchable. Once you have gasification you could prove it by having the OEM blower working and then reselect for the induced blower. Besides having seen the fire of gasification I'm kind of a junkie and would feel left out or let down just because of some improvement that denies me the visual wonder. Actually until I know that the induced draft blower is working as planned the forced draft will only be idly waiting to be powered up.