In our country home, I need to move warm air produced from a wood stove horizontally through my house remodel project. Has anyone built a heat ventilation system using convention ductwork with an in-line fan? The stove will be in a high ceiling room (20’ x 18’), 3/12-pitched to about 12 feet to the peak. I figure the stove to produce more heat than needed for the room, and that heat will rise to the top where it can be sucked into a high intake vent, downward for 4 feet and then horizontal for about 18 feet with a terminal exhaust vent and possibly a midway vent. There will be a large (5’ x 7’) opening between the adjoining spaces for convection return.
Will this work? Any ideas or rules of thumb to consider? Recommended sizes for vent ducts and fan?
By the way, since wood heat is central in nature, I intend to modulate cold spots in various spaces in this project by placing electric baseboard heaters on multiple thermostats to fine tune heating. I figure electric heat competes in price to propane for BTU output. Wondering what the carbon footprints are for those two sources as back-up heat? At least electric seems to have a potential future as environmentally clean energy.
Replies
I met a couple that place an air return at the top of the vaulted ceiling in their great room and built a fire in the fireplace at night and turned the hvac fan on at night to recirculate the rising heat throughout their house as they slept. With a well sealed house this system was very effective.
I have a friend who has done kinda what you are talking about - he has an intake high in his wood heated great room - the heated air is circulated down under the floor and distributed by ductwork to other spaces surrounding this big central space - he uses the squirrel cage blower associated with a (now defunct) forced air furnace
works well for him and with the warm air under the floor, even that is warm -
I've heated exclusively with wood for 30+ years - a ceiling fan will circulate heated air pretty well on it's own, and I'd advise you to consider one for both winter and summer use - my experience is cold floors are the worst aspect in my situation
seems like in your situation the quietness of the circulating fan is very important - which suggests slow speed/larger is better - my gut feeling is it isn't going to take much capacity to do what you want to do - where are you located? are you going to be dealing with -20*F for long periods of time each winter?
one other thing my friend has is a little pistol shaped thermometer that he can point at the intake and then the outlet and see the temp differences - point it anywhere and see where the hot spots and cold spots are - neat item and only about $40 - -
David,Thanks for the reply and advice. We live in southern Wisconsin, with winter temps dipping to sub-zero every year. The project is turning a vacated shop and garage on the lower level to living space. We have been living upstairs above the garage, heated by a propane forced air furnace (not large enough for the additional space). We also have a small woodstove up there that heats the space easily with little wood. The house will be well-insulated and tight throughout.What do you think about using regular forced air ductwork, especially sizing?Joe
In our last house we had a wood heater in the basement next to the furnace.
The wood heat had two fans. One blew/sucked cool return air from the house return ducts over the heater box.
The other was thermostatically controlled and would blow on the fire. So when the temps dropped in the house this fan would light up the fire box. Otherwise you just had a lazy fire.
The heater just had a couple of ducts that bypassed the furnace. You did have to have the furnace fan on all the time though.
Another thing was that if you let the fire die down the house furnace automatically kicked in.
It had a large fire box you could stuff full that would last quite a while.
This system used the existing ductwork to distribute the heat.
One shortcoming was getting all the wood down to the basement. If we stayed there and I had the gumption, I would have liked to have built a wood chute like the ones they had for coal. Ya, I said gumption.
I did something similar once for a friend. I just took heat out of the stove room ... I think at floor level and put it in another room using a salvaged centrifugal fan and standard ductwork. I think I had a sheet metal guy make up a box/plenum for it. I provided a simple switch in her hallway for easy access to use it as she saw fit.
Personally, and as a GENERAL statement, I'd never use/recommend electric resistance for heating ... even from a 'clean' source like e.g. PV or wind. If you are using wood heat from a local source (like your property or other very convenient source) and season and burn it properly, you really can't beat that.
Thanks. I agree with you about using local wood source heat. I want to put the electric in as a back-up for minimal heat when away from home to keep pipes from freezing and to boost up small areas that tend to get colder when such a central heat source as wood is used. The better my air movement system works, the less I should have to depend on electric. I would not consider electric except that its alternative is propane, about the same price per BTU.
Elegant Solution-
We installed an RSF Opel wood-burning stove and chose it over the other brands because it had a solution to this problem. Ours is set up to heat downstairs and upstairs from the floor that the fireplace is on. This one has a "gravity vent" which is just hot air moving up a duct by normal convection to upstairs. The other is thermostatically-controlled. When a dedicated thermostat in the fireplace room reaches the set temperature, it kicks on a blower that will dump hot air to the floor below (or wherever you duct it to). I think it's a neat system.
http://www.icc-rsf.com/en/rsf/The_Opel_2_fireplace
http://www.icc-rsf.com/en/rsf/Heating_Performance_Options
Johnny
I'm with David Doud in thinking that low speed air flow would be better than high speed. Noise would definitely be a consideration too.
If you can take the air down under the floor you'll get a bit of radiant heat, and that can be helpful. That works particularly well if ya have a basement.
I tried the big return duct up at the ridge solution, but wasn't happy with the results. Too much hot air stayed put, and what did get ingested didn't seem to make any difference at the extremities of the house.
This year I installed an up-draft ceiling fan over the stove which creates a large cyclic flow of air. It's made a big difference. You no longer walk into a wall of hot air on the upper floor, and the main floor is heated more evenly.
Scott.
Scott,Did the up-draft ceiling fan improve the performance of the blower/vent system, or did it replace it?How far were you dropping the ductwork from the ridge, how did you turn it horizontal, and how far did you run it horizontal?How many exit vents or diffusers along the horizontal?How many cfm's in the blower fan?Thanks,Joe
>>>Did the up-draft ceiling fan improve the performance of the blower/vent system, or did it replace it?The return intake is still there, and we run the furnace fan 24/7, so I would say that the ceiling fan is "in addition to" the forced air network. Like I said though, the forced air solution didn't really work that well for me.>>>How far were you dropping the ductwork from the ridge, how did you turn it horizontal, and how far did you run it horizontal?My return air intake is simply mounted in a wall that reaches up to the ridge. Kind of hard to explain. Let me know if a pic would help. The ridge is at right angle to this wall; I didn't extend the ducting horizontally at all.>>>How many exit vents or diffusers along the horizontal?It's a whole-house forced air network with about forty outlets.>>>How many cfm's in the blower fan?You mean the ceiling fan? I think it's rated at 23,000 CFM, but at max speed it's quite noisy and moves way too much air. It's just a simple commercial unit that cost less than $100. We run it at the second-lowest setting and it moves plenty of air with no noise.Scott.
I was contemplating the same type of system you describe. I have a wood stove in a central great room and thought about sending the trapped hot air from the ceiling ridge level down to the basement.Woodstove is supplemental to whole house in-floor hydronic heat upstairs and down so I hated to add a forced air system of any kind and mess up the radiant by introducing convection currents and stratification of the airspace.I figured it wasn't worth the effort to try to "recycle" the ceiling heat but it may pay off to switch the fan to bring cooler air in from the basement in the summertime.How big does the fan and ductwork need to be to move enough CFM without creating a wind tunnel? Is it worth all the effort in your opinion after living with basically the same situation?
>>>How big does the fan and ductwork need to be to move enough CFM without creating a wind tunnel? Is it worth all the effort in your opinion after living with basically the same situation?My experience doesn't support the idea of distributing heat via ductwork. Quite the opposite, the updraft ceiling fan has done a much better job than the return air intake at the ridge.Every house is different though, your mileage may vary.Scott.
I think I am talking about something slightly different than collecting heat at the ridge of a cathedral ceiling and then sending it through an entire forced-air ductwork system. I am trying to collect it and send it through a short, dedicated ductwork system with a total run of about 25 feet (6 feet down and 19 feet horizontal), with one or two exits along the horizontal.
>>>I think I am talking about something slightly differentYes, I began to think so. It might be plausible, but be careful of fire code issues, especially if you plan to have it inspected. There are reasons why you don't see any sort of heat collection apparatus on wood stoves.Good luck with the project, and please let us know how it works!Scott.