where are the problems in having a outside forced air system ? what would be the benifit of heating water without storage , transfering the water to a hx and turning it back into forced air ?/
why not forced air
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Nofossil
Moderator Emeritus
joe2003 said:
It's a lot easier to move a given amount of heat stored in water than it is when the heat is stored in air. A gallon of water with a 20 degree temperature drop delivers 166 BTU. It would take over 500 cubic feet of air to do the same.
When I have considered different heating systems, here are the reasons I didn't consider outside forced air systems, and the reason I cringe when I see one installed. That hot furnace is setting right along the side of the house, and usually not as much attention is paid to keeping that area clean like you would if that furnace or stove was inside the house. I know this isn't fair to those that are burning them properly, but I usually see a lot of creosote buildup on the chimneys and on the side of the house because they have not installed a tall enough chimney. A water system can be installed farther from the house with less heat loss. It looks to me like it would be easier to insulate the water pipes than it is to insulate air ducts. Most of the installs of forced air usually are just stuck in a window instead of tied into the central heat duct system for less than ideal air circulation. Water will come into the house through a smaller hole than forced air, and can bend corners easily.
Benefits of water would be that there are more options in heat transfer. Not only can you simply use a heat exchanger in your current air handler, you might also use it in domestic hot water system, radiant floor heat, baseboard heat once you have the hot water. Zones would be easier to set up than with forced air.
I would be interested in seeing photos and/or descriptions of good outside forced air systems that work well. I know my cousin has one, and likes it. He has moved it 2 or 3 times, which would be easier with this type unit running through a window. As a landlord, I don't know if I would allow one. I have a neighbor that has a wood furnace inside, and is getting one to move the mess outside. Some insurance companies demand an outside wood heat unit be so many feet from the house, might be a problem for the forced air type.
Benefits of water would be that there are more options in heat transfer. Not only can you simply use a heat exchanger in your current air handler, you might also use it in domestic hot water system, radiant floor heat, baseboard heat once you have the hot water. Zones would be easier to set up than with forced air.
I would be interested in seeing photos and/or descriptions of good outside forced air systems that work well. I know my cousin has one, and likes it. He has moved it 2 or 3 times, which would be easier with this type unit running through a window. As a landlord, I don't know if I would allow one. I have a neighbor that has a wood furnace inside, and is getting one to move the mess outside. Some insurance companies demand an outside wood heat unit be so many feet from the house, might be a problem for the forced air type.
my concern is if i store the btus in the water and use a water to air exchanger i can only collect the heat at certain temps. between 190 and 120 correct? 120 being a low point and not sure how much heat i can pull of that . ? then when you figure the recovery time . wouldnt less effort be put into it just forcing air instead of putting it into water and then back to air? reason im going into this thought process is im not sure on the water tight welds being ill be the one fabricating the burner . The outside forced air units ive seen look just like a owb except no water and air supplies.
here are 2 links.
http://www.dynamitebuys.com/store/cart.php?m=product_detail&p=1859
http://www.charmaster.com/embers.html
here are 2 links.
http://www.dynamitebuys.com/store/cart.php?m=product_detail&p=1859
http://www.charmaster.com/embers.html
Nofossil
Moderator Emeritus
I don't work with hot air systems, but the numbers don't seem to make sense to me. I looked at the first link. A 200,000 BTU per hour boiler would need a LOT of air to move that much heat. Even if you plan for a 100 degree delta T, you'd need over 2000 cubic feet of air per minute. That seems a bit much for a 10" duct - works out to something like 65 feet per second air velocity.
ewdudley
Minister of Fire
joe2003 said:
For a water-to-air HX if you need 140F water, that's what you need, and the boiler controls are set up to do that. It's not necessarily significantly less efficient, especially since when burning solid fuels you need fairly hot combustion surfaces and flue temperatures in any event.
All you need to decide is if the advantages of one over the other make more sense for you in your situation.
If you've got house that could take advantage of an outside forced-air unit that sure would be simple and economical way to go, especially if you had a back-up system that could take over when it wasn't convenient to tend a fire.
I saw a nicely done one where the guy poured a small slab out of the way on the back side of the house. He said what really made it work for him was that he ran a duct through the basement to the far side of the house for return air. Supply air was a single duct into the living room, but the house was compact so it worked well.
Here's another one:
http://www.outsidewoodheater.com/id1.html
--ewd
joe2003 said:
If you are worried about the welds forget it because if the welds leak air they will leak co2 and that will KILL you. Thats why you hear people dying as there heat ex got a hole in it and the co2 goes right into the house. Hot air furnaces will kill, boilers will leak water but you won't drown.
leaddog
Hunderliggur
Minister of Fire
Actually, the CO (carbon Monoxide) will kill you. The CO2 will just kill the environment or feed the plants depending on you views ;-)
the fire chamber wouldnt need any interior welds except the flue . so the co wouldnt be much of a issue , to go with forced air a person could use a tank of some sort for the fore chamber. right? now why do you suppose forced air unit require thinner steel for the fire box how can these unit get away with it ?
just to let everyone know i would love a boiler and ive set out to build a garn alike. I guess thats where the water tight welds come into the pic . there sure are alot of welds in that unit..... hell, i already got 90% of the matterial gatherd up. 36 in gas line 30 in long, 1/4 in steel, 5 1/2 90s , 5 1/2 in steel pipe , and other odds and ends i havent came up with the tank yet but ive been trying like hell . I did find one that i could get for 100.00 but the ends are rusted out . I do have a 1000 gal drum that i could build a owb but not being to eff. made me wonder if i were going to go that way why not just do forced air
just to let everyone know i would love a boiler and ive set out to build a garn alike. I guess thats where the water tight welds come into the pic . there sure are alot of welds in that unit..... hell, i already got 90% of the matterial gatherd up. 36 in gas line 30 in long, 1/4 in steel, 5 1/2 90s , 5 1/2 in steel pipe , and other odds and ends i havent came up with the tank yet but ive been trying like hell . I did find one that i could get for 100.00 but the ends are rusted out . I do have a 1000 gal drum that i could build a owb but not being to eff. made me wonder if i were going to go that way why not just do forced air
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