Utilizing Existing Furnace Convection System...

neat question- neat thing that you and your friend are attempting

as I understand it, the water to air "car radiator type" heat exchangers tend to be designed around the assumption that there'll be a fan to (a) push a lot of cubic feet of air per minute through their tiny openings between the fins (need to move a lot of air, and fast, to pull that much heat out of the relatively small coils' tubes); and (b) overcome the resistance to airflow resulting from the fact that you only have a lot of tiny openings between the fins and coils

gravity air systems basically depend on relatively big wide-open ducts- so you basically need something that can put out a lot of heat but still let air through with as little air resistance as possible

I was looking into an interesting product that's meant for ceiling heaters in commercial spaces, though I was thinking of it for a dump zone

http://www.heatinnovations.com/ceiling-heat.htm

I called the manufacturer and they quoted me about 1300 for the whole unit, and were willing to sell the spiral coil alone for around 800

if you could put a coil like that in/directly under the huge grate, it would actually act sort of like a radiant floor (though in a concentrated spot) and I think would let the natural convection air flow through better than a "modern" tube & fin water to air heat exchanger.

or build your own large-diameter/ low air restriction "big water coil" down under the center grate

for piping, start with the stickies at the top of this forum- read and digest all the stuff in those, and then you'll be ready to start asking the people around here that really know this stuff bunches of annoying questions-- just like I do

Does the return system have an air filter on it? Most people use those crappy blue fiber ones. You can spend a little more money on a better filter to help reduce the dust in the house.

Also out of curiosity how much are you paying for the 5036? I am doing some price research in my area and am wondering what people are paying for these units new.

Ya, I don't think you are going to get the circulation out of it, unless you are making steam, and even then...

Baseboard isn't too hard to install and would work a lot better.

Chris

what if you removed the guts of the original wood gravity furnace, then took a 55 gallon drum and used a "deheader" to take the top and bottom out of it so it became a large diameter steel tube. then wrap a whole bunch of pipe around it for your heat exchange from the OWB, and set the whole thing inside the old gravity furnace's box/ plenum, elevated on some legs, so that air could convect up both the inside and outside of this big heat exchange drum.

use a muffin fan in the middle of it to give a mild "boost" to the convection if you need to

I can make no guarantees this'll work- just trying to help "brainstorm"

pybyr said:

what if you removed the guts of the original wood gravity furnace, then took a 55 gallon drum and used a "deheader" to take the top and bottom out of it so it became a large diameter steel tube. then wrap a whole bunch of pipe around it for your heat exchange from the OWB, and set the whole thing inside the old gravity furnace's box/ plenum, elevated on some legs, so that air could convect up both the inside and outside of this big heat exchange drum.

use a muffin fan in the middle of it to give a mild "boost" to the convection if you need to

I can make no guarantees this'll work- just trying to help "brainstorm"

Click to expand...

Hmm, the chimney effect. I like it! Maybe two barrels stacked to amplify the effect? It would be better than a finned heat exchanger at creating a draft.

Chris

Redox said:

[

Hmm, the chimney effect. I like it! Maybe two barrels stacked to amplify the effect? It would be better than a finned heat exchanger at creating a draft.

Chris

Click to expand...

Yep- that's what I was thinking- it's sort of the same principle these old gravity-air furnaces worked on in the first place

you'd want to be very sure to plumb it in a way where the hottest water starts at the top of the "barrel coil chimney" and the cooler water returns off the bottom- so as to maximize the draft and also the most efficient transfer of heat from the water medium to the air medium

if you lacked the vertical height to stack two barrels like Chris mentioned, you could maybe do two concentric "barrel coil chimneys" with a tube made from a 35 gallon drum inside one made with a 55. you'd want to build and orient them so that there is some significant space for air to rise between each of the layers from inside to outside

I suppose if you had some other way to give structural support to tall coils of pipe, there'd be nothing magic about using old metal barrels- I was just trying to think of something already available and not expensive

Peter B. said:

My friend has an older farmhouse, and he's been heating with the original built-in wood furnace which is hooded with a convection shroud. The sole source of heat is through a large grate in the living room floor (ducted directly from the shroud). There are cold air returns throughout the house, but no (additional) hot air ducting. With a good fire burning, the convection system works well without use of a fan.

And, because of breathing problems (and a dusty house), my friend doesn't want to use a fan unless absolutely necessary.

Click to expand...

Personally, I'd recommend baseboards or radiators for that application.

Hooking up a hydro-air unit (with fan) and ducting it into the house properly would not be too hard in most cases. Add a quality filter, and it will reduce the dust level in the house.

I'd suggest looking into reversing the flow, so that the central supply becomes the return, and the multiple returns become the new supply registers. You may need to find a local HVAC contractor to determine if that is practical or not.

pybyr said:

I suppose if you had some other way to give structural support to tall coils of pipe, there'd be nothing magic about using old metal barrels- I was just trying to think of something already available and not expensive

Click to expand...

Skip the barrels, and solder some straight pieces of copper to the coils, to support them. Soft copper comes pre-coiled, so just be careful with it, and it should be fine.

Joe

Peter B. said:

Another couple of questions: a) Are old oil tanks (250 gallon) frowned on for use as additional storage? b) If not, any recommendations for effectively flushing them before use?

Thanks Again.

Peter B.

-----

Click to expand...

Peter B.,
I used two 275 gallon oil tanks for over 20 years and they worked great. I bought mine new so I didn't have to deal with the cleaning of them. I hit up every garage in a 20 mile radius for the antifreeze from cars that was flushed from the cooling system. Radiator flushes aren't done much anymore so that source has dried up.

With 550 gallons of used antifreeze and some rust inhibitors the tanks never had a problem. I never had a filter on the system and my pump never got plugged. I used a ball vent and vented to the outside so as not to get the antifreeze smell in the house. In 2001 I stopped burning wood and gave them to someone who is still using them today.

I'm sure stainless or a lined tank is the preferred method today.

Hope that helps.

Good luck,
Gary