Utilizing Existing Furnace Convection System...

[Peter B.]

Hello:

A friend is planning to buy some sort of outdoor furnace system before winter. I'd been hoping I could talk him into a gasifier and storage, but it looks like he'll be going for a Central Boiler CL 5036 from a local dealer with a decent reputation.

I'm wondering whether Central Boiler itself is considered a quality manufacturer... and whether the '25 year warranty' means much... even assuming they're still in business in 25 years.

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.

I'm thinking that *maybe* putting an 'oversized' water to air heat exchanger coil right below the original floor grate (from the furnace shroud) might work for him... and take advantage of the existing convection system.

Does this seem like a plausible idea, or should he plan on multiple radiators or baseboard units?

What think any of you?

I'm also hoping to help him work out a basic plan for the water delivery system, but have a lot of learning to do. I wonder if someone could point me to a bare basics diagram of what's required?

Thanks for any and all replies.

Peter B.

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[pybyr]

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

(broken link removed to 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

 

[micifus]

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.

 

[Redox]

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

 

[pybyr]

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"

 

[Redox]

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"

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

 

[pybyr]

[

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

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

 

[BrownianHeatingTech]

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.

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.

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

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.]

Hey, thank you all for the replies and suggestions... gives me some additional ideas to think about.

I will have to do some extensive scoping of what would actually be involved in using the space below the grate. pybyr may be right... the guts of the furnace may have to come out.

Right now we're just in the brainstorming phase and I don't know what my friend will finally decide. The way things usually go is I try to steer him one way and he heads off in another direction... so maybe if I don't suggest anything to him he'll arrive at one of these ideas on his own.

At the moment, I think he's trying to locate some iron radiators.

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.

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[GARYL]

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.

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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