convert longwood forced air chamber to heat water for pex radiant floor heat in slab

[woodwizard]

I am new to site and looking to convert forced air wood burner to heat water for radiant floor. I have used this longwood furnace for 20 yrs. Like furnace but going to radiant floor heat cant afford $ for new stove. It will burn 5 ft logs 10 inchs in dia for 12 hr burn. have area above heat exchanger for 5 ft long and 18inchs wide would like to use tank or coils of tubing to transfer heat from forced air box this furnace has 175*F in forced air box any help or information would be great.

 

[zogger]

Neat project!

I am new to site and looking to convert forced air wood burner to heat water for radiant floor. I have used this longwood furnace for 20 yrs. Like furnace but going to radiant floor heat cant afford $ for new stove. It will burn 5 ft logs 10 inchs in dia for 12 hr burn. have area above heat exchanger for 5 ft long and 18inchs wide tank or coils of tubing any help or information would be great.

I personally can't help you with the design, but I am sure some of the wood boiler guys here will chime in soon. Welcome to the site. We like pics! To get the ball rolling, post pics of what ya got!

 

[HeRoze]

subscribed... i can't wait to see what some have to say on this.

I'm suspecting you're goign to be looking at a pump, a HX, and couplings to your pex. a basic thermostat may be needed as well to cycle the pump. some kind of expansion tank or pressure release in case things get too steamy... maybe some make up liquid....

 

[atlarge54]

Sounds like you're increasing your heat load, since it's tough to retrofit pex in an existing slab. LOTS more information needed. What were you heating before? What will you be heating in the future? Is the slab done yet? etc. etc. etc.

 

[woodwizard]

Sorry hard to write all information down at once I used hot water electric heater to keep floor from freezing last winter no insulation in bldg then now have R30 in walls and ceiling. I have burned wood for 20 yrs in this longwood forced air at my home and still do like stove so well bought another that was like new. I built a bldg 48X36 in middle of 22 acres of woods, poured a slab with 1800 ft of pex in it. Want to use this wood stove has forced air area 5ft long 2ft wide that I want to use coils or build a 50 gal tank to fit inside can get 300 ft of stainless steel 1/2 coil for $300 want some info on what will transfer heat better or any info to make work. I know temp going to slab cant be over 130*F want to warm slab up when there then let elect heater keep it from freezing dont care if it gets down to 40*F it will warm up when I get there and load stove relize will take time to heat slab but will also take time to lose heat could go every three days to load stove. thanks for input will send out pics this week-end

 

[daleeper]

Are you wanting to heat that space solely with radiant heat from slab, or are you wanting to supplement the forced air heat with radiant heat from the furnace?

I would think the longwood furnace would make a lousy boiler. If you are wanting to heat totally with radiant floor heat, get a boiler. However, stealing some of the heat to run through the floor might work.

I'm subscribed and looking forward to seeing this discussion plays out.

 

[atlarge54]

Just to give you an idea of what you may need for heat transfer here's what I'm running. I heat a 1250 sq ft home, insulation is about average, windows not great, plus DHW. I use a modified OWB that was scrapped due to corrosion----the firebox was wrapped with 3/4 inch copper tubing 300' total which was plumbed into a manifold so it is five 60' loops to reduce pump head. After the copper was installed the old water jacket was replaced and the water jacket area was filled with pea gravel to provide thermal mass and prevent short cycling. The boiler feeds about 800' of 1/2" pex in the crawl space floor plus a small water to air HX.

My gut tells me it'd be a challenge to pull enough heat off your stove to heat the slab with the surface area available at your stove.

Please tell me you did put a minimum of 2" high density foam under your slab.

Good luck to ya.

 

[woodwizard]

Are you wanting to heat that space solely with radiant heat from slab, or are you wanting to supplement the forced air heat with radiant heat from the furnace?

I would think the longwood furnace would make a lousy boiler. If you are wanting to heat totally with radiant floor heat, get a boiler. However, stealing some of the heat to run through the floor might work.

I'm subscribed and looking forward to seeing this discussion plays out.

I was thinking of 300 ft of stainless coils inside forced air heat pluem also insulate with boiler insulation the temp inside gets over 180 degrees F it will be on return line all ready got pump from HWH pulling out of HWH into 1800 ft of pex in slab

 

[woodwizard]

Just to give you an idea of what you may need for heat transfer here's what I'm running. I heat a 1250 sq ft home, insulation is about average, windows not great, plus DHW. I use a modified OWB that was scrapped due to corrosion----the firebox was wrapped with 3/4 inch copper tubing 300' total which was plumbed into a manifold so it is five 60' loops to reduce pump head. After the copper was installed the old water jacket was replaced and the water jacket area was filled with pea gravel to provide thermal mass and prevent short cycling. The boiler feeds about 800' of 1/2" pex in the crawl space floor plus a small water to air HX.

My gut tells me it'd be a challenge to pull enough heat off your stove to heat the slab with the surface area available at your stove.

Please tell me you did put a minimum of 2" high density foam under your slab.

Good luck to ya.

Im not wrapping my stainless around anything it will lay 300ft in forced air heat pluem where temp is 180F for hours when burning fire run system last yr with hot water heater need to use wood stove to get slab warmed up I only need 120F to get it up to temp then maintain about 90F in slab.main thing i need to know what type of copper will work with these temps or use SS

 

[HeRoze]

what's a pluem?

 

[HeRoze]

stainless is awful for conductivity... see here: Thermal Conductivity of Metals

i'm thinking copper would be just fine at 180F... it melts close to 2000F.

 

[woodwizard]

stainless is awful for conductivity... see here: Thermal Conductivity of Metals

i'm thinking copper would be just fine at 180F... it melts close to 2000F.

Thanks I will check out sight

 

[kyle1!]

Not much help

WW wants to place a coil of copper or stainless tubing on top of the longwood furnace. The heat from the furnace would heat up the coil and the pump would send the hot water through his pex slab tubing. I assume the coil tubing would sit in the same fashion as an air conditioning coil inside a forced air furnace. Probably a bad idea (bomb?)since it would be closed loop system.

Brian

 

[woodwizard]

D

WW wants to place a coil of copper or stainless tubing on top of the longwood furnace. The heat from the furnace would heat up the coil and the pump would send the hot water through his pex slab tubing. I assume the coil tubing would sit in the same fashion as an air conditioning coil inside a forced air furnace. Probably a bad idea (bomb?)since it would be closed loop system.

Brian

Don't think it can build pressure have 30 psi relief in system plus hot water heater has pop off and its used in system after I pre heat water in stove need information on what would adsorb heat in hot air chamber to pump to HWH thought about SS tank in box and pump water threw it thanks for input

 

[atlarge54]

Im not wrapping my stainless around anything it will lay 300ft in forced air heat pluem where temp is 180F for hours when burning fire run system last yr with hot water heater need to use wood stove to get slab warmed up I only need 120F to get it up to temp then maintain about 90F in slab.main thing i need to know what type of copper will work with these temps or use SS

I wasn't suggesting you wrap anything, just giving you a reference point of the area required to transfer heat.

If you want to heat the water in your floor get a boiler. If you use your longwood to partially heat the water for the slab the building will be a sauna BEFORE the slab even gets warm. Don't fight physics.

 

[dancan]

Image is from Woodstove Water-Heater Coil by Thermo-Bilt, stainless steel, for wood stove, corn stove, coal stove. which I have no experience or association with and there are more manufacturers .
This is a similar setup to what my father had with a Kerr Scotsman which then led into a oil fired hot water furnace .
The coil was made out of copper and was installed in the fire chamber and worked for several years until he got away from wood heat .
Here's another Obtaining Domestic Hot Water (DHW) from a Wood Stove .
I'm sure if this setup works on a stove it should work on a furnace and can't see why it couldn't be adapted to supplement the hot water for your slab .

 

[woodwizard]

Image is from Woodstove Water-Heater Coil by Thermo-Bilt, stainless steel, for wood stove, corn stove, coal stove. which I have no experience or association with and there are more manufacturers .
This is a similar setup to what my father had with a Kerr Scotsman which then led into a oil fired hot water furnace .
The coil was made out of copper and was installed in the fire chamber and worked for several years until he got away from wood heat .
Here's another Obtaining Domestic Hot Water (DHW) from a Wood Stove .
I'm sure if this setup works on a stove it should work on a furnace and can't see why it couldn't be adapted to supplement the hot water for your slab .

Thanks for info I will get pics to you and let ya know how it turns out certain copper tubing has higher temp

 

[dancan]

Glad it shed a little light !

 

[HeRoze]

==== Woodstove Water-Heater Coil by Thermo-Bilt, stainless steel, for wood stove, corn stove, coal stove. === Obtaining Domestic Hot Water (DHW) from a Wood Stove .===

perfect links. the first one has dhw and baseboard apps, and coils as well.

 

[dancan]

Found this one .

Closer to the original question (I think) .

Free Hot Water wood stove furnace Wind power home Solar power how