fireplace used to heat H20 for radient?
| Posted in Energy, Heating & Insulation on
I know that open fireplaces are hugely innefficient. But I was wondering what was out there that could economize the losses by heating water for a radient floor system. This is for a country home so off code suggestions would also be useful. Basically my gal wants a fireplace and I can”t stand them cause of the loss, I like a nice stove, but that ain’t going to happen so any info would be appreciated.
Replies
I was considering the same, using the fireplace as a heat source for radiant heat. Two big downsides.
1. Fireplaces heat at over 400 degrees fahrenheit. Water boils at 212 F. So you can't use water.
2. If you aren't using the fireplace cold air comes down the flue. Say 32 degrees? You can't use water there.
I searched for fluids and found an oil that would work to 600 plus degrees. It was used in industrial applications for heat recovery. It sounded great except that at 30 degrees it became a slushy solid. I couldn't figure how to heat it when it wouldn't move.
Country home-- possibly unheated for a stretch. Most radiant heating has to have a fluid, they freeze. Paper burns ar 451 so it can't boil.
Go with the fireplace and snuggle for warmth. You can't take your money with you. If you really want to be futuristic make a coal fireplace. There is 6 times as much coal as oil in the world.
>> Fireplaces heat at over 400 degrees fahrenheit. Water boils at 212 F. So you can't use water.
So you're telling me the water side on my grandmother's old wood cookstove couldn't possibly have worked? Or the wood fired hot tub heaters I've seen advertised? Or the wood fired radiant floor heater I saw in a magazine?
Most of the time no problem. Some time a problem. Say Christmas morning when you (I do at least) send all the Christmas wrap up in a ball of flame. Dependant on the thermal transfer you could exceed the temp of the fluid in the system if the water didn't circulate. Most of the time no problem. Some time there could be a problem. I've spent more than one holiday fixing stuff that shouldn't clog, break, leak, short, or whatever. I just avoid potential problems. And probably opportunities.Jack of all trades and master of none - you got a problem with that?
Booch,
If you run a open loop system dumping into a holding tank, depending upon the speed of the water you're pushing through your heat exchanger, I can't see how you would have a problem.
Since the water would not be potable anyway, the use of an antifreeze solution (which also works on the high temp problem) makes sense.
But there are bigger problems. The water jacket needs to be custom made. The angled sides to a fireplace thereby require mitering (sawing) of the relatively thick steel walls prior to welding. The quality of the welding itself becomes critical since you got no possiblity of being able to pull the unit for repairs. The high temps you mention, coupled with unknown potential caustic reactions, will cause the steel to burn away over time, thus limiting the timelength of its function.
It will have to be carefully designed and installed appropriately. Checks and balances need to be designed in. It needs to be overengineered.
Bottomline, the concept has merit, but you better know what you're doing and expect it to cost far more than you'll ever get out of it.
Cost to implement it safely is what I see as the biggest hurdle.
I have a friend who has a system he designed into his house. He has a wood stove with a standing chimney behind it. The chimney has loops of pex running through it which go to a heat sink holding tank under his garage slab. In the sand surronding that tank is more tubing to reclaim the heat and circulate it through three zones of the house on demand. He has backyup but I'm not sure if it is a hot water heater or an oil boiler Once the system is fired up and warm, the house can stay warm for three days in 30-40° weather. It's comfortable, even heat. He also finished a room over the garage for his wifes crafts and hasn't needed to install additional heat up there. He can work on the floor of the garage without getting cranky because the heat makes the crete feel almost soft. From what I can tell, it's a working system that heats a very large (probably over 4000 sf ) house.
Downside - he's married to it, hauling wood to fire the wood stove to keep the chimney mass heated, and he seems to be always fiddling with it - maybe 'cause he's a natural born fiddler - but he says that he probably wouldn't do it again. Too costly for fittings and parts and planning for what it gives him, and because it's a unique system, it could harm resale value of the house.
There are other similar things like the external Hasha units with a water jacket surronding the firebox. I can see it happenning but at greater cost than you first anticipate, as all prototypes are. And cost savings is the goal here, right? Better to let her heat you!.
Excellence is its own reward!
About 25 years ago there were some hydronic inserts on the market that ended up with severe problems. Steam explosions!!
What you are looking at is essentially a custom boiler with all of the controls, water level, pressure, flow switches etc. associated. A year ago I was asked to design one for a house in Telluride. I submitted a design proposal for $18,000 half of which was for liability coverage.
The open tank idea has merit and has been used in combination with drain down solar systems. Major problems can develop if iron fitted pumps and valves are used. Some ended up creating steam baths in the mechanical room because of overheating. One had a truck radiator outside to reject excess heat!!
Except for the can't use water comment, previous comments are helpful.
Have a DIY built water wall fireplace myself, heated a 5300 sq ft house with it alone for 33 years.
Uses a 1/3 HP Bell/Gosset circ. pump, drives water thru both fireplace and radiant pipe loops and old car Air Cond condensor coils in forced air system, also preheats water to HW heater. FP has closed doors (used to be tempered glass, got dirty so quick went to steel doors with cutouts-see attachment - look close and you can see torched out silouettes welded back in place, quickest pix I could find in files)
Anything in the ashes should be stainless steel pipe unless you want to replace pipes every few years. A good damper is a must for economy.
David in Alaska has posted he has installed a few similar systems for friends with good success, check the archives.
Happy it works for you. Water could be great but as a guy who sees the dark side of design flaws I'd think in terms of "no electrical power, heat is off for 3 days, and my idiot (nephew, husband,wife, tennant, fill in the blank) is running the fireplace"
I do concur on the SS tubing wrapped around the flue / firebox. great method to get the energy out. The fluid is my only concern.Jack of all trades and master of none - you got a problem with that?
Patrick,
I suggest you look at Masonary Heaters as an alternative to a conventional fireplace. I've recently completed a project with one and I love it. It's much more that "just a fireplace". These babies put out some serious heat, depending on the wood load and how frequently they are fired. It's not impossible to get 25,000 btu/hr out of a well designed project. They also have option for bake ovens.
I've also seen and read about heaters that have stainless steel hot water coils in the back of the firebox that can be hook up to a hot water storage tank. This might be practical with the radiant floor heat you mentioned.
Check out this website: http://www.mha-net.org/msb/index.htm Lots of great info and pictures.
Good luck.
Tim