i don't know enough

[Deleted User]

to know if i'm asking the question correctly but, i was told that if i installed a properly sized water coil in the heating duct of my fireplace/furnace, at 9gpm i would get a constant supply of 140deg water(approx 86k btu/hr) and that would allow me to adequately heat 1200sqft of floor space in my home, roughly 1500ft of 1/2in pex.

JimGPE_2

Ho boy.

No one is responding, so I, the non-expert in matters hydronic will weigh in.

If I understand you correctly, you want to put a coil in your fire place and one in your furnace, with water piped between.

I would REALLY recommend against this! With all due respect, this has flaming disaster written all over it.

The big question is what happens when the coil gets more heat from the fire than the furnace or PEX can dissapate? What happens when the fire place is burning but nothing is calling for heat? With a boiler, the op stat kills the fire. If that fails, the limit kills it. Failing that, the pop-off valve kicks, spraying live steam all over the basement.

There's no way to kill the fire here. Excess heat changes the water to steam, then increases the steam pressure until something fails with a sizeable bang.

This is a scary idea. There's live steam or an exploding piping system in your future.

Am I missing something here?

Art Pittaway

Okay, I'll try,

It's actually a good idea...BUT, the "coil" in the fireplace has to withstand the high temps it will encounter. The water will certainly turn to steam if it isn't circulated, but if you can pump to a storage tank and through the furnace coil you will save the btu's for when the fire goes out. Now, how big does the tank need to be? How about several electric water heaters (no electric). How big is the furnace coil? The fireplace should be black iron pipe, galvanized will give off toxic fumes.
Or, if you have lots of wood and time and want to buy something that works, look up wood burning boilers and there is a company in Minn. that makes a very nice unit. Looks like a shed in the yard with a chimney, and they work very well. Can't think of the name but someone will.
Whatever you do if it is to work it will take a lot of study and planning, and won't be cheap if it's right.

[Deleted User]

fireplace/furnace

thanks for the prompt reply and the term fireplace/furnace misunderstood you.

i've been heating my 1800sqft home with a wood-burning, fireplace/furnace(just a term) for the past 7yrs.
it heats via forced-air or convection.

i've been told by the manufacturer, that an appropriately sized water-coil placed inside the 'ducted' area of the fireplace, will allow me to blow 140deg air(85k btu/hr) across the coil when the blower is on. therefore, using the coil in that manner i can simply attach a circulating pump from the coil to my 1500+ft, parallel circuits of stapled-up pex and heat my floor. the flooring is oak, ceramic tile or linoleum over a 3/4" plywood subfloor.
considering 140degs, there is no need for an expansion tank, mixing valves etc and it's only a matter of circulating the liquid.

i don't know much but i find it hard to believe that the coil could extract enough heat to do the job.

billygoat22

I helped pull out a system, 1970's vintage, that also had a coil in the fireplace. I don't recall how they wired the controls, but the core of the system was a 1000 gal tank in the yard. I assume water circulated constantly while fire burned to dump heat in the storage tank, so water temp didn't rise in piping and coil. All the piping was copper.

Dan Law

Terminology

I don't have the answer your looking for, but I think I can offer some clarity for others reading this question, if I understand you correctly. We need to change some terms.
He's asking about placing a finned coil in the supply duct from his wood fired furnace, and series piping this coil to his radiant floor. The "fireplace" coil is not going into his firebox or the flue passages of the wood fired furnace.
He expects the maximum temperature available to the coil inlet air side to be 140F (70F rise across the wood fired unit's heat exchanger). Seem to me this sounds reasonably safe (if that term even applies to wood fired units) so far as overheating or over pressurizing the hydronic loop. Regardless Mike, whatever you do, the loop should include an expansion tank and a relief valve. How much heat you'll get is dependant on the wood furnace capacity, the air volume and velocity, and of course the fire. Remember Mike, heat quantity is measured in btuh - not just degrees F.
Maybe someone from the solid fuel biz can help him out.

[Deleted User]

pumping

is one of the chief issues.
during power outages, i'm guessing that i'd need a 12v backup pump or a generator to avoid excessive temps with the water coil in a 212+ temp environment.
that's why the manufacturer advises putting the water coil in the duct. the temp doesn't go above 140 and in the event of a power outage, it wouldn't matter that the circ pump isn't running.

[Deleted User]

i follow

the manufacturer says that a 9gal/min pump, incomming air at 1400cfm, output temp of 140, approx 86k btu/hr will transfer to the water.
1/2in tube, 3 coil unit that's 27x22x3-3/4

eddie grierson_3

Thoughts

I understand what you are trying to due. I would make sure you have backflow preventer if you have this connected to you domestic water. Like the other guys said you will also need a releif valve and expansion tank at the minimum. I would ask the manufacturer for a piping schematic. As far as the Btu storage tank goes it would be a plus, but if you get into all of that you probably should have got a boiler.

[Deleted User]

boiler

i do have an uninstalled boiler and plan to use it in
the conventional manner but i'm also trying to learn all the angles.

i really do appreciate all the input from you guys.