Masonary Heater with Water Loop

[damdog]

If I add hot water tank valves, to the loop and the lower one would have a pressure relief attached, from there, the hot line 3/4" Pex runs to a 1 to 2 manifold where it splits off and then runs two (1/2" Pex) lines to 14 fin cast iron radiators, the return (cold side) runs to a second manifold where it goes from 2 (1/2" Pex) lines into 1 (3/4" Pex). From here, the cold side has a Tee fitting leading to an expansion tank and the other side continues through a circulation pump, it is then pumped back up to the top side of the loop.

My question is, do you see a concern with pressure in this system? Would the volume of water held be enough to prevent boiling or would you also add a holding tank or chiller line into the mix?

 

[begreen]

One concern would be cooling off the flue gases too much and promoting creosote buildup. A second concern is having a system that is pump dependent in an extended power outage. For sure add a temp/pressure relief valve.

These questions along with a plumbing schematic might be better asked in the boiler room.

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[zak77]

I'd be VERY careful designing your own hydronic system. I thought about that for years but the potential issues always made me think twice about it. I knew a guy who had one professionally installed and i believe one of the pressure reliefs failed to open and caused a steam "explosion" in his basement. No one got hurt and nothing destroyed but it could've been worse. You are basically creating a pressure vessel which can do a lot of damage if not done right. You will definitely need an expansion tank and it may be a good idea to install 2 pressure relief valves just in case one doesnt work. And then you'd need to figure out what to do if you had a power failure, like Begreen mentioned along with possibly cooling exhaust off too much. Or if a pump fails, you'd want a backup because you'll need to keep that water moving and even then you could run the risk of melting the pex, i'd run all copper if it were me.

 

[damdog]

The water loop is directly in the fire box so I do not see and issues with cooling of the exhaust gases. Attached is the drawing of the system.

 

[T-Burner]

I toy with the idea of doing this as well. I work with HVAC hot water loops all the time. Your layout seems fine. Most industrial/commercial systems only have one safety relief valve, by the way. If they fail, they normally fail by leaking, not being stuck closed.

The volume of water in the system isn't the biggest factor to prevent boiling, it's the flow rate through the fire box. I'd size it for a relatively high flow rate, and make darn sure the pump is on 100% of the time your fire is one. The "problem" you have with this setup, is that you can't shut down the fire quickly if your pump stops pumping. Redundant pumps seems like a good idea.

 

[begreen]

DIY Stove Hot Water Systems can explode....

There has been some discussion here about adding domestic hot water capabilities to woodstoves. If you explore this option, make certain you understand the concepts involved...and especially the idea of having a Pressure Releif valve located as close as possible to the store WITH NO VALVES in...

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[kennyp2339]

If your worried about potential pressure due to a power outage or pump failure you can look into a safety loop that runs with the main manifold and is gravity dependent, usually for power outage reasons a zone valve gets wired backwards so it stays closed as long as power is applied, then if no power, it opens up and runs a natural loop usually to a baseboard to shed the heat, just like steam, the cold water comes back (denser) and the cycle repeats. (lots of home engineered in-door woodfired boilers have this safety cushion)

 

[damdog]

I toy with the idea of doing this as well. I work with HVAC hot water loops all the time. Your layout seems fine. Most industrial/commercial systems only have one safety relief valve, by the way. If they fail, they normally fail by leaking, not being stuck closed.

The volume of water in the system isn't the biggest factor to prevent boiling, it's the flow rate through the fire box. I'd size it for a relatively high flow rate, and make darn sure the pump is on 100% of the time your fire is one. The "problem" you have with this setup, is that you can't shut down the fire quickly if your pump stops pumping. Redundant pumps seems like a good idea.

I agree, I actually ordered another pump. I plan on putting it series and will have this power circuit on the standby generator panel.