Open vs. closed

[wbush]

I've got this 2400 lb. green beast (Greenwood 100) sitting in my driveway about to be installed...or at least put in place under a roof. So I'm talking to "certified" installers right? The first one says that because of over-boiling during loss of AC power, he'd never install anything but an open system with a gravity feed tank above the boiler; no AC power needed to insure that an over-boil is contained. Without it says he, the boiler will generate steam and melt down everything from the pex to the circulator impeller. It won't happen often, but it only takes one time to shut you down and cause 1000's of $ worth of damage. "Why not an AC power backup?", I ask and he says they may work most of the time but eventually the backup won't be there.

The second guy says, a battery and inverter is fine and that he'd never install anything but a closed system because having it pressurized allows higher operating temperatures, greater efficiency, and most of all longer term boiler life because of lower disolved oxygen (less corrosion) due to less make up water and no exposure to the air.

Me, I'm just shaking my head and going crazy here. It seems the open system is a better no-moving-or-powered-parts answer to thermal spikes whether arising from loss of AC power or just the normal cycling of the boiler. But then I don't want to be dealing with a pile of rust in 5 years either.

I need some collective wisdom on this (but if that's not available I'd love to hear from you anyway)!!

 

[Redox]

You are going to want to ask the gurus in the Boiler Room.

Chris

 

[steam man]

My vote is the closed system. If there is a large zone above the boiler it probably can be used as a "dump" zone with an automag valve during power outage. You may be able to install some finned tubing for this purpose. A battery backup certainly can work-I use them in very critical applications at work. They are tested routinely. I would never use PEX near the boiler. It can just get too hot for PEX. At least transition using steel pipe as long as possible before the transition to PEX. You can always put the circulator on the return side subject to lower temps. Make sure the relief valve is placed properly and piped preferably near a drain.

Mike

 

[johnnyb]

burning bush, how would your boiler dude set it up as a closed system, with a heat exchanger or tying direct into your current heating system without a heat exchanger. steam man, what is an automag valve?

 

[steam man]

burning bush, how would your boiler dude set it up as a closed system, with a heat exchanger or tying direct into your current heating system without a heat exchanger. steam man, what is an automag valve?

Automag is just a trade name for a normally "open" solenoid valve with a specific application such as wood boilers. It is open with no power and closed powered. Upon loss of electricity, the automag (piped to gravitate to a zone above the boiler) will open and the hot water will naturally circulate due to the difference in water density. The zone should be large enough to take care of the heat generated by the boiler.

Mike

 

[wbush]

burning bush, how would your boiler dude set it up as a closed system, with a heat exchanger or tying direct into your current heating system without a heat exchanger. steam man, what is an automag valve?

With a hx; apparently not strictly required but done to keep the oil boiler system isolated from the wood boiler system.

 

[wbush]

My vote is the closed system....
Mike

Good thoughts Mike, thanks. Given that there are ways to avoid thermal spikes in the a closed system why do you like closed over open. Is corrosion in open systems a serious problem?
bush