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[Scott7m]

Why not?  I've recently been looking into selling a line of pressurized indoor boilers.  With a pressurized system they do not even treat there water because as a closed system no oxygen is present.  So what would be the trouble with running my owb at let's say 5-10# of pressure and have a pop off valve for safety.

Oil and gas boilers have been made like this forever, some ppl freak when they hear pressurized but heck you have a hot water heater in your house now that's under much more pressure than I would run my stove at.....
 
What do you guys think?

[Critrgitr]

I'm no expert by any means, but I do work at a powerplant and have a fair amount of experience with pressurized systems. I'd have to look at the temperature curve in regards to the kind of pressure you're talking about, but if I had to guess I'd say that many of a non-pressurized systems components may not be rated for that kind of temperature. I would also find it hard to believe that a pressurized system wouldn't have to be treated.........the extra temperature and pressure have affects on components that you wouldn't normally see on a non-pressurized system. Normal PEX tubing may not be rated for those temperatures, although that is just a guess. In essence, your non-pressurized system is in fact pressurized to a point. Your pump discharge creates a certain amount of PSI since it has to flow through a constricted passage ( i.e. HX and tubing ). There would be many things to look at in regards to the amount of PSI the components were desinged for. Five to ten PSI doesnt' sound like much, but in order to achieve that much pressure your water temperature would probably be running in the neighborhood of 220-230 degrees ( just a guess ) maybe more. Have the wrong piece of equipment fail, or loosen the wrong clamp and you'll be in for a serious instant burn. I'm not saying the system wouldn't or doesn't work, but I think there would be a-lot more safety issues involved with them compared to a NP system.

[Scott7m]

Pex tubing is rated at 180 degrees with 100psi. 

Gas boilers are pressurized and don't go up that high in temp, i wasn't going to run it hotter than I do now just wanting to pressurize for longevity.  Heat exchangers I used are tested at 750psi. 

European style gassers last well over 25 years and most don't use treatment. 

[mcarter]

Can you pressurize a system made of stainless steel?

[Critrgitr]

I'm probably not thinking of this correctly, but unless you raise the temperature of your OWB tank, how would you maintain 5-10 psi? If you filled your OWB completely and removed any air from the system your pump(s) would create a supply pressure as well as a return pressure back at your boiler, but without maintaining a void of space at the top of your OWB tank I'm not sure how you'd allow for any expansion or contraction of your water level when your boiler cycles in temperature.

[Scott7m]

I'm probably not thinking of this correctly, but unless you raise the temperature of your OWB tank, how would you maintain 5-10 psi? If you filled your OWB completely and removed any air from the system your pump(s) would create a supply pressure as well as a return pressure back at your boiler, but without maintaining a void of space at the top of your OWB tank I'm not sure how you'd allow for any expansion or contraction of your water level when your boiler cycles in temperature.

An expansion tank, like the ones on your water heaters.  My dad has ome with an expansion tank on it, but it's running off of a pellet stove, he installed a 16x18 coil in front of the fan on the pellet stove and then ran it to a hot water tank for storage then on to another building where another 16x18 is located.  It keeps that 1400 sq ft shop about 60 and his main garage about 65-70 using a magic heater on the exhaust, thats on the setting of 4, if he runs it up on high it will make his main garage 75 or more and the separate shop the same

[RSI]

You don't want to pressurize a boiler that wasn't designed for it. Any flat surfaces will start bowing out pretty fast. The back wall of the firebox and waterjacket on your a would probably be the first to go.

Also, if you have it pressurized and something goes wrong like you forget the ash drawer part way open, the relief valve isn't enough to be safe. You have to have a dump zone otherwise something could blow up.

I am not sure how many other states require it but most of the indoor pressurized boilers require a certification here or aren't legal to sell / install.

I would just keep the recommended chemicals in it and forget about it.

[Scott7m]

Yea those were my concerns about even running just a bit of pressure. 

[MattyNH]

My outdoor wood boiler is pressurized..Runs the same pressure as my indoor wood boiler (10-15 psi) On the wood wood boiler is has a temp relief valve, pressure relief valve..and It has a dump zone that is hook into the control box at the oil boiler So it will dump the heat upstairs in my house.....Plus you have all the relief valves at the oil boiler....Because its a sealed system no use of heat exchangers, (unless hot air) no adding chemicals to keep oxygen out, No need to add water, no mineral build up.
Back in 2008 New Hampshire had a massive ice storm..I had no power for 32 hrs..Now on that note I had a live fire in my wood boiler.The temp. relief valve popped like its designed to do.. Never had a problem with my OWB and its been 5 yrs..

[Sconnieman]

I've got basically the same boiler as MattyNH except mine is hooked to a forced air furnace instead of an oil boiler. Pressurized wood boilers have been used for years. People have been using HS-Tarm indoor pressurized wood boiler's since the 70's. I had people telling me to stay away from pressurized systems because they are finicky, but I've been running mine for a few months now without any problems. You are supposed to use oxygen barrier pex instead of regular pex, but it doesn't cost much more anyway. I've found there are two things you need with a pressurized system that might not be as big a deal with a non pressurized system. They are good temperature control, and high point relief valves. There is no "boiling over" with a pressurized system so getting the firebox air tight is important. Basically if your water gets too hot the pressure rises and the pressure relief valve pops, and causes a big mess on the floor, then your temp relief valve pops and causes more of a mess. I didn't have this problem but a friend did. His boiler is in his garage and he had a nice ice skating rink in there for a few days. To put it simply, auto dampers are a must have. High point relief valves are simple little things that work like magic. When you first fill your system there will be a little air trapped in the lines. I have a manual valve on both of my pex lines at their highest point. The air collects there, I can literally hear the air in the lines. I crack the valve open, it hisses a little then I close it and repeat until I can't hear the air anymore. Did that once when I filled it and it has worked ever since.

[willieG]

i agree ther is nothing wrong with an indoor or outdoor wood boiler under pressure if the said boiler is designed and stamped and tested and approved.  Yes they have bee around a long time, i used to stay at a friends grandparents over 50 years agon and he was a plumber by trade. He had a wood boiler in his garaged that was pressurized and used fin tube baseboard rads.

a lot of us here on this forum have bought this non pressurized system to keep the fire outdoors and like the idea of no fire in the house anymore and with that the comfort of no pressure because ill bet there are some here that don't even think about their water system as being a "pressurized system"

one of the main reasons these stoves likely came about is anyone can build them, there is no governing (well was none) agency that could prevent you from building your own as long as it was not a "pressure vessel"

with a pressure vessel comes (i would think?) mandatory testing every so many years (another cost) that most of us would likley prefer to stay away from

you get a leak in the pressurized boiler, it is (here in canada anyway) only a certified pressure welder that can weld it, tested by a government official and then recorded as such (and that aint cheap) of course you can cheat, get away with it and take a chance on the boiler maybe bursting full of scalding water)

you get a leak in one of these non pressure models...stick some jb weld on it and go till spring when you have time to fix it right

one thing with the pressurized boiler...likley you don't get a lemon like you might with outdoor ones