Mixing Pressurized and non-pressurized systems.

[rschoensta]

We recently had a wood boiler installed in a very large garage which has two
existing oil fired boilers.

We have not used it yet.

The wood boiler is a non-pressurized boiler.

It has been hooked up directly to the existing oil boilers - no heat exchanger.
These will provide back up in really cold weather or when the wood boiler is not working.

I don't recall seeing this as a suggested option.
The only thing I've figured out that this is essentially converting the whole system to a non pressurized system.

Any problems with this?

 

[stee6043]

Yeah....there surely could be problems with this setup. What kind of piping do you have? Is the water treated? I'd bet your existing oil setup was not intended to be used as an open system and as such you may introduce some corrosion problems, amoung other things, by running it open. Not to mention system pressure. Is the oil system meant to run at open pressures or something higher?

 

[rschoensta]

Well it's a central boiler.
I've done a little more research on this.
Central Boiler on their faq page does say you can hook up their boilers (which are unpressurized) directly to a pressurized system.
Essentially your whole system is now depressurized.
Corrosion then becomes an issue for the whole system.
Anti corrosion chemicals will be used.
I think there is a small test kit which test the water and indicates when chemicals need to be added.

I am wondering if there are any other issues aside from corrosion.

The current system is definitely pressurized.
Two oil boilers with radiant heat for the most part.

 

[in hot water]

you might check with the manufacturer of the oil boilers, they may not approve of that tie in to an open system, regardless of what Central suggests. Many of the cast iron boiler manufacturers now void warranty if their equipment is connected to non barrier radiant tubing due to O2 ingress issues, regardless of chemical treatment. I would think open systems would be the same issue.

Even if warranty is not a concern for you, the cost of a HX and and installation sounds like cheaper insurance. Probably cheaper than an ongoing chemical regiment.

hr

 

[Gooserider]

The other potential issue that might come up is if your pumps were sized to require a pressurized feed in order to prevent cavitation - If so you might find that running open will cause you to start eating pumps (which aren't very nutritious) and getting a lot of operating noise from them.

Gooserider

 

[Paso]

I have a unpresurized 300,000 btu wood boiler and a 140,000 btu oil fired boiler that was designed to be used pressurized and have not ran into any issues the oil fired boiler dumps into the storage tank and the wood boiler returns into the storage tank. I've listen carefully and I can't hear and rusting but who knows