Buderus G215 attached to an outdoor wood boiler question

336mlk

The house I purchased has an outdoor wood boiler and it runs into the basement to a Buderus G215 boiler running on oil in which the oil is a backup if the wood boiler temp drops. The supply pipe coming from the wood boiler goes into the back of the Buderus into the left "Extra Supply Tappings" , and the return comes out the drain.

I always thought how these worked was that there was a heat exchanger between the wood boiler and the oil boiler because the wood boiler is not pressurized and the Buderus system is pressurized. How is the non pressurized hot water from the wood boiler bringing up the temperature of Buderus. Is there a heat exchanger inside the Buderus? I attached a picture of the back of the Buderus. The red/burgandy colored pump at the top of the picture is the pipe from the wood boiler that goes into the left hole and the return is at the bottom of the Buderus which is also the drain for the Buderus.

Ironman

Your oil boiler and house hydronic system MUST remain pressurized, therefore, a heat exchanger is necessary. There is no internal heat exchanger in the G215.

Outdoor wood boiler dealers will tell you that you don't need one in order to keep the cost down to get you to buy their OWB. If your house didn't need to be pressurized, then why have we been wasting the time and money to do it that way for over 100 years? You think that OWB dealers know more about hydronics than the folks in the industry?

336mlk

Not sure if you were going on a rant there lol...Yes I get that the oil boiler has to remain pressurized. My question was how is it heating the pressurized water from the non-pressurized wood boiler. Since there is no heat exchanger that I can see. I was looking for a technical explanation.

Ironman

If there's no HX, then the ODWB is connected directly to the oil boiler leaving your system unpressurized and open to a multitude of problems including premature boiler failure.

Forgive me if I'm a little passionate about this but I'm a hydronics contractor who also sells and installs ODWBs and I've seen too many disasters of this scenario from incompetent and unscrupulous ODWB people doing this.

kcopp

Is the heat exchanger outside in the wood boiler?

njtommy

What is the manufacturer and model wood boiler you have?

hot_rod

Also you do not want oxygen getting into you Buderus. If the OWF is an open/ un-pressurized system you really should have a HX or HX tank to separate the two systems.

Here is some reading about the reasons and method for combining those two heat sources. Maybe pass along the link to the people selling and installing those outdoor units.

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10.pdf

336mlk

Thanks for the comments and additional info. I may have to look into this during the off season and put in a proper HX. The boiler is a Buderus G215. Someone from another forum mentioned that because the ODWB is up the hill about 100 feet from my house with a difference of probably at least 20 feet that there is 0 pressure at the Wood boiler but by the time it gets to the oil boiler there is probably 8 psi of pressure? He mentioned the calculation but I don't remember it off the top of my head.

I figure the guy has been doing it for 10 years actually 13 years now... and so my boiler is about to break at which point I guess I'll have to replace it or I can take steps now if all is still good. I mean for the most part it is working well but at least now I know what is going on rather than be ignorant to everything.

336mlk

Actually I found this in the Central Boiler Manual. Not saying it's right based on the feedback you guys have given me just that they mention this type of installation without the HX.

Ironman

336mlk said:

Actually I found this in the Central Boiler Manual. Not saying it's right based on the feedback you guys have given me just that they mention this type of installation without the HX.

My point exactly in my earlier post: they are NOT hydronic people and they don't seem to realize all the issues involved. The very page you posted, with which I'm all too familiar, contradicts itself. It shows the ODWB on the same plane connected directly to the house boiler. It states that the ODWB must not be pressurized but the indoor boiler system must be purged of all air but not be pressurized above the setting of its relief valve which is normally 30 psi. Please explain how that the ODWB is not gonna be pressurized in that scenario but the indoor boiler will be?

Please take the time to read the Caleffi iDronics 10 issue in the link the hot rod provided. It's very informative and comes from the most respected engineer in this industry - John Seigenthaler.