Heat exchanger or direct

[rjohnson056]

Hello,

I am new to this forum and to wood boilers in general. I plan on installing a wood boiler in my garage which is about 75 feet from my house. I already ran the Thermopex. My question is whether or not I should directly plumb the wood boiler supply and return into the existing loops (3 heating loops, 1 indirect fired DHW) or if I should use a heat exchanger before the zones return into the oil burner?

I am concerned with freezing the wood boiler lines in the ground when I go away (I work on a ship and am away for a month at a time) so I am leaning towards using a heat exchanger and gylcoling the loop. This way I would not have to worry about running a circulator 24/7.

My house is approximately 3000 sqf, old and drafty.

Any thoughts/ideas are greatly appreciated.

Thanks in advance,

Ryan

 

[Garth B]

I wouldn't use glycol unless there was an absolute need for it. If the boiler is in a heated space and the water is continuously circuiting it wont freeze. Also if the pex is insulated and buried below frost there shouldnt be any danger of freezing even without circulating. If the boiler is in an unheated space I would use glycol, otherwise you would be relying on a circulator to keep it from freezing up (for long periods of time that would be concerning).

If it is to be a pressurized system your existing pex would need to be O2 barrier type or you will need the xchanger regardless.

*edit, just realized you said you didnt want to run the circ 24/7, I would run it 24/7 if its a heated space in the garage otherwise go with the glycol.

 

[rjohnson056]

Thanks for the reply. The garage is not heated at this time. Any suggestions on a heat exchanger?

 

[Garth B]

Cant suggest any because i dont have one and havent looked into getting one. If you post some info on the output of the boiler you are installing someone may suggest one to you or give some advise on selection.

 

[jebatty]

Any suggestions on a heat exchanger?

If that's your decision, then nail your facts down hard. How many btu's do you need to meet your demand for heat and DHW? What is the minimum usable water temperature that you need to be delivered on the heating and DHW side of the exchanger? What is the size of your storage (you should consider this to be mandatory with a wood hydronic system)? What is the size of your plumbing lines between the boiler and the hx? How much water do you need to move to meet your heat demand (gpm x 500 x delta-T) on both sides of the hx? What is your approach temperature target on the hx? What is the pump head on both sides of the hx? What size circulator will you need to provide the requried gpm's? Answers to these questions will help you get started in the decision process on the size of your heat exchanger.

If this sounds a bit daunting, it is. You have three choices: 1) do lots of research to gain the knowledge needed to install your system correctly (not an easy task, it took me three re-dos and many hours of reading to get my system right, as I started 5 years ago where you probably are today); 2) hire someone who knows a lot more than you do, but importantly someone who has installed modern wood gasification boiler systems, and get references, quiz the customers; or 3) shoot from the hip and just do it, while hoping the hip shot doesn't go through your foot as it ricochets through your bank account.