How long do I generally have before OWB insulated pipes freeze up during a power outage?

[mike758]

I’m going into my first winter ever using an outdoor wood boiler (Heatmaster C150) and I live by myself and work full time so one of my biggest concerns is the unit and lines freezing up if there’s a power outage while I’m away from home. I was looking into adding Glycol but it would cost me about $700 to do a 30% mixture. In the winter I’m usually away from home up to 13 hours a day. I have ran insulated PEX but it’s above the frost line and obviously the lines are bare going into the furnace. I know this question is pretty broad, but I was curious if anyone has had issues with pipes bursting or the unit freezing up while away. It doesn’t get terribly cold here, lows are usually mid 30s and it usually doesn’t go below 20F

 

[sloeffle]

I'd pass on the glycol, water has the best properties for exchanging heat. What brand of insulated PEX did you buy ?

Unfortunately I don't have a good answer for you on how to solve your problem if the power goes out while you aren't home other than whole home generator setup. Maybe a UPS set in back of the stove ? You are in a similar climate as I am, on an average winter day I'd think it would take a pretty significant amount of time for the few hundred gallons of water in your stove to cool down from 180F and freeze.

 

[salecker]

it takes a while for the water to freeze,depending on temp.
I was going to install a low temperature circulatory pump in my system.
It would come on when the water dropped to a certain temp,moving water doesn't freeze up as fast

 

[brenndatomu]

No way to know for sure how long its going to take your system to freeze up, but if its of any comfort, pex will often stretch, not break...I know that doesn't help you thaw out your system when the power comes back on, but at least you probably wont have broken pipes to fix too! Just make sure wherever you have to bare the lines that you go back and put some pipe insulation over them when done...seal all the lil gaps as best you can too, try to keep any cold air out.
Another option would be to set up a battery backup for your circ pump...if you can keep the water circulating, it won't freeze for a long time...the only down side is the cost to set up and maintain a proper backup big enough to do the job.
Its possible that depending on the layout of your system, you could get some thermocycling when the power is out too...would take quite a while to freeze up that way!

 

[yooperdave]

I used to have an OWB and had the same concern as you @mike758 . The temps I experienced during an extended power outage (more than a couple of hours) were in the single digits. The OWB was fine during those hours of no power. But, I also made sure that all lines were insulated. Specifically, the ones that tied into the boiler behind the access door. 👍