Winter OWB shutdown - will she freeze?

[doctorb]

Due to an airflow problem in my 6 year old e-2300 (see other thread), I shut down from burning this past weekend.  Several threads have been started in years' past regarding the prevention of freezing of the OWB/pipes during the winter.  I have taken the opportunity during this shutdown to check how close to freezing my stove gets.

My system has a 300' run from the shed to my basement of 1 1/4" CB pex pipe, buried 3-4 feet deep.  Once into the basement, I have a loop which allows the water to be immediately routed back to the OWB without passing through the heat exchanger.  In the past, I have left the connection to the exchanger open, so that some of the heat from the oil furnace in my basement can be transferred back to the OWB, preventing freezing.  Not this time.  Now I just have the circulating pump at the stove running, and the water comes from the stove into my basement, going through about 10' of exposed pipe, which then sends it right back to the stove.  So no heat is getting into the water, other than that in the ground and the air temp of my basement.

The stove temp fell over the first 2 days to a level of about 70 degrees.  For the last 2 days, no drop in the water temp has been discernible.  I have double checked by going out to the OB and turning on the computer.  The readouts showed the same thing, taking into account some minor loss of heat during the transport to and from the house.  Obviously, I am not running the fans in the firebox.

Theoretically, the most likely place for the pipes to freeze is where they have exited the ground to enter the OWB.  This is where the insulation is most meager and they are most exposed.  Yet, by continuously circulating the water on that long run underground, the water temp seems to be settled at a very safe level. 

The temps here the last two days are about the same:  high - 32. low - 16.  For us, that's below the average temps for this time of year.  For now, I'm going to continue the experiment.  I am just going to run the pump continuously and see how long it takes for the water temp to drift below 50 degrees.  It would be great if I could leave the homestead for a week or more without having to worry about the OWB or pipes freezing.

[Dave Shepard]

We have two gravity fed spring lines that run continuously. They have not frozen in the last 114 years that my family has lived on this farm. They are not buried very deep, either. I think it would be hard to freeze fast moving water in those lines.

[beenthere]

more without having to worry about the OWB or pipes freezing.

Only have to worry about the pump, that it stays running. ;)

Good thing to be checking out, so you won't have to worry. Maybe an alarm system to monitor the water temp as it circulates and lets you know via phone connection that there is a problem to address.

I have a system to let neighbors know if the house is not heating when I'm gone. I leave one of the three zone pump thermostats set at 50°F, and a light in the window connected to that pump. If that pump kicks on calling for heat, then the light comes on in the window indicating that the other two zones are not keeping up with the demand. Somewhat fail-safe, if the neighbors will watch the window for the light.

[doctorb]

We're in for a cold stretch, if you believe the 10 day forecast.  I'll be home during that period to monitor it.  For my geographic location, there are probably only 2-3 months out of the year where I would have to worry about freezing.  I have an automatic back up generator to handle the power issue.  But you're right, if the pump fails, then it may freeze.

[Holmes]

 You may be getting some warmth from the residual heat buried in the ground.   I believe you will be fine unless the pump quits.

[Farmerjw]

Since the pump is still functioning, why not add antifreeze and get it mixed through the circulation then you could just shut down the pump/whole operation.

[r.man]

I have wondered if you could load an OWB and then shut off the combustion air to keep the system from freezing over a long time. Probably wouldn't be viable with a gasser but with the older style and not taking heat out at the other end it would probably work. A friend of mine burns odds and ends in freezing weather while heating with his air to air heat pump. Has his combustion blower shut off on his Heatmor and goes days with nothing in it but scraps. I always thought that if he filled it he would get a week to ten days or more.

[stratford 50]

Adding Anti Freeze might be more of a problem depending how his system is configured. If the good Dr. is using a plate heat exchanger and the heat exchanger fails which has happened to me it would allow anti freeze to enter his domestic water supply, that wouldn't be good.

[pabst79]

The only antifreeze that should be used is a glycol NON toxic liquid, its meant for hydronic heating purposes with a max 50/50 mix, works great and no worry about anyone getting sick should it spill or get into your domestic supply. I have used many brands on large commercial applications and house boilers and it gives customers a good piece of mind for about 8-12 bucks a gallon.  ;)

[Dave Shepard]

Adding Anti Freeze might be more of a problem depending how his system is configured. If the good Dr. is using a plate heat exchanger and the heat exchanger fails which has happened to me it would allow anti freeze to enter his domestic water supply, that wouldn't be good.

The hydronic heating system in the house shouldn't be attached to the domestic water supply, other than the makeup valve on the indoor boiler, which would act as a backflow preventer. I put a makeup line on the wood boiler side of my plate exchanger, and used a backflow preventer to protect my domestic water supply, even though the boiler is very low pressure compared to the domestic supply.

[doctorb]

A leak or transferrance of water in the large heat exchanger from the OWB to the oil furnace water that runs through my baseboard would not enter my domestic water supply, IMO.  However, if the leak occurred in the portion of the system that heats the DHW, a smaller, separate heat exchanger, it would enter the drinking water.

The pros and cons of adding antifreeze to a large volume OWB system has ben debated here before. 

https://forestryforum.com/board/index.php/topic,59035.msg1117526.html#msg1117526

https://forestryforum.com/board/index.php/topic,53587.msg773251.html#msg773251

https://forestryforum.com/board/index.php/topic,69074.msg1036288.html#msg1036288

The cost of the required volume of non-toxic antifreeze to bring such a system to a protection level of -10 degrees is quite large.  I think my e-2300 has a volume of over 450 gallons.  I do not plan to add antifreeze to my OWB system.

We had another cold night here (for us), 17 degrees at 6 AM.  Temp in the OWB this AM - 67 degrees.  So far, just circulating the water is enough to prevent freezing.  The OWB has been shut down since Saturday (5 days) and the water is not in jeopardy of freezing (as long as the pump runs).

[pabst79]

With that kind of volume, I can see why glycol would be cost prohibitive in a res setup. A good circ pump should keep you out of trouble. If the weather ever drops to sub zero you may have to be more careful. I'm hoping for more mild temps, much better on the wood pile.

[r.man]

I have thought about the idea of water transfer through a heat exchanger but with the extreme pressure difference and my experiences with leaking water pipes I have decided that the risk of contaminating the house water is minimal. Instead I am fairly sure a breach in the inner walls of a heat exchanger would result in flooding the OWB. If you suddenly have water pouring out of your OWB it has either been overfilled cold and is now hot or your water to water heat exchanger is perforated.

[beenthere]

DrB
How long do you expect your OWB to be down? i.e. how long will the experiment run?

Aha!  I see the answer in the other thread... waiting to get the back side fixed up.

[Hilltop366]

I'm wondering if it is practical to drain the boiler and lines to prevent freezing if you have to shut down the fire for a while in the winter?

[doctorb]

I HOPE to pick up the kit this weekend.  That depends upon CB and how they shipped it to the dealer.  If he calls, I'm on my way.

If I were going to be shut down for more than a couple of weeks, assuming we are talking January and February, I would consider draining the OWB.  However, from what I'm learning this time, dependent upon the weather, I might go longer than that.  Certainly for this area of the country, December and March can be cold, but not for too long a consecutive stretch.  What I probably would not do is to shut it down, undrained, and then leave home for an extended period of time.  While I could have a neighbor check on the pump, it's what he would do if I have a pump failure that concerns me.  I probably would set up the drainage hoses before I left, as a backup.  Anyway, just stream of thought typing!  Sorry about that.

[jfaulring]

I've pondered a lot of the same questions with my e1450, I'm a little further more north and a bit colder than the Dr., but it's good to see that there's hope that things wouldn't freeze up. I purposely burried my lines below our nominal frost line (about 4 feet down) with the thought that the 150' out and back run would introduce some heat back into the boiler so long as the pump stayed running. I've kinda wondered what draining the boiler down for an extended period would do corrosion wise; the water with rust inhibitor is keeping the oxygen away from the water jacket/fire tubes. I would think that exposing that area to air would almost instantly start to build some surface rust.

[doctorb]

I, too, have that concern.  I would refill as soon as possible, if I did need to drain the system.

A little warmer today, only 30 degrees this morning.  Water Temp readout on the stove says 60 degrees.  Will continue to monitor.

[Farmerjw]

Doctorb, wow, as I don't have any other heat source, freezing the water would be the least of my worries as my wife would be "overheated" about the situation!  Hope you get your parts and get it up and running again soon. 

[doctorb]

i have an indoor wood stove as backup, and prefer it to my oil burning basement furnace, which is the real backup.  so we're pretty toady right now.

Took a walk down to the OWB tonight.  Getting cold here this evening.  17 degrees now.  Water temp in the OWB is 57 degrees.  I'll continue the experiment.  More cold temps forecast over the next few days.

[doctorb]

This morning 15 degrees at 7am.  OWB water temp unchanged at 57 degrees.

[submarinesailor]

This morning 15 degrees at 7am.  OWB water temp unchanged at 57 degrees.

Good morning Doc,

You stated earlier in this tread that, "My system has a 300' run from the shed to my basement of 1 1/4" CB pex pipe, buried 3-4 feet deep".  At 3-4 feet, your should be below the frost line.  So, I believe your system is now at ground temperature and you shouldn't have anything to worry about.   That's unless we have temperature like we did in 1976 when the bay froze over a long ways down.

Bruce

[Mopar70]

circulating the water will keep it from freezing.
If the water temp drops to freezing temp I would be worried about area's on the boiler that could have no circulation like a relief valve.
It will be interesting to hear what the lowest water temp will be, the underground pipe may pick up heat from the ground.
Heat trace inside of the insulation where the piping comes out of the ground would be a good consideration.
If the water temp started to drop pretty low I would leave the pump running and put an electric heater inside the fire box.

[Mopar70]

Actually... Just thought of this.
A good lightbulb inside the fire box would probably be more then enough.

[UN Hooker]

  Hmmm, the CB insulated pipe doesn't loose heat TO the ground (maybe a couple deg. @ 180*) but can absorb heat FROM the ground to keep the boiler from freezing? Really !!