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 !!

[Mopar70]

I stand corrected
typing out loud
" spaced the obvious underground insulation"
you called me and yourself out on that one.

[doctorb]

Temp is down to 55 degrees this AM.  One part of the system is frozen....the small water level valve at the back is attached to a transparent piece of plastic tubing, where you read the water level in the stove.  That is frozen.  It has happened one time before, when I shut down due to my back not letting me feed the stove, but no ill effects occurred.  Hadn't thought of that again until Mopar's post.  Thanks.

I do not think the temps have fully bottomed out.  My understanding from my reading about geothermal is that the ground temp below the freeze line is about 48-50 degrees.  So I think, potentially, that's as low as the temp may go.

With regards to heat loss to, and now the concept of heat gain, from the ground, my observations tell me that there is energy exchanged from the ground to the pipe and, in this case, visa versa.  When it snows, the ground above the pipe gets covered like any other part of my lawn, and it stays that way for days.  During snow melt, when the snowpack gets thin, the first areas to show grass are right over the pipe.  So some heat gets out.  Not too much, but I do have a 6 degree difference from my stove to my basement.  (This figure may also be contributed to by my differing types of thermometers at each end of the run.)  That energy must be going into the ground during normal stove performance.  Now, I have set up a system where the heat may be absorbed by the pipe, keeping the whole system from freezing.  I'll keep monitoring.

[bandmiller2]

Insulation doesn't prevent heat/cold transfer just slows it down, very interesting experiment. Frank C.

[doctorb]

Water temp this morning at 53 degrees.  I picked up the parts from my "new" CB dealer on Friday.  However, the steel at the back of the stove has bubbled a bit, so the plates they provide do not sit flush against the back wall.  The experiment, however, is officially over.  Had a welder out to my place today who was great.  Removed what needed to go and we placed the plates onto the back wall of the firebox as directed by CB.  Started burning at about 4 PM and was at 185 degrees by 7 PM.

So, what's the take home message? 

My OWB was shut down for 9 straight days during a very cold stretch of weather, and the water temperature only got down to 53 degrees.  Certainly, the key has to be continuing the circulation of the water.  But given the maintenance of water temps in the 50-60 degree range for several days without the addition of additional heat from my basement, I think it very unlikely that this system will ever freeze, as long as the pump remains running.

I learned a lot doing this.

[beenthere]

Great to hear you are back up and running..

[stratford 50]

If possible Dr B, a few pictures would be helpful, well done on the experiment.

[doctorb]

Here's the crack at the back of my stove.  The vertical cut was an expansion joint cut in by CB.  The crack runs from the middle of this now warped expansion cut to an air hole, which is now shaped like a peanut.  What the pics don't show is the bubbled out nature of this steel.



 



 


Her's the cut-out to get rid of the cracked and warped steel:



 

And here are the new steel plates attached to the back wall of the firebox.



 

As a bonus, I finally took the time to learn how to post pics.  Thanks, stratford 50.  I needed to get over that tiny hump and you pushed me to do so.  Pretty easy, I must say.

[bobby s]

I think your firebox might be a bit different than mine. Is that 2" round hole for a gas ignition or is coming from one of the solenoids out back? What exactly is are new steel pieces doing?  Guess I'm missing something. Thanks for posting the pictures and keeping us updated. Glad you're back up and running.

[bobby s]

I think your firebox might be a bit different than mine. Is that 2" round hole for a gas ignition or is coming from one of the solenoids out back? What exactly is are new steel pieces doing?  Guess I'm missing something. Thanks for posting the pictures and keeping us updated. Glad you're back up and running.

Ooops- just realized the steel plates are mounted flat against the back wall. I thought they were held off when I first saw the picture. I assume to force airflow out to side holes.

[doctorb]

Apparently, the area around these back holes generates significant amount of heat, and the steel in this area has been cracking and warping.  CB made these plates for two reasons:  1) As a repair for problems like mine and 2) to enable removal of the plate for better clean out of the air chambers.  My welder told me that they will provide some protection for the remaining steel of the back of the stove, but they themselves might get cracked and warp.  Replacing them will be easy, if that eventuality cones to pass.

Yes, that large central tube is the propane ignition area, which I have never used.  Wish I had not purchased a dual fuel model, though.  That has been a waste of $.  This unit has run well for me and does not let the fire burn out.  Only times I've needed a restart is after a thorough cleaning, like yesterday, or if I was was extremely delayed in returning home.  Very, very rare.  I did not need the gas starter option.

[Mopar70]

ive enjoyed the topic Doc, glad to see your up and running again.
I noticed you did some research on geothermal laws.
Another topic you may find worth researching "the laws of thermodynamics"
I cant help but think and type out loud again...
Snow has an Insulation value.
frost is much more apt to be present in the ground above your piping when there is no snow.
after snowfall, that same frost is insulated from outdoor ambient and is more common to your underground heat source.
depending on the amount of snow, outdoor ambient.. other factors... any existing frost could melt all together.
I never thought about the grass concept but it makes sense to me, warmer ground makes it easyer for grass to germinate.
Think of the possibilities!
you could have all your nieghbors in awe over the size of your tomato plants!!

[doctorb]

Just to let you know that I practice what I've learned through this test, I went away from last Wednesday through today.  During that time, we had no days with high temps >32 degrees and had the coldest temps ever seen by me in all my years in Maryland.  I had never seen a minus temp here before.  We had two days of minus temps for am lows while we were away.

I shut the stove down Tuesday, and just left the pump circulating the water to my basement and back.  No connection to the heat exchanger, so no heat was added from my oil furnace, which kept the house warm while we were gone.  So, this evening, I went to the stove.  Water temperature 62 degrees.  Restarted tonight.

So, even under the coldest conditions, this stove got no where near freezing.  Remarkable.

[Logging logginglogging]

Wow, great pictures, I can easily make some plates like that. my back wall is nice and flat still but I would like to put in a cleanout. I have never seen the dual fuel model of my stove before, where does that large tube go?  doesn't in get junk and gunk in it?

I think I will make a cutout clean out for my stove this year, though Mine has never plugged up before.

[doctorb]

I think that large tube you see in the center is the ignition tube for the duel fuel models.  I have never hooked up gas to my 2300 and wish I had not spent the extra$.  Yes, it get filled with ash and doesn't seem to affect anything.

[JJ]

Hi doctorb,

Thanks for the posting.  I have just returned from 3 week trip where my stove (e-2300 like yours) was shut down.
I have been letting the inside oil boiler keep heat in OWB by heat exchanger and water temp in wood boiler stays about 150F.

It was a lot colder here than where you are (3 weeks 0-10F), but I may try shutting off the inside pump to heat exchanger, leaving only the outside running next time; saving on oil by not heating the stove.

I will like to see if oil use is significantly less by not keeping the stove warm.  I don't think there is too much heat lost by keeping it warm, kinda like outdoor a hot tub.

I see you still have the fire bricks in the side walls, which I had removed years ago.
Oddly my stove (wood only) has not cooked the back plate like yours, but has cracked the left channel air, where I think all my air now gets into the stove.  I tend to pile the wood on the left side (being right handed I guess), as I find out early on, not to pile wood all way across, so it can fall down without bridging as it burns; so maybe I have caused it to crack from hitting it with logs while loading hot.  My logs are too long (20") to load cross-wise.

Reading about your air flow problem puzzles me, as I think with door closed, wood chamber pressurizes, and the combustion happens at the bottom, there the air exits into the reaction chamber.  At least is what I observe with my stove.  I am under the impression, that the cracks do not matter, as long as the door seal is tight.

      JJ

[doctorb]

My unscientific impression, from "protecting" my OWB in past winters through the same method you did, is that the oil consumption is significant.  The water returning to your indoor oil burner has been cooled down close to the temperature of the OWB water.  Do you recall when you returned what the water temp in the OWB was?  Mine, from memory of last winter, was around 100-110 degrees.  Don't hold me to that!

So the water in the OWB acts like a heat sink, pulling energy away from your oil burner.  In three weeks I would bet that you used significantly more oil than you would have thought.  Give us a follow up when you can estimate how much oil you used.  Thanks.

[JJ]

Hi doctorb,
I agree there must be some loss keeping the OWB warm with oil boiler, but how much.
The way I think of it is instead of heat sink, it is heat store.  Instead of oil boiler starting with room temp water (~65-68F), it has 150F pre-heated water from heat exchange.
What I find is boiler fires in short bursts with pre-heated water, instead of long burn.
Anyway, I like the idea of not heating the idle OWB.  In fact the thermostat valve CB sent to me few years ago (haven't installed), seems to imply that CB is fine with unheated OWB in winter, as long as outside circulation pump is running.

       JJ

[beenthere]

If I was going to use the oil boiler to heat water in the OWB, I'd only try to maintain the temp just above the freezing point. Keep the pump running, but kick warm water out to the OWB only if there was a chance of it freezing. Minimum oil burned to ward off a busted pipe, IMO. Anything above that min. temp is just heating the outdoors.

[gspren]

   When I shut mine down I really need to keep it hot due to an out building with toilet and sink getting heat directly from the OWB. This winter I shut down several times for 6-7 days each and while I'm sure I used more oil it didn't seem excessive.