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Old 01-28-2021, 11:30 AM   #1
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Winter Freeze Protection

Throwing this in general as it appears to apply to all...


Most of us know that the furnace itself helps prevent water lines from freezing. Plumbing is usually run along side / same cavity as ductwork, at least on my trailer and previous.


N. Texas got down to 25F as measured by my thermometer. At 7am, when I went to make coffee, just a trickle of water in kitchen (furthest away from utility area) but other fixtures flowed fine. Within a minute, flow went from trickle to normal. Immersion thermometer indicated water at 32F and climbing. I do use a heated hose.


Normally, we use heat strips to maintain 72 inside the coach. On nights like last night, I switch to furnace. This works well until somebody (not me!) turns furnace off.


This got me to thinking during coffee about adding another thermostat / temperature controller to the furnace. I have confirmed this morning that the 3 button Tstat from Dometic (NOT Touch) has no feedback whatsoever regarding if furnace is running or not. If it gets cold enough, it just closes contacts and turns furnace on. Shorting the 2 blue wires to turn furnace on and tstat remains in heatstrip mode happily converting electricity into heat, eventually.


My Thoughts are to either:
1) use a relay output temperature controller from Amazon. They are plagued by various models that run on 12v.
2) use a snapdisk with 35 close and 42 open.


Either would be used to join thermostat wires to furnace (blue) before the wall tstat connections. Temp controller would give adjustability, snapdisk gives simplicity. In either case, I would have an override / disconnect switch in place for those ah-shoot moments.



Either way, the sense element will be located around half way between utility and kitchen cabinet where pipes emerge. Intent is to measure temp of airspace around the pex.


What are your thoughts / solution if you have done this already?


For the record, utility area was about 58F when this happened. It is kept warm by radiant heat from furnace and 30 gallon Rheem residential water heater (OEM, no water heater cut out).
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Old 01-29-2021, 08:18 AM   #2
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How I heat my Wet Bay.
I have a 12vdc heater installed by the factory in my wet bay, labeled System Heat, but 12vdc doesn’t produce a lot of heat, and the wet bay is about 100 cubic feet, 8.5x3x4 ish. So I added a 120vac heater setup to ensure I have heat in the wet bay that can fight off the 10*F Utah winter nights. First, I bring in 120vac via an extension cord plugged into my pedestal, not into the coach. My coach is plugged into 30 amps and it uses a lot of those amps to charge the batteries when the furnaces and System Heat start gobbling 12vdc like it’s free. The 120vac extension cord comes into the wet bay thru the hole my SaniCon hose would go out. I wrap this cord with a towel such that the hole is full of rolled up towel acting as insulation. Into the extension cord in the wet bay, I plug in a 3-way grounded splitter. Into one side of the splitter I plug in a LED night light to act as a telltale of power. The night light is illuminated showing power to the splitter.
Into the top of the splitter, I plug in a Thermo Cube. The Thermo Cube passes power when temperature falls to 35*F, and interrupts power when temperature rises to 45*F. The Thermo Cube has two grounded outlets, and into each, I plug a 3-way splitter. I plug a small fan-forced ceramic portable heater and a second telltale LED night light into one of the splitters, and a small table fan and a plug-in analog clock into the other. The heater’s is set to high fan force and high heat. The table fan is set to medium force. The clock is set to midnight. The table fan is installed in the wet bay on top of the fresh water tank behind the wet bay panel pointed at the back of the panel and at the water pump. The heater is next to the table fan and pointed 90* to the flow of the air from the table fan. The clock is set on the floor and illuminated by the first telltale night light. When the Thermo Cube senses 35*F, the table fan, the second telltale, the heater and the clock all receive power and begin to run at their preset settings, the clock just starts counting time. At 45*F, the fan, second telltale, heater and clock shut off. The clock shows how much time the fan and heater have run. It was 19*F this morning when I woke up. The clock showed 1 hour and 10 minutes of cumulative run time in the previous 24 hours keeping the wet bay above 35*F. Nice.
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Old 01-29-2021, 08:53 AM   #3
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Quote:
Originally Posted by Krbjmpr View Post
...

N. Texas got down to 25F as measured by my thermometer. At 7am, when I went to make coffee, just a trickle of water in kitchen (furthest away from utility area) but other fixtures flowed fine. Within a minute, flow went from trickle to normal. Immersion thermometer indicated water at 32F and climbing. I do use a heated hose.
...
This got me to thinking during coffee about adding another thermostat / temperature controller to the furnace. I have confirmed this morning that the 3 button Tstat from Dometic (NOT Touch) has no feedback whatsoever regarding if furnace is running or not. If it gets cold enough, it just closes contacts and turns furnace on. Shorting the 2 blue wires to turn furnace on and tstat remains in heatstrip mode happily converting electricity into heat, eventually.

My Thoughts are to either:
1) use a relay output temperature controller from Amazon. They are plagued by various models that run on 12v.
2) use a snapdisk with 35 close and 42 open.

Either would be used to join thermostat wires to furnace (blue) before the wall tstat connections. Temp controller would give adjustability, snapdisk gives simplicity. In either case, I would have an override / disconnect switch in place for those ah-shoot moments.

Either way, the sense element will be located around half way between utility and kitchen cabinet where pipes emerge. Intent is to measure temp of airspace around the pex.

What are your thoughts / solution if you have done this already?
...
You seem to have an excellent grasp of the physics and electrical issues. Consider these additional issues.

The temperature sensor must be placed where the ice blockage occurred. It could be just a spot, or it could be in the middle where you plan to put the thermostat.

Under the right conditions, the furnace will run regardless of the temperature in in the cabin. It could get extremely hot in your living area and consume lots of propane.

Fooling with the design of a dangerous appliance like a propane furnace can have unintended consequences even for the best electrical engineers. Extensive skilled safety testing of changes would be required before selling such an appliance.

There are lots of 120 volt thermostatically controlled devices available to consumers that are designed to keep water pipes from freezing. You can buy heat tape at hardware stores, home stores, Walmart, on-line, and other places. Find one that can be fished through the space and will have temp sensing along the pipe.

You can get heat tape in bulk that can be cut to desired length and will sense freezing temperatures over its full length. Search on-line for a source. It would be far more efficient by only applying heat when and where it is needed.

Some people have reported using a small quiet 12 volt computer cooling fan. Blow into the space from the cabin. Provide a return air vent at the other end of the run for air to exit. A 12 volt thermostat at the exhaust end could control the fan.

I wish you good luck and happy trails ahead!
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Old 01-30-2021, 12:25 PM   #4
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Unintended heating
I had considered that. I was planning on incorporating a snapdisk that would open around 55F just for this scenario. In the beginning, however, I will be using an adjustable temp controller for a couple seasons to get a feel for what limit vs target pex temperature actually is. Would hate for pex to freeze when furnace is shutoff when interior temp achieves 50 or whatever. On same note, will also have to ensure that intended heat setting of 72 from heat strips does not prematurely kill furnace.


A very important point that I failed to mention.



Air Circulators
I already have muffin fan installed in kitchen cabinet. It runs all the time, draws 100mA. Intake through filtered fingerguard near floor, exhaust up high under counter overhang. Works well other than clogging with cat hair. Maybe redundant as cats have fetish about closed cabinet doors and reversing the situation.


I wonder if I can just run furnace fan without ignition to circulate air through ducts, heating the airspace that pex is ran through. That would alter design, but we'll within my capabilities. Hmm. Will have to ensure overheat overall furnace shutdown remains intact.



Furnace Design
Not altering design or operation of furnace itself, just where / how temperature is measured and acted upon. I am considering cheapheat conversion however. *THAT* definitely alters design and function. Still well within my capabilities.



12volt heating
This would be my primary choice for energy source as would have bases covered while pulling through cold climates. But, don't have battery bank or physical room for this endeavor. I do prefer 12v controls.


120vac heating
I love thermocubes! I actually have backup heat in utility area using a 500w ceramic heater. Ran AC through a diode, reduces to 200w. Got airflow directed toward things that will freeze first, like pex coming from water inlet and other area nearby. Turn on is standard thermocube setting. Good idea about putting a clock / timer on 2nd outlet. I actually have no idea if it is or has been needed to run because of cold temps. I do have cheapheat on the to-do list.



Heating Utility Area
Already accomplished with waste heat of furnace and rheem water heater. If I can circulate air in this space so it communicates with pex airspace, then I am golden. However, nuisance things like water tanks, water heater, and furnace prevent access to what I would need. See above. I have insulated reachable pex lines already. 90 fittings are a pain but easy to overcome.



Temperature Sense
I deduced that the halfway point between potential sources of heat would be coldest. But, the point is valid. Perhaps putting the sense element in end of glowrod and moving down length of airspace would be best approach. Find the coldest area when is windy outside. If I ever have to access the pex lines directly, then will insulate and run heat tape along length inside insulation.



So far, I have received confirmation that 2511 series snapdiscs are rated for 12vdc At up to 30A for 30,000 cycles. That was in an email, I have not found the corresponding MH21236 UL testing document yet to nail down testing. At this point is just a statement from manufacturer.


Friend mentioned using diesel Air heater to accomplish my goal. Wabasco would be brand to use, but Chinese copies sure are tempting. YouTube videos have tempered that temptation for temporary resolution of cold temp scenarios using high temp air introduction tempering cold airspace temps. Sorry, Dr Seuss raised his head for a moment. I don't think a diesel heater is in my immediate or near future. Last thing I want is another fuel tank in addition to gasoline, 25g acme propane, and 2x 30# propane. I don't have the room underneath.


I am leaning toward temperature controllers as they have adjustable setpoints. But, I think I will use snapdiscs to prevent any ah-shoot situations.
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Old 01-31-2021, 01:36 PM   #5
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Would it be possible to fish some self regulating heat trace. It's safe to not be taped to a pipe and won't overheat. I kind of assuming this area might be heated with 5watts per foot you could run back an forth it safe to touch itself as well.
If you search recent thread "180f water heater" you can find use of an inexpensive Inkbird digital temperature controller. That can give readout and control of some heating device it is 120v.
At one time we had hundreds of Omron version of these in plant to protect/control chemical process compressors ect . Upgrades have gone more to HMI screens. I used those used ones to upgrade many other analog and thermal controllers and heat trace
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Old 02-01-2021, 09:34 AM   #6
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The temp controller that I settled upon is the DZS -50 to 110C, primarily for its small size (depth) and reviews other than those for miswiring.


I think I will install heat tape, but at later time when I access the area for another purpose. Like stated before, will also insulate as well. I did try to fish in a snapdisc bit something is blocking the glorod. I suspect lines are running through a bulkhead of sorts. I am fashioning a clip/sleeve that fits snugly around the pex, should be able to hold temp probe securely and have a threaded socket for glorod to screw into. Clip will stay on pex and will be guided by pex and glorod will just ne needed for pushing. Hopefully that will get me through whatever obstruction that is present. I have 2in holes everywhere else that are unfilled where pex passes through. I would be surprised if the oem deviated for hole(s) I am trying to get through.


Got the UL documemt about snapdiscs from Senasys. 12v operation is spec'd for non-safety applications only. I am trying to figure out how to attach a pdf to this post.
Attached Files
File Type: pdf 2511 Electrical specs.pdf (15.5 KB, 5 views)
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Old 02-03-2021, 11:56 AM   #7
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Do you want the snap disc switch to be redundant control or overheat protection. Does the controller come with temp. probe long enough. Many controllers can chose/program different types of temp probes. RTD is popular because it doesn't need special wire. Element is kind of higher but wire is not.
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Old 02-04-2021, 03:47 PM   #8
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I find that this system is the most efficient and safe to stay warm in the winter.






OK, I'm going back to hibernation now...
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Old 03-02-2021, 01:40 PM   #9
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So, I had everything in place, setup, connected, and working. Just in time for the fiasco in Texas.

Here is what I did.

I wasn't able to get the temp probe pushed far enough through the cavity to where I wanted it. I had already extended wire length by 20 feet using cat3 data cable.

I did see, however, a furnace duct located about half way between utility area and kitchen cabinet for sink. I cut the temp probe free from the cat3, and soldered on cat5 plenum rated cable, solids for 1 side of probe, stripes for other. Shield was connected to frame at utility end. More on that in a bit.

I used a stepped bit for making hole into furnace duct, as far away from furnace as I could. Pushed the probe in the hole, down the duct, until I could see it in the register I wanted. Made another hole in duct at register, pushed probe out a few inches. With furnace not running on a 40F night, controller indicated 38F. Free air temp, on same controller just prior to duct run was 41F. Super Wool and a piece of aluminum flashing was used to seal hole for entry, head gasket rtv was used at register exit.

Low set point was 35F, turn off was 50. Used a 2nd relay to switch the tstat connection, connected relay coil so that controller provided 12v power, and tied coil ground into controller ground.

Turned on 'master enable' and a bit later, furnace fired. And ran. And ran. Then ran some more. I wasn't getting enough heat into area or I was losing it fast. Furnace did shutoff at 50F as measured by probe, but interior temp was 87F.

Then the winter storms hit. Furnace running, temp stayed about 42F per probe, interior stayed 68-70F. Furnace Did Not Shut Off when ambient hit -2F. That particular morning, I went into kitchen, and no water.

Utility bay temp was 20F. This being with furnace running and its radiant heat. This also with the OEM 30Gallon Rheem water heater gently throwing heat out. Grabbed a cheap ceramic heater, turned dial to where it shutoff inside trailer, and placed it in Utility area. Fresh tank is frozen, most of cold water lines are frozen except inlet and toilet (residential tank). Put heater on low, 700Watts. Closed everything back up, and waited.

Utility area kept dropping temp, eventually everything froze up except inlet (heated hose) and hot water close to water heater. Froze up despite 700W heater pushing heat out. Lowest temp recorded, -1F, highest was 12F with heater, furnace, and water heater running. Still have 40ish at ducts.

So what the hell went wrong?

Recreation By Design misinstalled the furnace in my 5er. How? The furnace return vent, located in bottom of worthless cabinet near door was just more than minimum square inch opening. The wall, which cabinet was attached to and air has to flow through, was maybe a third of minimum.

What was happening is when furnace was running, it was creating negative pressure in utility area, and drawing ambient air in from wherever it could, namely where tank pipes went through the 'floor' and around shore and gravity water inlets.

Turned furnace off, left 700W heater and water heater on, and utility area was thawed out. Kitchen had water again, so it didn't freeze in lines by duct, but in utility area.

Changed controller max temp down to 38, minimum set at 34. Narrow window, but it kept lines flowing without overheating rest of trailer.

We found that a couple of space heaters (harbor freight carpet fans with heater attachments) was able to heat the trailer with 2 heat strips also turned on. Once up to 75F, space heaters turned off, heat strips could maintain temp during the day to about 68F, then had to run space heaters again. At this time, furnace was only run for plumbung, and was maybe 5min every hour.

My biggest problem was bad installation of furnace. That has been mediated somewhat. Full mediation will occur when I replace step to bathroom and move vent to under step. Likely will install couple pc fans to heat utility area when just using heat strips.

I also found the controllers DO NOT like any kind of noise on temp probe. Discovered that with cat3 cable, resolved using cat5 with double aluminum shield, plenum rated.

This spring / summers to-do list just got longer with addition of cutting open bottom of trailer, taping heat trace cable to lines, and covering both with insulation. Then find some way of dealing the 20 foot slice. Probably will use self regulating heat trace, but 12v if I can find it cheap enough. Cheapest so far for 12v is $33/*foot* and not regulated. I do plan to leave furnace controller as is, but overtemp for trailer interior will be by including a battery operated Honeywell thermostat instead of snapdisk. Should give some leeway for mounting, offer adjustability, let me see room temp at a glance vs having to turn off Dometic 3 button tstat and press arrow, and tstat is $5 at home depot and walmart right now.
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