Retrofitting heated tanks

[Frank B]

We just bought a 2000 lightweight 23 foot 5th.  We Winter camp.  This 5th has forced air ducted heating, but all of it is above floor level using 4" flex hose.  I am interested in adapting this to keep the below floor level tanks from freezing in the Winter.

What is ordinarily done on trailers manufactured with heated tanks?  Are there complete enclosures around the tanks that are fed with furnace air, or are the ducts simply run in close proximity to those tanks?

I am thinking that if I re-direct some of the ducts below floor level to the opposite side of the trailer that I can run ordinary 4" metal ducting close to the tanks.  I will then have the bottom of the whole trailer spray-foam insulated -- tanks, ducts and all (but not between the ducts and the tanks so that some conduction will take place).

The other issue I face is keeping the batteries warm enough so that they don't freeze when discharged.  Do today's 'no maintenance' batteries give off enough gas that heating the area under the dining area seat and then blowing it back into the trailer will be a problem?  I plan on installing the batteries there.  It can be done by simply blowing hot air into that cavity and then letting it out through another hole into the trailer (allowing battery gas, if any, into the trailer) or by running a 4" metal duct close to the batteries and then back into the trailer.

Suggestions appreciated.

Thanks

Frank.

 

[John From Detroit]

One of the things I'd like to see in an anaylis of how much heat it would take to keep the tanks from freezing on an RV

In days of old when my daughter was bold and played in Livonia Youth Philharmonic of Michigan I was "The Bagal Dad"
What this means is, I kept the coffee service (The rules were you either kept the coffee service or bought bagles, Due to the type of vehicle I had and the type of trailer I had (Plunty of room in both) I offered to keep the coffee service for like 3 years, that way I did not have to buy bagles)

I stored it in a 13 foot Scamp trailer during the week.. In the trailer was a freeze switch (35 degree thermostat) and a 100 watt light bulb,,, All but the coldest days, no freeze when I picked up the hardware at 0800hrs on Saturday morning  On the coldest days I had a slightly larger heater (1kw)

 

[Jim Dick]

Frank,

The heated tanks I have seen on trailers are usually special electric blankets glued to the tank. Normally there is no enclosure around the tank. I'm sure if you had an enclosure you could duct the hot air to it and insulate around it. That's pretty much the way motor homes are done. The tanks are inside the bay and heated with hot air.

John has a good point about the 100 watt light bulb. If the area is enclosed it produces quite a bit of heat. I used to keep my garden tractor warmed by putting the bulb under a tarp. Started up in freezing temps with no problem.

 

[Frank B]

John and Jim:

>I'm sure if you had an enclosure you could duct the hot air to it and insulate around it. That's pretty much the way motor homes are done. The tanks are inside the bay and heated with hot air.<

I don't have an enclosure, and don't particularly want to build one unless I really have to.  I was trying to find out what the commercial builders consider necessary, though, before I make a decision and then find out that I either have too much or too little heat to do the job.

>The heated tanks I have seen on trailers are usually special electric blankets glued to the tank.<
>In the trailer was a freeze switch (35 degree thermostat) and a 100 watt light bulb,,, All but the coldest days, no freeze when I picked up the hardware at 0800hrs on Saturday morning  On the coldest days I had a slightly larger heater (1kw)<

Sorry I didn't make this clear in the original post, but we boondock in the Winter.  No shore power.  Electrical heating is therefore out of the running.  That is why I was looking at redirecting some of the ducts.  Propane we have in abundance.  Electrical power is the one that we have too little of.

To some extent, just insulating the tanks will keep things in good shape.  Some of  the heat from the floor will naturally seep into the tanks and keep them from freezing.  However, as we camp in the mountains in Canada in the Winter, it can get reasonably cold at night.  I need some 'insurance' against freezing, and that is why I was looking at putting some heating ducts close to the tanks before I insulate the whole works into place.  Once that spray-foam insulation is in place, it is difficult to remove it to make any changes.  One has to 'grind' it out with a wire brush, and that is messy at best.

Any thoughts from anyone now on the battery enclosure heating?

Thanks.

Frank.

 

[Jim Dick]

Frank,

Since your tanks are not enclosed I think the heat ducts would have a tough time trying to prevent freeze up.

 

[Gary RV_Wizard]

Depending on the temperature extremes and the duration of sub-freezing temps, your tanks may not be a problem anyway. Freeze-ups are more likely to occur first in the fresh water lines and the pump, which are often exposed as well.  Insulating them may be sufficient to prevent overnight freezing and some heat tape wrapped around them may do the job if insulation alone is insufficient.  You can also try insulating the exposed surfaces of your tank, either with automotive insulation (like the underhood stuff) or a spray on foam.

 

[John From Detroit]

Humm... I have never seen an RV with exposed tanks Trailer or Motor home, Mine are in the storage compartments, outside the living space but enclosed non the less (with heat ducts funning over or under them)

There is no real good solution in your case... Any kind of heat other than the furnance would likely cause more problems than it would solve

I can think of ways to heat the underside of an RV when it's not occupied.. but I would not wish to sleep in it (mostly cause you would never wake up) so long as that heater was running.

Insluation and re-ducting are thus your only options.

Or,,,, A small water heater and circulate hot water around them.. This could be done two different ways but the engineering is a bit of a trick... I could design it easily (i suspect many here could) but it would be expensive

 

[Frank B]

Jim:


>Since your tanks are not enclosed I think the heat ducts would have a tough time trying to prevent freeze up.<

What I had in mind was to run a heat duct between them, then spray foam the whole area together, tanks and all (except between duct and the sides of the tanks, of course).  The spray foam would become the enclosure.  That would work for the waste water tanks, but may not be necessary.  I can just put salt or windshield washer antifreeze in them.

Gary:

>Depending on the temperature extremes and the duration of sub-freezing temps, your tanks may not be a problem anyway. Freeze-ups are more likely to occur first in the fresh water lines and the pump, which are often exposed as well.  Insulating them may be sufficient to prevent overnight freezing<

I assume you mean insulating the tanks?  Pump is under the furnace, so should be alright, and water lines are well back from the sides of the unit.  I will be spray-foam insulating the bottom of the trailer and the tanks for sure, as it remains below freezing 24/7 when we Winter camp, and it is just a matter of time before outboard freshwater tanks freeze.  Spray foam insulation is what I had on our smaller 5th, and had no problems with the blackwater tank freezing (there was no grey water tank on that older unit).  In any case, with the waste water, a jug of windshield washer antifreeze might be enough there.

Heating tape is not an option, as we are on battery power when we Winter camp.

John:

>Humm... I have never seen an RV with exposed tanks Trailer or Motor home<

I've never seen a trailer with enclosed ones!    These tanks are slung on racks just below the floor, between the frame rails.

>There is no real good solution in your case... Any kind of heat other than the furnance would likely cause more problems than it would solve<

That is what I am thinking as well.

Well, it looks like I'm on my own with this, as it appears we have no one here at the moment with Winter camping expertise.  Once I get this done, then I guess I'll be the expert in that department.    I thank you all for your suggestions.

At the moment, it looks like I will have to remove the fresh water tank, remove the insulation between it and the floor, and then sling the tank up about 1/2" higher in the cradle so that it touches the underside of the floor.  I can do that by adding spacers to the 'cage' that it sits in.  that will gain me about 1" total between bottom of tank and bottom of cradle.  Bottom of cradle can then be sheeted with some sheet metal or 3-ply, and spray insulated.  One duct can be directed below the floor, into the 1" space at the bottom of the cradle, and back up under the the cupboards on the opposite side of the trailer (which, by the way, is where a lot of the water lines run. 

Another possibility is to mount an additional fresh water tank above the floor under the seat in the dining area.  This is unused space in this unit at the moment, and I could probably get a 30 gal tank in there and not have to heat it at all.

I'll let you know how it works. 

Frank.

 

[Gary RV_Wizard]

If it is below freezing 24/7, then I think you are on the right track, insualting everything.  The only people I know of who winter camp have rigs designed for it and already well insualted (what is commonloy called an "arctic package").  Upper scale trailers and most motorhomes are already fully skinned underneath and often insualted/heated as well.  You will be creating the same sort of thing.

If you are in one place long enough, consider adding some form of skirting around the outside, between the sides and the ground. Even a snowbank.  Preventing cold air circulation underneath the RV will help a lot.  Those who have a permamnent set up ofen use bales of hay around the outside, but that's a bit much if you are only going out for a weekend!

Let us know how it works out. As you say, you can become the expert in this.

 

[Frank B]

OK, things are progressing.

The fresh water tank is slung in a cradle made of angle iron.  Between the bottom of the tank and the bottom of the angle iron 'rungs' there is about a 1" space.  I cut a slot in each end of the cradle, and adapted some 4" furnace ducts to feed those slots.  I then boarded-over with a piece of 3-ply the 1" cavity between tank and bottom of angle iron.  I cut a 4" round hole in the floor of the trailer near the furnace, and have re-directed one of the furnace ducts down through the floor, and through the 1" cavity I created under the fresh water tank.  I am in the process of re-routing the far side of the cavity through another duct back up through another hole in the floor, and into the storage compartment at the back of the trailer, where the fresh water pipes run.  So far, a fair amount of heat flows through this cavity just fine.  Now I may end up with warm tank water!

Once the ducting is in place, the fresh water tank needs to be spray foam insulated to retain the heat, as well as the ducts themselves, both front and rear.

Photos to follow.  How do I attach the photos here, and what size should they be?

Thanks.

Frank.

 

[Frank B]

OK, lets try inserting these images:

First one is how I cut and narrowed the opening on the 4" furnace vent so that it had a 1" opening.  I just slit the narrow sides, folded them over one another, and put one pop rivet in each end to hold it shut.

Second one is the cradle itself showing how the side is made.

Third shot shows the metal I cut out to make a 1" opening.

Fourth shot shows how the furnace duct fits into the opening.

Fifth shot shows an additional picece of angle iron welded over the cutout to replace the metal I removed for the duct.  Just cutting the cradle like that would probably weaken it too much.  This last shot also shows the 3-ply screwed over the angle-iron 'rungs' of the cradle to make the flat duct between the tank and the bottom of the angle iron rungs.

I'll add more pix later showing the cradle back in the trailer with the furnace ducting installed.

Frank.

 

[Frank B]

OK, here are a few more shots:

First one is under the seat in the dining area.  The furnace is located behind the seat just above floor level, and the stock installation wasted a lot of space by just running flex hose to two air outlets under the seat area.  One I re-routed in a more direct line against the outer wall of the trailer, and the other is now connected to the duct that goes through the trailer floor.  The duct is not sealed yet around the opening to the floor, but should be this weekend.  The black circle on the floor is just a piece of rubber mat that I cut from the sealing membrane on the bottom of the trailer.  It is just sitting there, and is not another hole.

Second shot is the underside of the trailer showing where the heating duct comes out, and how it is attached to the cavity I made in the cradle under the fresh water tank.  In this shot, it is just pushed into place.  I will attach supports to the 4" aluminum pipe to make sure it stays up before I spray foam the area.

The third and last shot shows the output end of the cavity with the furnace boot strapped into place on the back of the cradle.  This boot will now be connected to another elbow and go up through the floor into the storage area under the rear bunk.  The fresh water lines to the back of the trailer, toilet, sink, etc. are run through this storage area.  I have a dryer outlet with a screened opening as an outlet, which should prevent items in the storage area from either blocking the outlet, or falling into the duct.  Hope to have all this piping done and secured this weekend.

And, yes, that is my big foot there in the picture.    Though I jacked the trailer up and put it on jack stands, there is still not a lot of room under there for me and my creeper.

Frank.

 

[Gary RV_Wizard]

Thanks for posting the helpful pics, Frank. They are "worth a thousand words..."

 

[Frank B]

Gary:

>Thanks for posting the helpful pics, Frank. They are "worth a thousand words..."<

Though this may not be a common retrofit, seeing as how most of the members here spend their time in warmer places, I do hope that this little project may be of use to someone other than myself.

I'll have perhaps two more shots to post once the install is completed.

We have our first Winter outing booked for the middle of February.  Hope to be able to report back shortly thereafter as to how this works.

Frank.

 

[Frank B]

OK, here is the 'finished product'!

First shot is the hole I cut in the floor for the return air under the lower bunk in the back of the trailer.  I figured out from the underside where the hole had to be, measured above and below to be sure that I would not come up in a bad area above-floor, then drilled a pilot hole from the bottom up.  The pilot hole was right where I had hoped it would be, so I cut out a 4" hole with a jig saw.

Second shot is the return air duct siliconed into place.  I used a good marine grade RTV type silicone, so it set pretty stiff, and will keep the joints in the furnace pipes from separating.  I did the same on the front feed pipes as well, and then strapped them into place with nylon tie-wraps.  The return air pipe is so short that it did not need further mechanical attachment.  In the background you can see the messy job I did of putting urethane spray foam around the furnace boots connecting to the cavity under the fresh water tank.  I forced a fair bit of that product into that area to make sure that all gaps were sealed.

Last shot is the finished cargo area with the screened dryer outlet in place.  I took the 'flapper' valve out of the dryer outlet, and then screwed it to the floor.

There is a fair bit of airflow through that pipe, so I may end up with more heat than I really need back in this area.  However, propane heat is plentiful in this unit, and the more we heat it, the colder it can be outside without having any problems.

The last step now will be to have urethane foam commercially applied to the bottom of the fresh water tank, the bottom of the cavity I made under the tank, around the 4" furnace pipes, and probably around the two holding tanks further aft in the trailer.  I don't care a lot if the holding tanks are not heated, as I can put some sort of antifreeze in them.  However, insulation and natural bacterial action may keep them from needing too much else unless it gets really cold.

As mentioned earlier, we will give it a trial run toward the last half of February.  We're going to try some cross-country skiing in Kananaskis Park in the Rockies then.  I'll report back how things worked out.

Frank.

 

[Frank B]

Well, here is the next report.  All temperatures in Celsius.  Multiply by two and add 32 for Fahrenheit (approx).

I did have the back half of the trailer spray-foam insulated, which covered not only the fresh water tank but also both of the waste water holding tanks, which I did not specifically heat.  Yes, there are trade-offs.  However, I don't see any really practical way to insultate that area short of spray foam.  Urethane spray foam is also quick, easy, and protects and water proofs the whole area for a reasonable price.

We went away this past weekend into Kananaskis Country in the Canadian Rockies at about the 5,000' level.  One would think that this would be a good test, but it seems that perhaps global warming may be a reality after all.  There was not enough snow to cross country ski on, and temperatures did not get below -5 from Feb 2 to 5 when we went.  Highs were around +1 to +5 on Sunday.  Hardly a real test of my winterizing.  Two years ago it got down to -15 at night, with highs around -5 during the day.

We may go again in two weeks into the Crimson Lake area around Nordegg, which is just north of the "Chinook Belt" here in Alberta.  A Chinook is a warm wind that blows over the Rockies from British Columbia when weather conditions are right.  This is common during the Winter from around Lethbridge to Red Deer.

We went further into the park about 31 km. for some skiing.  There the temperature was about 2 degrees lower, and there was a bit more snow.  Cross country skiing at around the freezing point in the middle of the Rockies was a beautiful experience.  Amazing for this time of the year.

As I suspected, the water in the fresh water tank was tepid after a couple of days with the furnace heat running in the trailer.  I ended up with too much heat in the storage area, and now I'm trying to decide what to do about it.  I can either 'T' the feed line under the dining room bench and run half of it back into the trailer living area under the kitchen table, or I can bore a hole between the storage area and the bathroom, and allow some of the heat to trickle into there, coming up under the bathroom sink.  I haven't decided which is going to be best yet, as the bathroom already has its own heat duct, and is quite warm.  In the meantime, the storage area was a great place to store our ski boots!  They were nice and warm when we went to put them on. 

Overall, however, I think the project is a success.  I'm sure we'll be fine for weather as cold as we are personally willing to face.  If we ever get any really cold weather this year, I'll give it a try again.  Our last trailer was good to about -15 before the water lines froze.  On that trailer, however, the lines were run much closer to the outside walls.

So, the conclusion is:

Retrofitting furnace heat to outboard water tanks is feasible.  This allows boondocking in colder climes with no fear of freeze up, and without killing batteries by trying to use electrical heat..  Much will depend on the layout of the trailer, and the way the tanks are attached.  If the fresh water tank is above floor level (as in our last unit) then probably nothing has to be done.  If it is below the floor, as in our present unit, then running a heating duct across the bottom of the fresh water tank, then spray-foaming the area works quite well.

Some tanks are strapped-in, as opposed to being in a cradle like ours, and some tanks have flanges that are supported on rails.  For that, one would have to build a flat duct to run across the bottom of the tank, or along side of it.  However, your local heating shop should be able to fabricate something like that for you.  The rest is just a case of looking at where you can run the ducting.  I was able to do the whole works myself for about $300 CAD, and that included the commercially-applied urethane insulation.  There are urethane insulation kits that you can buy to 'do it yourself.'  However, the cost is high, and I can only imagine it being very messy.  Pay the nice man and get a professional to do the insulation for you.

I used copious amounts of commercial-grade RTV silicone sealant where the pipes went through the floor.  However, these areas were covered with the urethane foam afterward, and probably didn't require that amount of sealing.

Other than that, I am pleased with the results.  Time will tell how effective they will be in colder weather.

Frank.

 

[King]

Just a thought...
If you leave your propane water heater and your water pump on, with just one thermostatically controlled valve, hot water can be returned to the tank.  The return tubing can be routed along water supply lines and around batteries and waste tanks.  Obviously, additional insulation will reduce the amount of propane required.

 

[Frank B]

King:

Yes, that is another way that it could possibly be done.

Anyone want to try it and let us know how it works? 

Frank.

 

[Gary RV_Wizard]

Glad to hear it worked out OK, Frank. Thanks for the report.

 

[fulltimedreamer]

Frank B,

Great job.  It looks like you have solved your problem. As to there not being trailers and fivers with enclosed tanks.  There are several on the market that are good for four season use.  Our Mountaineer has an enclosed belly with heat ducts keeping all the tanks above freezing for winter camping.  We have used ours in the single digits Fahrenheit with no problems.  Of course we do not connect to shore water or sewer at those low temps.  Anyway, congrats on successfully heating your tank.