Holding tank longevity?

[Frank B]

I have run a heating duct from the furnace across the bottom of the fresh water tank (see http://www.rvforum.net/SMF_forum/index.php?topic=2357.0  for details), and now I'm ready to insulate to be sure that things don't freeze when we winter camp.  On our last old trailer, I had the bottom of it spray foam insulated, which worked well.  However, if anyone ever has to remove the tanks from that trailer, they better burn it instead.    So before I have the holding tanks and fresh water tank spray foamed on our newer unit, I think I better ask some questions.

What is the longevity of holding / fresh water tanks like?  Has anyone had to have them serviced / replaced during the normal life of a trailer?  I can't conceive of anything happening to them other than a puncture.  However, if I have them spray foam insulated, any work on them after the fact is going to be pretty tough.  I'm not concerned about the sensor contacts in the tanks.  They stop working eventually anyway, and they are not a major item in my mind.  I'm more concerned about any common problems that would require removing and installing new tanks.

Thanks for any insight anyone is able to offer.

Frank.

 

[Woody]

I've never heard of anyone tanks actually starting to leak. If they did they would be relatively easy to fix with a fiberglas patch kit. If sensors go bad new aftermarket ones could be installed.
I heard of one guy that left his grey water tank full all winter, it froze and cracked but he was able to get it fixed. The way most are installed it would be almost impossible to remove them unless you dropped them out through the bottom of the coach or trailer.

Woody

 

[Steve CDN]

Holding tanks have been known to burst, due to a variety of reasons.  Also access to the level detectors sometimes need to be accessed for maintenance.

That being said, the use of spray foam insulation itself should be given serious consideration.  This type of insulation is extremely flammable and its use is not usually recommended in an RV.  It's true that some RV manufacturers use it as a way to fill spaces, but when the toxicity from smoke from RV wallpanelling is added to the flammability of spray foam insulation,  in the event of ignition by a 12VDC short circuit the rate of acceleration of the fire could be deadly.

Why not use batts of pink fiberglass insulation, which can be easily removed for maintenance?

 

[Frank B]

Steve:

>when the toxicity from smoke from RV wallpanelling is added to the flammability of spray foam insulation,<

Good point.  I had forgotten about the flammability problem.

>Why not use batts of pink fiberglass insulation, which can be easily removed for maintenance?<

The problem would be affixing them and keeping them dry.  The tanks on this trailer are slung on the underside where they will get mud and snow in the winter.  I'm not able to build a cage for them, as there is just too much work involved.  Spray foam is quick  effective and waterproof.  I don't know quite what to do otherwise.  I might be able to glue some styrofoam panels across the bottom of the fresh water tank, but fumes from burning styrofoam are also terribly noxious.

Frank.

 

[Karl]

Frank,
Not to sound condescending, but if your styrofoam (or anything else) starts to burn, your best bet is to not be inside. Smoke detectors and CO detectors are pretty good these days, and if something way down around your water tank is burning, you're probably looking at a total loss anyway. That's why we have insurance. Better to lose the coach then your life.

For the most part, the heating duct beneath the water tank should do a good job of preventing freeze-up - assuming you use your furnace(s) regularly. That, and having it at least half full. Same holds true for your black/gray water tanks. It takes a lot of cold weather to freeze a large quantity of water, so it's better to keep it topped off if possible; well maybe not the black water tank ;D . The bigger concern (IMHO) would be the small hoses/piping coming from the water tank, up to and thru the water pump and water-fed appliances. Some people keep a 60-100 watt lamp in those compartments; some even use a string of Christmas tree lights run along the piping. You don't have to keep it livingroom warm; just above freezing.  

 

[Frank B]

Karl:

>Not to sound condescending, but if your styrofoam (or anything else) starts to burn, your best bet is to not be inside. <

That is a valid point.  To be honest, if it gets to the point that the urethane around the tanks is burning, it is already too late for the occupants.  However, I am trying to glean some useful information from any who contribute to this thread.  Thread drift is a major problem in most forums, and this one is no exception.  My base question is:  How much trouble does one have with holding tanks over the life of a trailer?  Anything else at this point is outside of the realm of my question, and only contributes to thread drift.

In the thread that I linked to in the original message, I discussed why I cannot use electrical power to keep the tanks from freezing.  I ran the duct under the trailer because of this.  I've already committed to a particular solution for my needs.  My question now has only to do with how to further insulate the holding tanks.

Your comments are well taken with regard to a large volume of water freezing.  It does take a while.  As for the black and grey water tanks, they may need nothing.  It is possible that even the fresh water tank will not need anything besides the heat that I am running under the tank.  I'm also looking at that possibility -- just plain leaving it all bare.  If we park out of the wind, that may be enough already.  As to small hoses, etc., that is probably not an issue on this unit.  The fresh water tank is directly below the pump, which is directly under the furnace.  None of that is likely to freeze.  I could wrap the fresh water feed line between the tank and the pump with fibreglass batting with no problem.  Again, that may be enough.

However, for anyone else that may be posting a response here:  We winter camp in the Rockies in Canada in the Winter. It can be below zero overnight (fahrenheit), and up to about 20 during the day.  Our holding tanks are exposed to freezing temperatures 24/7 while we are away for about 3 to 4 days at a time.  The trailer goes back in a heated garage when we get home, and can be dumped at any time after that, once it all thaws out again.  My main concern is the fresh water tank.  Black and grey water tanks can have a couple of gallons of windshield washer antifreeze added to them to prevent total freeze-up.

Again, for any others that may be responding:  All I need at this point is an assessment of the liklihood that I will have to remove the holding tanks from this unit during its useful life.

Thanks, all, for your willing help and contributed experience.  There is a lot of good experience here among the memebers of this group that I hope to benefit from.

Frank.

 

[Frank B]

Steve:

I decided to check out your advice on the flammability of urethane, and tried this:  I took a piece off the bottom of the trailer and lit it with a match.  It burned for a while, but did not generate enough heat to keep itself alight, and went out after a few seconds.

As Karl has pointed out, if the tanks below the floor are burning, then the upper portion of the trailer is probably already gone by now.    Thought I'd add that for you seeing as how you were kind enough to bring it to my attention.  I do appreciate your input.  However, it looks like the risk is relatively low in this application.  The wooden walls will burn better than the urethane.

Thanks again.

Frank.

 

[Karl]

Frank,

I can appreciate your comments about thread drift, but my response was not specifically aimed at you, but also to others who may read this thread in hopes that they may glean some useful information about related issues.

To answer your question directly, there is no stated useful life for tanks, and the probability of needing to remove them is remote, barring some unusual circumstances like a hard freeze-up, other physical damage, or a manufacturing defect. Keeping your rig parked out of the wind will have minimal effect because, as I'm sure you know, windchill only affects living tissue or damp surfaces by hastening the rate of evaporation and subsequent cooling. If you can  somehow shield the tanks and thereby retain any heat already present, that of course will help.

An alternative to Steve's suggstion of using fiberglass bats would be using the metallic foil 'bubble wrap' which many people use in window and vent areas. I don't know how the R-value compares to foam or fiberglass, but it may be worth checking into.

Stay warm!    

 

[Karl]

Frank,

Just as I was posting my reply, you posted one to Steve.

Your point is well taken - as far as it goes. While urethane doesn't burn as well as wood, it has some other serious attributes. Urethane foam contains urea formaldehyde which, when subjected to high heat, emits toxic formaldehyde fumes. 

 

[Carl L]

What is the longevity of holding / fresh water tanks like?  Has anyone had to have them serviced / replaced during the normal life of a trailer?

Ten years with no repairs or leaks in my 1996 Fleetwood Prowler TT.

 

[Frank B]

Wow, the answers are coming in faster than I can answer them!  Thanks, all.

Karl:

>I can appreciate your comments about thread drift, but my response was not specifically aimed at you, but also to others who may read this thread in hopes that they may glean some useful information about related issues.<

Actually, I thought your comments were right on target. 

Your second-to-last post was exaclty what I was looking for, however.  I hope that I did't sound too imperious when explaining what it was that I needed to know.  When there is no 'body language' to go with it, the printed word can come out appearing harsh, even though that was never in my mind or heart.

>While urethane doesn't burn as well as wood, it has some other serious attributes. Urethane foam contains urea formaldehyde which, when subjected to high heat, emits toxic formaldehyde fumes<

Agreed.  And burning styrofoam generates all kind of bad stuff as well.  And, if I understand your comment about the metallic bubble wrap, that is actually a mylar plastic embedded with fine aluminum to make it reflective.  Mylar is also flammable. 

So, I guess I'll have to weigh the relative risks of using flammable / toxic insulation against the liklihood of a fire that would set the exterior tanks ablaze.

Carl:

Thanks for your supporting comments as well.  I too could not conceive of a way that tanks would be a problem, but thought that I had better ask here first.  As I stated at the outset, there is a lot of valuable experience here that I hope to benefit from.

Thanks again, all!

Frank.

 

[Gary RV_Wizard]

If the tank is well supported it should last indefinitely. Failures come from stress/fatigue at the points it is strapped to the frame - or from freezing. They don't wear out.  Check for hairline cracks around the attachment points. Maybe add some supports before spraying the foam.

 

[Frank B]

Gary:

Thanks for the confirmation.  There is a fairly substantial cradle for the fresh water tank.  Both holding tanks have flanged 'shoulders' that run right across them, and these full-length shoulders are supported on full-length angle-iron beams.

I appreciate all lthe fine comments from people willing to help me out.

Frank.

 

[Karl]

Frank,

No offense taken.

Another thought: I really like Steve's idea about the fiberglass bats but also understand your concern about snow, mud, etc. and affixing them. A spray adhesive or a few lengths of duct tape could be used to hold them in position initially; then a heavy-duty reinforced tarp could be used to provide the necessary protection. You wouldn't want to completely seal the tarp edges as the bats need to breathe.

 

[Gary RV_Wizard]

You wouldn't want to completely seal the tarp edges as the bats need to breathe.

To my way of thinking that is totally impractical for insulation to be installed on the underside of an RV. Even the slightest opening is going to fll with with water and mud and fiberglass bats quickly turn into a heavy, sodden mess when they get wet. Darned near impossible to dry out too.  The only way he could use batts underneath would be to add a water proof belly pan, which strikes me as expensive and perhaps difficult since it wasn't designed for it in the first place.

The spray-on urethane foam doesn't have this drawback. The only problem is that it has to be cut away (not difficult) if the tanks have to be serviced.  Not a technical problem, but it means re-spraying the foam afterwards ($).

 

[Frank B]

Gary:

The guy is coming this afternoon to do the urethane.  Anything is going to have pros and cons.  Urethane has some drawbacks should the unit go up in flames.  However, the tanks would likely be the last part to go, and it is very unlikely, in my opinion, that a fire would start there.

"You pays your money, and you takes your chances" as the saying goes.

Thanks all, for your input and help.

Frank.