Dolphina Posted April 12, 2015 Share Posted April 12, 2015 Hi all, I pulled the cardboard and insulation off my Atwood 6gal hot water heater looking for a leak and now need to re-insulate. I am thinking of using "Great stuff" low expansion spray foam for recovering the tank instead of rolled insulation. I was going to lay in cardboard underneath and start by spraying it there then working my way up, and taping cardboard over the outside of the finished job. Any thoughts or comments would be appreciated. Quote Link to comment Share on other sites More sharing options...
zero Posted April 12, 2015 Share Posted April 12, 2015 Hi all, I pulled the cardboard and insulation off my Atwood 6gal hot water heater looking for a leak and now need to re-insulate. I am thinking of using "Great stuff" low expansion spray foam for recovering the tank instead of rolled insulation. I was going to lay in cardboard underneath and start by spraying it there then working my way up, and taping cardboard over the outside of the finished job. Any thoughts or comments would be appreciated. Greart Stuff or any other "closed cell" foam is probably the best thing you can use. Unlike fiberglass - it can't lose it's R-value by getting moist. Just stay away from anything that is "open cell." Quote Link to comment Share on other sites More sharing options...
Dolphina Posted April 13, 2015 Author Share Posted April 13, 2015 FYI all, I contacted Dow Chemical and they advised against using it and restated what is on the can: "...may combust if exposed to flame or tempertures above 280 degrees". Not sure which way I'll go now, but pretty sure the tank doesnt reach 280 degs. Quote Link to comment Share on other sites More sharing options...
snail powered Posted April 13, 2015 Share Posted April 13, 2015 Hi all, I pulled the cardboard and insulation off my Atwood 6gal hot water heater looking for a leak and now need to re-insulate. I am thinking of using "Great stuff" low expansion spray foam for recovering the tank instead of rolled insulation. I was going to lay in cardboard underneath and start by spraying it there then working my way up, and taping cardboard over the outside of the finished job. Any thoughts or comments would be appreciated. The low expansion spray foam does not have terrific R value as it is not dense. It is formulated to be soft and not dense so that it won't warp the casings around windows and doors. It states right on the product information that it is intended for preventing drafts and that really is its sole function rather than being a dense insulation with high R value. It would also be difficult to control the application and cleanup. However with a fiberglass blanket it is super easy to control the application and easy to avoid air gaps against the round tank. There is also easy cleanup and the installation of the fiberglass blanket only takes a few minutes of time. Then instead of cardboard you could create a box out of foam board. On the surface facing towards the tank cover it with aluminum duct tape. That shiny surface of the tape will reflect any escaping heat back towards the tank. Plus the tape will seal any air gaps on the edges of the box. One of the advantages of removable insulation is you can inspect the surface of the tank should you ever wish to do so. But with sprayed on foam you can't do that. Quote Link to comment Share on other sites More sharing options...
Dolphina Posted April 13, 2015 Author Share Posted April 13, 2015 Thanks so much for your input Corbin, you really cleared up the whole process and pointed out some good issues I hadnt considered. Quote Link to comment Share on other sites More sharing options...
zero Posted April 13, 2015 Share Posted April 13, 2015 FYI all, I contacted Dow Chemical and they advised against using it and restated what is on the can: "...may combust if exposed to flame or tempertures above 280 degrees". Not sure which way I'll go now, but pretty sure the tank doesnt reach 280 degs. Just about all cured spray foam based on polyurethane-plastic has an ignition point up around 275-300 degrees F. That worries you? Are you insulating a hot-water heater or a steam boiler?? Granted I'd keep the foam a good distance from the burner. Many RV compaines are using spray-foam to insulate hot-water heaters. What Karin stated about R value is not true with all spray-foams and "density" itself has little to do with it. At least the way the word is being used in advertising literature. The key is the amount of trapped air. "Closed cell" foam typically has an R-value of 6.2 per inch. "Open-cell" foam a value of only 3.7 per inch. NOTE that Great Stuff from Dow is adverstised as "closed cell." Fiberglass when DRY and expanded has an R-value around 3.1 per inch. When it gets damp, much less. I try not to use fiberglass wool on anything anymore unless it is very well ventilated. It gets damp and becomes useless in may applications (in RVs) and also - mice love it. Quote Link to comment Share on other sites More sharing options...
Vanman Posted April 13, 2015 Share Posted April 13, 2015 I always wondered about that. I have to use a mask and gloves to handle it, but the rodents rip it up to make nests of it??? Quote Link to comment Share on other sites More sharing options...
Maineah Posted April 13, 2015 Share Posted April 13, 2015 The tanks originally had Styrofoam half’s that covered the tanks top and bottom. If there is water in the tank it will never go above 212*. It says here in the fine print if you use fiberglass insulation it should be fine and there would no reason for it to get wet unless the tank was leaking. Quote Link to comment Share on other sites More sharing options...
snail powered Posted April 14, 2015 Share Posted April 14, 2015 Remember that whatever you do you want to be able to remove the water heater from the motorhome in case you ever need to replace or service it. That means your new insulation if fixed in place such as a sprayed on foam should not be any larger than the opening you have in the side of the RV that it went into. That opening size is standardized on most RVs according to the size of the tank. If you have rodent issues that most certainly needs to be addressed but I don't think it should necessarily determine your choice of insulation. I found a many years old mouse nest in my RV where they had chewed into the rigid foam insulation to create the nest. The mice did not attack my water heater insulation which was actually the only fiberglass insulation any where in the RV. Meaning they were not specifically attracted to it. It is a good idea to inspect the motorhomes for potential entry points. In my case they were coming up through holes in the floor that were for the vent riser pipes for the two tanks. There was also a similar situation around the gas tank filler tubes where they went down though the floor. They were drilled to a diameter larger than the pipe itself. I used spray foam to seal around the pipes for draft prevention and then cut sheet metal to cover the gaps and screwed it to the top of the floor boards. Even if they clawed through the spray foam they won't be able to get through the metal. I did put grommet along the edges of the metal to prevent it from damaging the tube from any rubbing against the tube movement while on the road. Quote Link to comment Share on other sites More sharing options...
Dolphina Posted April 14, 2015 Author Share Posted April 14, 2015 Update: I felt under the tank and found water so I pulled the whole unit out today. There was scale on the bottom of the tank so, it may be a leak in the tank wall. I also uncovered rotted wood directly below the drain plug and continuing back along the floor next to the outside wall. So now I have another question, (as the first is now moot) Who of you has replaced your floor or parts of it? Again, thanks so much for all the replies, its greatly appreciated! Quote Link to comment Share on other sites More sharing options...
snail powered Posted April 14, 2015 Share Posted April 14, 2015 Update: I felt under the tank and found water so I pulled the whole unit out today. There was scale on the bottom of the tank so, it may be a leak in the tank wall. I also uncovered rotted wood directly below the drain plug and continuing back along the floor next to the outside wall. So now I have another question, (as the first is now moot) Who of you has replaced your floor or parts of it? Again, thanks so much for all the replies, its greatly appreciated! you will find a lot of threads on the forum describing in detail various floor replacement projects. Always good to search the threads as well as ask since people come and people go and the answer you might need could be in the archives. Quote Link to comment Share on other sites More sharing options...
zero Posted April 15, 2015 Share Posted April 15, 2015 Update: I felt under the tank and found water so I pulled the whole unit out today. There was scale on the bottom of the tank so, it may be a leak in the tank wall. I also uncovered rotted wood directly below the drain plug and continuing back along the floor next to the outside wall. So now I have another question, (as the first is now moot) Who of you has replaced your floor or parts of it? Again, thanks so much for all the replies, its greatly appreciated! I've replaced many floors in RVs. Keep in mind, unlike a house - RVs rarely have any spaced-on-center floor joists for strength. RV floors are often multiply and rely on all materials to be in good shape and glued together for offer any overall rigidity. You'll have to figure out what your's is made of and how far you have to go to get out all the rotted wood AND all the wet-wood. You may find out there is MUCH more then you think. Often a visible rot-spot is just the "tip of the iceberg." Also - when replacing plywood - get something with the best wood and most plies. Not something you're likely to find at a Home Depot, Lowes, or local lumber yard. Marine plywood is made from a rot-resistant high-strength wood like Fir is usually the way to go. All depends on what is available to you locally. I just fixed an RV with some 3/8" marine 4-ply Fir that is MUCH stronger then the crappy 3-ply Pine my local yard was selling. If you can get your rot out and reach dry areas - a good constrution glue will enable you to add solid strips of wood for fasteners (to later add plywood to). Finding dry wood is the key. Often wood in an RV weighs twice what it did when installed and is waterlogged. At least it's common here in the Northeast and Midwest. Some RVs use a sandwich of thin plywood glued to a foam center and then a floor-layer of 3/8" plywood. I know Minicruiser and Chinooks used Douglas Fir for their wood. I don't know about Dolphin. Consider yourself luckly and it's not a Chinook. They use a honeycomb-carboard material for a floor and are very hard to repair. Back to your waterheater - that you say is a "moot" subject now. If you live in an area with a lot mice - foam is way to go. They'll chew on it but unlike fiberglass, won't make mulitple nests in it and live in it. Quote Link to comment Share on other sites More sharing options...
Dolphina Posted April 15, 2015 Author Share Posted April 15, 2015 One final note; the factory styrofoam "clamshell" covers are available for $17 - $25 online. You can also get just the tank if your heater is still good. I am installing a new unit (Amazon/Johnson's Surplus). Thanks for all the input. Quote Link to comment Share on other sites More sharing options...
Maineah Posted April 16, 2015 Share Posted April 16, 2015 The difference between a tank and the entire unit is not a lot ($30-50) and you need a tool or good imagination on how to make one to install the retainer on the tank that holds it to the assembly. A new unit comes with the Styrofoam insulation. Quote Link to comment Share on other sites More sharing options...
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