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  1. Eric Manning
  2. DIY Float Tanks
  3. Wednesday, October 15 2014, 06:00 PM
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Can anyone suggest a good inline heater that withstand the salt water and keep the temp within a few degrees? I have given up on waterbed heaters, to much mess. And any tricks on lining a wood double sided,insulated tank with fiberglass? Thanks....

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alvar Accepted Answer

I'm looking to build my own tank and have researched quite a lot now. So no experience here, but in theory and as far as I can tell this should work pretty good. Not an inline solution though. Any feedback is appreciated.

I'm planning to use electric floor heating cables rather than a mat. You'll have to do some calculating to see how much length and what kind of cable you need i.e. how much wattage. I plan on using 15m of 4mm cable which leads to 145watt for a 240x150x27cm watermass. Our tank will be isolated with 19cm of cellulose ( check out the soundproofing vid!). These cables come with a thermostat. I think I'm going to order them without and go for a PID deveice instead for accuracy reasons. Here are two dutch website, Maybe use google translate;-) You can proberbaly find an alternative in your area;

I choose cables because they are cheaper than a mat. But for conveinice you could choose a mat. Make sure the cables are insulated so there's no EM-field. Also make sure they are grounded (extra EM-field protection) because this could be a lifesaver. Literally. If you're not 100%, let a professional make sure. I'd do that anyway, just to be sure.

The cables are 230v so they plug into the grid, no transformer. Alarm bells went of in my head at first, but considering they use these in bathrooms all the time and they are grounded I feel it's ok. They're not exposed to the water in any way (read on). Also transformers make noise, these don't. Also transformers break, these don't.

I assume an insulated bottom of the tank with wood flooring. On the flooring put an extra (thin) insulating layer like polystyrene. The more dense the better. I plan on using this: Again a dutch site. This is because you want all the heat to transfer more easily into the water rather than the wood... well duh... It's great if the plate is finische with an aluminum foil. If not do so. The foil is to further insulate the heat form the cables and to poor the cement mixture on.

Next tape the cables on the aluminium foil. Leave at least 10cm from the sides. Lay the cables like this: It's no problem to not cover the entire surface. If you're insulation around the tank is good you proberbly won't need that much. I'd go for the outer rings rather than the inner rings if you have a choice. That way the warmwater circulating will 'push' you to the middle of the tank rather than up and away.

Then, poor on 'leveling cement', not sure how to translate, that's a literal translation. Make sure it's usable for floorheating and it has a high end strength. I plan on using a layer of about 15mm. A combination of thin enough to allow for quik heat transfer and thick enough for protection. Also use an insulating border (tape) so the cement isn't in direct contact with the walls. This is good foor heat insulation, but mainly so the floor can 'work' if it needs to.

There are a few reasons to finsh with cement;

  • The heat from the cables transfer easily to the cement and makes for a larger are to transfer heat to the water.

  • You need something to apply the waterproof finish on.

  • The cables need to be protected againt damaging. Not that anyone is walking in the tank with stilleto heels but still, you may drop something and electrocute yourself. Hence the extra checking for proper grounding. Also, assuming you'll live you'd have to fix the cables which is a lot of work.

As for waterproofing I plan to use EPDM. It's what Crash form floatlabs uses. It's the rubber foil they use in fish ponds as well. Make sure you don't get the roofing kind but the pond kind for health reasons.


Good luck, let me know if this was useful.

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