4300 Gallon Plywood Build (3600+ Take 2)

Standard hot water heater, even a small one, is more expensive than a tankless hwh. I'd also have to have a gas connection added to the fish room which isn't a big deal since the gas supply already runs through the ceiling in that room. I would never use a standard electric hwh. Electricity here is far more expensive than natural gas. My house hwh is natural gas.

Water is very cheap here; less than $1 per 1000 gallons use. The fish room is going to be very well insulated, the tank design (5.5" thick walls in most of it), and our mild winters make maintaining temp very easy.

Water bed heaters are extremely expensive to run. They are very inefficient too. I used to have a king size water bed. Took forever to heat it.

I think for the first version I'll do this:

100' pex on pvc frame as shown in last pic I posted connected to solenoid valve controlled by digital thermostat. Water supplied by existing hot water. (Just need to put a splitter on washing machine hot water supply) Open loop exiting into washing machine drain. The pvc frame will have holes drilled in it and be connected to a submersible pump. The holes will face the bottom of the tank so the heated water is forced down as heat rises naturally. The pump will be controlled by the thermostat as well.
 
Another idea, two solenoids and two thermostats.

One thermostat is for the tank and opens the first solenoid to fill the pex.

Second thermostat checks the temp of the water exiting the pex and once it gets hot enough it closes.

This keeps the hot water in the pex longer and only allows it to flow out once it cools.
 
Standard hot water heater, even a small one, is more expensive than a tankless hwh.
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When used for there intended purpose yes, but you also have to figure in cost of the units. The thing that makes your application differ is your not using your tankless hot water heater to heat the tank water directly, you were using it to in effect heat an element that in turn heats the water. In effect you are turning a tankless hot water heater into a tank hot water heater with your 3600 gallon aquarium the tank, albeit at a much lower temp........ be interesting to see how it worked, and it's just my opinion.
 
100' pex on pvc frame as shown in last pic I posted connected to solenoid valve controlled by digital thermostat. Water supplied by existing hot water. (Just need to put a splitter on washing machine hot water supply) Open loop exiting into washing machine drain. The pvc frame will have holes drilled in it and be connected to a submersible pump. The holes will face the bottom of the tank so the heated water is forced down as heat rises naturally. The pump will be controlled by the thermostat as well.
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Just to clarify is the tap water heated and pumped into the pex and aquarium water pumped into the pvc to aid in circultion.....having a little trouble following......
 
Water in pex is supplied from house hot water heater and exits to drain outside tank.

Water through pvc supplied from submersible pump in tank to distribute heated tank water outside the pex.
 
nc0gnet0 said:
When used for there intended purpose yes, but you also have to figure in cost of the units. The thing that makes your application differ is your not using your tankless hot water heater to heat the tank water directly, you were using it to in effect heat an element that in turn heats the water. In effect you are turning a tankless hot water heater into a tank hot water heater with your 3600 gallon aquarium the tank, albeit at a much lower temp........ be interesting to see how it worked, and it's just my opinion.
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No, the water in the pex, however many gallons that is becomes the tank, not the aquarium (which is 4300 gallons now not 3600). The system would work just like they do subfloor heating. It's radiant heat supplied by heating the water in the pex.

The pex essentially becomes the heating element regardless of which way I do this.
 
One of the reasons this works so well is that the radiant temp of the pex is so much hotter than the temp range the tank is maintained at. The cycles of heating and cooling of the water inside the pex becomes smaller and smaller as the tank is at temp and the ambient temp of the room is stabilized. It should take a whole lot less to heat my house in winter with this 80 degree radiator.
 
It should take a whole lot less to heat my house in winter with this 80 degree radiator.
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I was going to say the room the tank is in should be nice and toasty ;)

No, the water in the pex, however many gallons that is becomes the tank, not the aquarium (which is 4300 gallons now not 3600). The system would work just like they do subfloor heating. It's radiant heat supplied by heating the water in the pex.
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I guess it's just a question of semantics on how you view it. You see the pex as an element/tank, whereas I see it as the element in a tank. For instance, an electric hot water heater is a tank in which exists an electric element that heats the water to temp. You have eliminated this electric element and used an element heated by a tankless hot water heater. In my minds eye, now the whole system has become one big electric hot water heater (maintained at 80+ degrees), with the pex the element and your aquarium the tank (assuming the on demand hot water heater is electric).

I guess if this system was economically viable we would (or will) see them to heat swimming pools, etc.

When you figure a comparison between this system and a passive electric heating grid, your going to need to also include the cost to run the pumps, the cost of the water (although cheap it does have cost) and materials. It would indeed be an interesting comparison.........

At any rate, enough said on this, I don't want to be a further distraction and eagerly await the finished product.
 
I'm really liking the 2 solenoid 2 thermostat idea. It addresses the efficiency issues very well.

If it doesn't heat sufficiently/efficiently using the house HWH, I would only have to add a THWH inline. If the pex/pvc frame doesn't work well, I can always use the pex inside a barrel and do it that way.

The little jog over in the tank has a nice place to secure the pvc framing. 4 90s and 3 pieces of pvc and I have a loop outside the tank to secure to the top there.

nc - you're not a distraction. Your ideas are a big help. Initially, there will only be the two thermostats, two solenoid valves, and quiet one 4000 pump to circulate the heated water.

Debating on whether to have the pump on all the time for double duty as circulation or only on when the pex is hot.
 
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