Use hot water to heat the tank during power outage

[ReefBeta]

I just went through a 16h power outage. The circulation problem is solved by battery backup. The tank dropped to 71F by the end. Now I'm consider options to heating for the tank during power outage.

Generator is difficult for me for various reasons, so I'm looking for alternative if available. My house is heated by heat pump, so it will be out as well. My water heater is gas, so hot water still works. During this outage, I fill up hot water in ziplock bags into the tank to warm it a bit. But it's hard to keep doing it while also taking care of the rest of the family.

So I'm thinking, what if I run a long roll of PEX pipe from a faucet, leave good portion of it coil up in the tank, and the end down to a sink. Then I just turn on the hot water from time to time till the water coming out hot at the end. The hot water in the pipe will keep the tank warm. It might use up lots of water? But sound easy enough to keep operating it that way during the day. Does it sound like a reasonable plan? What do you think?

 

[jda]

The PEX will probably insulate it too much for heat transfer.

Do you have a car inverter that can power a heater?

 

[vetteguy53081]

Careful adding hot water which can soften/weaken tank silicone sealant

 

[ReefBeta]

The PEX will probably insulate it too much for heat transfer.

Do you have a car inverter that can power a heater?

I don't have a car inverter. I run a tesla and can't really use it to power anything. I can get a car battery and a charger as backup. But from my calculation, that won't run a heater for very long without a combusting engine.

Will there be other type of tubing more suitable for heat exchange?

 

[ReefBeta]

Careful adding hot water which can soften/weaken tank silicone sealant

The hot water will not go into the tank, only flow through the pipe. The pipe is submerged in the tank. The heat should be nowhere near the tank's silicone I think.

 

[KevPool]

this may be just the Canadian in me speaking but what about putting a bunch of hot pocket glove warmers into a zip lock bag they usually give about 4 hours heat for your hands, I wouldn't use a thin bag use a freezer grade one

 

[Gablami]

I have a Tesla too and bought two of these just in case. 300W continuous use.

 

[ReefBeta]

this may be just the Canadian in me speaking but what about putting a bunch of hot pocket glove warmers into a zip lock bag they usually give about 4 hours heat for your hands, I wouldn't use a thin bag use a freezer grade one

It won't do much for a 180 gallon tank ... I actually taped two to a 10 gallon QT I am running. Didn't raise the temperature for even a degree.

 

[ReefBeta]

I have a Tesla too and bought two of these just in case. 300W continuous use.

Oh, does the car battery actually powering it? I thought only the lead-acid battery will be powering the 12v power when the car is not running. How long did that run for you?

 

[KevPool]

It won't do much for a 180 gallon tank ... I actually taped two to a 10 gallon QT I am running. Didn't raise the temperature for even a degree.

oh mang that's a lot of water to keep warm. yeah you need a good backup plan.

 

[Malcontent]

PEX is used in under floor radiant heating so it can't be that bad.

 

[tsouth]

Your hot water idea is sound, but I don't know how efficient it is. If you were able to siphon water from the tank, through a metal tube that's reef safe, have it coil a few times, and then run a flame against the coil, and then back into the sump, I think that'd work really well.

Rather than using plastic bags, why not use larger glass or plastic containers that are water tight. You could use alcoholic or propane burners to heat the water over the stove, and then place the water in a glass container that has a locking lid, think lid lock tupperware. Placing a few of these like blocks in your sump I suspect would most definitely work.

Aside from that, I looked into UPS and Battery back ups, and it seems that with the draw rate on heaters for a 180 gallon, they would only be able to run for 3-5 minutes max :/ I think the propane stove is much more feasible.

 

[Gablami]

Oh, does the car battery actually powering it? I thought only the lead-acid battery will be powering the 12v power when the car is not running. How long did that run for you?

I did test it with a 150W heater in a bucket so I know it works, but have not tried it long term (not many outrages where I live). My understanding is that the car monitor. it’s 12v battery and keeps it charged with the big driving batteries. Upon more research on Tesla forums, they recommend limiting the cigarette port to 15A (so about a 150W heater) otherwise risk popping a fuse.

 

[cvysochin]

We use pex loops to heat our 2000+ gallon system year round. 4 loops, tied into a tankless hot water heater with an elaborate recirculator/heat exchanger/closed system. Havent used an electric heater for years. Although it will waste some water, your plan will work.

 

[DaddyFish]

A key factor in your plan is to make sure you can position the coils of tubing deep inside the tank, near the bottom. Let the natural convection flow move the colder water near the bottom to the surface. Don't place the coils near the surface. Maybe wrap the tubing with some plastic cross stitch fabric to make everything hold shape and position? Something like this DIY breeder basket that I make for fw?

If you used 1/4" tubing (like RO systems) and include a flow restrictor, that would allow you to open the hot water faucet all the way and have a predictable flow rate through the heating system.

Play with the setup and see what you get.

 

[ReefBeta]

We use pex loops to heat our 2000+ gallon system year round. 4 loops, tied into a tankless hot water heater with an elaborate recirculator/heat exchanger/closed system. Havent used an electric heater for years. Although it will waste some water, your plan will work.

awesome. I'm ok with wasting some water since it's only an emergency plan, shouldn't be needed more than once a year, well hopefully ...

So 4 loops are enough to heat your 2000+ gallon system? Mine is 180 gallon, was planning to put like 30 ft of the tube in the tank. But the water mostly will not be flowing, only flushing it occassionally, so it make sense to have more tube inside I guess?

Is your system plumb into your house's hot water line, or the tankless heater is only for the tank? What do you use control the recirulation/temperature? Turn on a recirculation pump when need heat? or a solenoid valve?

 

[ReefBeta]

A key factor in your plan is to make sure you can position the coils of tubing deep inside the tank, near the bottom. Let the natural convection flow move the colder water near the bottom to the surface. Don't place the coils near the surface. Maybe wrap the tubing with some plastic cross stitch fabric to make everything hold shape and position?

If you used 1/4" tubing (like RO systems) and include a flow restrictor, that would allow you to open the hot water faucet all the way and have a predictable flow rate through the heating system.

Play with the setup and see what you get.

Ah good point! I was thinking about using directly a 100ft 3/4" pipe. But 1/4" does sound like a better idea.

Hold the coils down is so that the heat can be distributed throughout the tank, right? Since circulation will be taken care of by the MP40 with battery, I think it's less of a problem, or is it?

I do have glass top for the tank. I usually use screen. This time I also took the glass top out to replace the screen during outage. Helped somewhat to keep the heat in.

Also I have two tanks, a 180G and a 42G. I was thinking to run one tube, from faucet -> 180G -> 42G -> sink. If use the continuous small flow, the heat in the second tank will be a lot less than the first one, I think. It would need separate round for the two tank in this case, right?

 

[cvysochin]

Yep, you're on the right track. We used 1/2" Pex-Al-Pex as the oxygen barrier was important in our configuration. For your configuration and setup, it won't matter. Any pex will work. The larger your coil, and the thicker the diameter, the more thermal mass you will have. Like you said, you won't be recirculating it continually, but only turning it on occasionally.

If you really want to make it efficient, put some quick connect fittings on your water heater, connect an energy efficient recirculator to your hot water heater, hook up your pex, and just run it as needed. That way you won't waste any water. You'll need a battery backup or inverter to run the recircular. The taco recirculator we use consumes only roughly 17 watts on speed 3 when running.

Our system is pretty complex and tied into a hybrid open/closed loop with a brass plate heat exchanger on a tankless water heater on our dedicated fish room building. We use multiple recirculators tied into multiple Apex probes with individual inkbirds for redundancy. 1 watt of electric heat = 3.41 BTU, so a 500 watt electric heater in your sump is 1705 BTU. Our heating system is on another level and generates 30,000-40,000 BTU of heat, so it was critical to have redundancies in place.

 

[DaddyFish]

Ah good point! I was thinking about using directly a 100ft 3/4" pipe. But 1/4" does sound like a better idea.

Hold the coils down is so that the heat can be distributed throughout the tank, right? Since circulation will be taken care of by the MP40 with battery, I think it's less of a problem, or is it?

I do have glass top for the tank. I usually use screen. This time I also took the glass top out to replace the screen during outage. Helped somewhat to keep the heat in.

Also I have two tanks, a 180G and a 42G. I was thinking to run one tube, from faucet -> 180G -> 42G -> sink. If use the continuous small flow, the heat in the second tank will be a lot less than the first one, I think. It would need separate round for the two tank in this case, right?

People are going to get sick of me touting this stuff... but it's a cheap and effective way to have an insulative top that you could drill holes into, small cutouts etc. I'm envisioning this whole setup ready to drop into place, tucked into a closet somewhere for that inevitable day.

 

[cvysochin]

Here's a visual.