Heating large tanks with your gas hot water heater. Save 40% on energy cost!

[Bob E]

Great write up, Thank you

 

[rygh]

... I use an in sump Titanium coil (1/3HP). My setup as follows.

Great find on that coil !!
I assume (hope) they used titanium on those welds also.

 

[anit77]

Could the coil, especially the one from Fish-Street, be used to also cool the tank in the summer?

 

[DBR_Reef]

Could the coil, especially the one from Fish-Street, be used to also cool the tank in the summer?

Yes- it appears that the fish street coil is designed to be hooked up to a conditioning unit and filled with refrigerant. If this is a little past your ability then you could also run a coolant through it that exchanges heat with a AC condensing coil.

 

[splix]

I dont know. I'd be a bit worried about that heat exchanger. One tiny internal leak between chambers and you're pumping sink water into your tank. You wouldnt even know it until it's too late either.
I'd rather have a heater fail and apex catch it. Seems less risky. By the time the salinity monitor caught the salinity change, your tank is already full of city water.

Insulate your sump and I bet you'll be surprised in the difference in heater usage. I live in a cold winter climate and had a basement sump.

 

[DBR_Reef]

I dont know. I'd be a bit worried about that heat exchanger. One tiny internal leak between chambers and you're pumping sink water into your tank. You wouldnt even know it until it's too late either.
I'd rather have a heater fail and apex catch it. Seems less risky. By the time the salinity monitor caught the salinity change, your tank is already full of city water.

Insulate your sump and I bet you'll be surprised in the difference in heater usage. I live in a cold winter climate and had a basement sump.

Insulating definitely helps, but most heat loss is due to evaporation, and without covers this is hard to control, and covers reduce light and gas exchange.

I'm going to have to strongly disagree with you as to it's tank safety- a weld seam failure is incredibly unlikely, and the only real way it would happen is if there was corrosion at a weld due to improper welding, which is easy to check for. I don't know if you've seen what a leaking heater can do to a tank, but electrolysis, copper contamination, and glass shattering are all common. If you install a ground probe (which I consider a necessity), then a gfi trip can shut down your entire tank. A hot water heater gives you the chance to remove the last of the 120v sources from your tank.

If a leak is something you were worried about, with either heat exchanger, then a high sump level switch that shuts off the heater could easily be programmed with a tank controller, and is something many of us already have as a safety for our ATO's. Lets say it dumps a few gallons before the tank controller catches it, all that would happen is is a slight drop in salinity. A little bit of tap water definitely wouldn't hurt the tank.

 

[splix]

Insulating definitely helps, but most heat loss is due to evaporation, and without covers this is hard to control, and covers reduce light and gas exchange.

I'm going to have to strongly disagree with you as to it's tank safety- a weld seam failure is incredibly unlikely, and the only real way it would happen is if there was corrosion at a weld due to improper welding, which is easy to check for. I don't know if you've seen what a leaking heater can do to a tank, but electrolysis, copper contamination, and glass shattering are all common. If you install a ground probe (which I consider a necessity), then a gfi trip can shut down your entire tank. A hot water heater gives you the chance to remove the last of the 120v sources from your tank.

If a leak is something you were worried about, with either heat exchanger, then a high sump level switch that shuts off the heater could easily be programmed with a tank controller, and is something many of us already have as a safety for our ATO's. Lets say it dumps a few gallons before the tank controller catches it, all that would happen is is a slight drop in salinity. A little bit of tap water definitely wouldn't hurt the tank.

All valid points. I'd have to agree with you on that.

 

[Outdrsyguy1]

Great post. Thanks for such good detail and links to equipment needed!

 

[brownsalt92]

Awesome discussion, will be implmenting this on my tanks in the future

 

[Muttley000]

I am using the pex method for heating my 1600 gallon system with a ranco temp controller and a bronze re-circulation pump and my Apex acting as a backup over-temp controller. My radiant heating system runs everyday at least once even during the summer months so I am not really concerned about stagnant water in the loop but if it only ran a couple of times a week I would definitely have a concern about bacteria. Cost wise I was between $300-$400 for the pex system I installed largely because of the cost on the bronze re-circulation pump and the Ranco controller. I agree that using a hot water heater on larger tanks is more efficient and safer than using electric heaters.

I think the failure risk is on par with a pex system which is minimal with backup temp controllers and good plumbing connections.

What is your temperature delta between the water entering the heat ex-changer vs leaving the heat ex-changer when you use this method for heating?

Sounds like our systems are very similar with the dance, apex and bronze pump. My sump is a 270 gallon plywood build, so plenty of room in there for the Pex coil, all connections well away from the sump and insulated on the hot side. My whole system is in the basement, so even in the summer it runs at least once a day. I've been running it for a few years now problem free!

 

[jschultzbass]

This may be a stupid question, but why do you need the circulation pump on the hot water line? Wouldn't the house pressure be enough to push it through the system?

 

[DBR_Reef]

This may be a stupid question, but why do you need the circulation pump on the hot water line? Wouldn't the house pressure be enough to push it through the system?

Your house works by pressure differentials- with high pressure flowing to low pressure. Inside the supply line and all plumbing in your house, there is pressure (lets say 60 psi). When you open your faucet, you release pressure, the pressure at the faucet is close to zero, and the water flows from high to low pressure. When we make our loop from a hot water line, through the heat exchanger, and back to the cold water supply line for the hot water tank, the inlet and outlet of that loop have approximately the same pressure, so water stays stationary.
In fact without the circulatory pump, We might actually have water flowing the wrong way if we have the hot water turned on elsewhere in the house, as the heating loop can act as a second hot water pipe- only it will be carrying cold water, which will cool your tank instead of heating it.

 

[jschultzbass]

Your house works by pressure differentials- with high pressure flowing to low pressure. Inside the supply line and all plumbing in your house, there is pressure (lets say 60 psi). When you open your faucet, you release pressure, the pressure at the faucet is close to zero, and the water flows from high to low pressure. When we make our loop from a hot water line, through the heat exchanger, and back to the cold water supply line for the hot water tank, the inlet and outlet of that loop have approximately the same pressure, so water stays stationary.
In fact without the circulatory pump, We might actually have water flowing the wrong way if we have the hot water turned on elsewhere in the house, as the heating loop can act as a second hot water pipe- only it will be carrying cold water, which will cool your tank instead of heating it.

Of course, I wasn't thinking of the pressure in the return to the HW heater. I'm setting this up on my 300 gallon for sure. Just need to decide if I'm going to run a new line from my hot water Pex manifold or "T" off an existing line by the tank.

 

[Scott.h]

Although I agree with the concept, keep in mind you will go through some hot water heaters doing this. A coworker of mine had a larger house, and decided to do do a closed loop circulating system so he had hot water on demand. Obviously the water heater worked harder, as the system acted like a giant cooling coil. He was replacing hot water heaters about every 3 years. Good ones. A cheap one will run you $500 bucks if you do it yourself. I'm not sure the energy savings would pay off, aside from the hassle. I run 3 - 250 watt heaters and one 300. My total house energy bill isn't bad, even in a Michigan basement.

 

[DBR_Reef]

Although I agree with the concept, keep in mind you will go through some hot water heaters doing this. A coworker of mine had a larger house, and decided to do do a closed loop circulating system so he had hot water on demand. Obviously the water heater worked harder, as the system acted like a giant cooling coil. He was replacing hot water heaters about every 3 years. Good ones. A cheap one will run you $500 bucks if you do it yourself. I'm not sure the energy savings would pay off, aside from the hassle. I run 3 - 250 watt heaters and one 300. My total house energy bill isn't bad, even in a Michigan basement.

Well I certainly hope it won't be that bad. I did a quick internet search and didn't find any complaints about recirculating systems killing hot water heaters, but that doesn't mean it doesn't happen. Hopefully your buddies was a anomoly. My impression was that heater lifespan was more dependent on water chemistry than heating load, but I may be wrong on that. It shouldn't be a problem for on demand hot water heaters, but I'll have to wait and see about a tanked system. Hopefully one of the people who have been running one of these systems for longer can chime in as to if it shortened their hot water heaters lifespan. I think that these systems should be less load on the heater than most hot water re-circulators though.

A quick calculation: for a uninsulated pipe with a 60 degree F difference between water and air (https://www.engineeringtoolbox.com/copper-pipe-heat-loss-d_19.html), we lose about 10w per foot (this is why I insulated my pipes for this system: it's about a watt per foot with insulation https://www.engineeringtoolbox.com/heat-loss-insulated-pipes-d_1152.html). So if your friend ran a un-insulated 200 ft system (100 there and back), that is the equivalent of a 2000w heater at a delta of 60 degrees (I have no idea if this is accurate in his case). But if we assume this is true, and his system reduce the lifespan of the HWH by half; and we run a 2000w equivalent heater some of the year, some of the time, we might expect a 10% shortening in lifespan. So that would be a cost equivalent of shortening the hot water heater by $50. That's $5-10 a year, which I would assume is a worst case scenario. I'm OK with that cost, but I'm hoping it's far less, as replacing HWHs is a pain.

 

[Scott.h]

Well I certainly hope it won't be that bad. I did a quick internet search and didn't find any complaints about recirculating systems killing hot water heaters, but that doesn't mean it doesn't happen. Hopefully your buddies was a anomoly. My impression was that heater lifespan was more dependent on water chemistry than heating load, but I may be wrong on that. It shouldn't be a problem for on demand hot water heaters, but I'll have to wait and see about a tanked system. Hopefully one of the people who have been running one of these systems for longer can chime in as to if it shortened their hot water heaters lifespan. I think that these systems should be less load on the heater than most hot water re-circulators though.

A quick calculation: for a uninsulated pipe with a 60 degree F difference between water and air (https://www.engineeringtoolbox.com/copper-pipe-heat-loss-d_19.html), we lose about 10w per foot (this is why I insulated my pipes for this system: it's about a watt per foot with insulation https://www.engineeringtoolbox.com/heat-loss-insulated-pipes-d_1152.html). So if your friend ran a un-insulated 200 ft system (100 there and back), that is the equivalent of a 2000w heater at a delta of 60 degrees (I have no idea if this is accurate in his case). But if we assume this is true, and his system reduce the lifespan of the HWH by half; and we run a 2000w equivalent heater some of the year, some of the time, we might expect a 10% shortening in lifespan. So that would be a cost equivalent of shortening the hot water heater by $50. That's $5-10 a year, which I would assume is a worst case scenario. I'm OK with that cost, but I'm hoping it's far less, as replacing HWHs is a pain.

Doing what you are doing I'd think a small boiler system, self contained from the rest of the house might be a good option too. And the whole system could be plumbed close to the tank. I'm thinking like the ones used in a house with radiant heat or what they use for heated concrete. Those systems are cheap to run, and I'd think they'd hold up a lot better too. But it might be costly to buy. It might be worth a call just to find out what they intail.

 

[DBR_Reef]

Doing what you are doing I'd think a small boiler system, self contained from the rest of the house might be a good option too. And the whole system could be plumbed close to the tank. I'm thinking like the ones used in a house with radiant heat or what they use for heated concrete. Those systems are cheap to run, and I'd think they'd hold up a lot better too. But it might be costly to buy. It might be worth a call just to find out what they intail.

you could certainly use a boiler, but they tend to require mixing valves, and I've seen a lot of these fail.

 

[Yam]

For our system, the recirculation pump turns on for 3 mins, ~6 times a day in the winter. Negligible imo compared to dishwasher showers, laundry, etc. Our second hot water recirculation (for instant hot water convenience at bathroom) runs on demand via remote. We press a button in the morning and it turns on for a few minutes. Same in the evening. Rather wasteful to cycle hot water 24x7 imo unless you're running a hotel, etc.

 

[siggy]

A friend used this principle (exchanger) to heat the floor in his basement bathroom, he rapped his hotwater tank in pex then covered with a HW tank blanket.
@Terence this might help with the longer run,
this is for remote boilers and have many variations and sizes

 

[Cliff Shepherd]

Following. I already have a boiler/domestic on demand hot water heater to supply both hot drinking water and to heat my floors. Will think and see what side would be better fit for a tank heater.
The only thing off the top of my head is the infloor heating has antifreeze in it as it a closed loop system.