Hot Tub Water Heater Replacement - Electric to Gas

Curious of your intentions? Gain?

What is age of electric heater, percentage of efficiency and configuration.

On demand heaters are of the 80% efficiency range.

Are you refering to replacement with a "micro-boiler" instead of an on-demand heater?

In my experience, electric on-demand heaters are generally more reliable than gas on-demand heaters, but this experience is in an environment with a very corrosive atmosphere- sea air. Also, the gas available (bottled natural gas) is sometimes of questionable quality. The most common failure of the gas units is related to corrosion, especially of the pilot port, such that it becomes impossible to keep the pilot light lit. The burners also corrode rapidly, providing uncontrollable heating. While electric units, not properly protected can suffer from corrosion of the electrical connections, this is much easier to prevent and generally does not result in a catastrophic failure of the unit. I do not know if these same constraints would apply to Chicago...

I would suggest finding out how much electricity your hot tub is using to see if the considerable investment in a gas heater would be worth it.

You can easily determine how much power you are using by wiring an electric clock in parallel with the heater. The clock will have to be an older one that has a motor to run the hands. If the heater is 110V - wire the clock right across the terminals. If the heater is 220V, wire the clock to one leg and neutral. Keep track of how much the time advances in a given period. This will give you hours. Note the kilowatt rating of your heater. Multiply these for kilowatt-hours, which your power company can tell you the cost of.

I think using something like a Rinnai is a great idea. I would take it a little further and put in a heat exchanger for the spa so that you could also use the potable on demand water for your home as well. If the electric element you have still works, I would keep it in-line as a backup. I have also seen the spa water preheated with solar collectors which would also reduce costs even further. I use the Rinnai to fill my hot tub with hot water, It should easily keep it heated as well.

I've good experience from on-demand gas heaters tough you need be particularly attentive to temperature rise per/hour ratings and size of spa (Gallons).

Electric water heaters are generally more efficient about 100%. A balboa flowthru design may suit.

As others have said its really about the cost of the change and the cost of running either system. Depending on where you are located changes the cost of Gas and Electricity.

I have a hot tub and I removed the electric heat and installed a duel loop heat exchanger. The water from the hot tub is pumped through the heat exchanger in its own loop. I then pump the hot water from my houses Domestic Hotwater tank through its own loop in the duel loop heat exchanger. My Domestic Hot water tank is a Natural gas tank and by doing this and the extra cost of the one Electric water pump is a lot less per month $ than the Electric tank heating system. But then again I am in Alberta Canada and in the winter my hot tub is used outside at -30F.

So you have to do the math before making a change, it might not be worth it or maybe it will be?

Three things come to mind

1: A large capital cost

2: Tank-less units use a lot more gas for a shorter period of time. I have informed people that their exiting gas servece can not support a tankless unit as they have maxed out their gas supply by having a gas furnace, multiple gas fireplaces, gas stove, gas dryer and big killer is the pool heater. You need to compute your max gas consumption and see if the sevice from the steet can support it. You need a bigger gas meter.

3: Will the manufacturer of choice support this application , due to the chemicals used in hot tub.

I would suggest adding solar panels to the roof of your spa to power electric water heaters. This will eliminate cost increases through raising prices of electricity and gas. The carbon cap and trade system currently being debated by the US gov will get passed some time in the near future and will raise gas and electricity prices. Now is the time to prepare for those increases.

Excellent suggestion; solar panels to heat the water and PV offset the power bill

A new natural gas tankless water heater uses 9500 to 157000 input btu with 95% efficency. How many sq. feet of solar panels would be required for this? A bunch I would imagine.

I'm surprised that no one has commented on the chemical compatibility issue. Hot tubs typically are chlorinated or brominated for bio-loading control. Stainless steels can experience galvanic and stress crack corrosion in such environments. Copper fares not much better. Use of these materials can cause premature failure. Coating of these materials with a plastic can protect them, but since they are good insulators, the heat transfer coefficient goes way down for even a thin layer, resulting in more burn time and less financial benefit.

A buddy of mine changed his spa over from electrical heat to propane. It worked well, but the financials of doing so are becoming less attractive as LP & natural gas prices go above $3 a gallon (or BTU equivalent). His spa was outside (hope yours is too) so exhaust of the combustion by products was not an issue, but watch out for where you would locate the burner and what nuisance effects might be caused by prevailing winds blowing in unwanted directions.

I did mention it in my response

Thank you all for your responses to my question. I have decided to rebuild my Hercules electric spa controller, which heating element met its end of life span. My chose was made simple impart by after reading your responses and my budget.

Thanks again

Thanks for kick start this thread; I've been meaning to get back to for an update on what I did.

When I bought the house some 5 years ago. It can with a four season built in hot tub room. My problem was every time I used it my electric bill would sky rocket. Never owning one before I assumed at first this was the price you pay to run one.

Here's what I did.

The system was a Hercules designed sometime during the 70's I think, Excellent design for it era. When I opened the panel the wiring was old brittle and devices signs of corrosion.

First,

I gutted the panel. Keeping only the stainless steel tube, thermo overload devices, air tube switches and enclosure that mounted to the hot tub water system. (I will refer to this unit as Node2).

Second,

I added a 24-24-6 NEMA box for easy accessible troubleshooting and monitoring of the system (I will refer to this as Node1).

Third,

Ran 25cont 22ga cable from Node1 to Node2 for 24Vdc IO communication.

Ran 7-10ga wires for pump, blower, heater, and ground from Node1 to Node2.

Ran thermostat wire for temp monitoring

Forth,

Upgrades in Node1

Replaced 5kw heater

Replaced water flow sensor

Fifth,

New Node2 System

Micro PLC for control and monitoring of system

3 motor control relays with high amp contacts

Temperature controller

Theory,

Sequence of controller operation:

Every hour of processor time I have pump circulate water at low speed.

Auto sets temp controller for use or standby

Controls user blower and/or pump speed

Auto Pump/blower/heater timeout for energy savings (Teenager).

Final Note:

After replacing old wiring and relay components plus adding PLC control system. I have had the system running for the last four months without concern.

I want to do the same thing, only using a 100,000 BTU propane pool heater and a new 110 v 20A Hudson Bay from Home Depot. I don't have much choice as I am off grid and rely on solar. I can run the pump okay, but don't have enough to run the heater. I just want to tap into the tub heater plumbing and run the heater from the tub control panel. Feasible?