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Fastest & Cheapest Way To Heat Your Spa


Str8rippin

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So Just bought a Hot Tub/Spa and i fired it up and it took over 8 hours to get to 35 Degrees Celcius (95 degrees Farenheight)

I Figured this is rediculous so i worked out a way to heat it much quicker and without using any power apart from pump Power (No Heating Element)

All I Have done is bought a Rinnai Tankless/Instantanous LPG Hot water heater off ebay for $300, Connected it to a 9KG BBQ Gas Bottle, And Run Garden Hose From The Pressure side of the pump into the Inlet, and out of the heater into the suction side of the pump.

The Water heats up within 1 Hour to over 100 Degrees, I Have An Rinnai Electronic Controller which keeps it heating at 42 Celcius (110) farenheight.

This Uses little Gas Being a 5 & and half star gas rating unit, And i only need to have it on for 1 hour then i can either use the old slow electric one to keep it warm or occasionaly turn it on again to pump Hot water straight in.

Reasons Why this is alot better than ANY other Type of Spa/Pool Heating

1. Gas Bottle = Know how much your spa is costing and how cheap is gas?

2. From Cold to Hot in 60 Minutes (Beat That Electric Element)

3. Whole Setup Cost Under $550 Or you can a Normal Spa GAS Heater From Pool Shop Start At Around $1500 NO THANKS!

4. Power Bill at End Of Month = :) inted of :@

5. Breaks Down? Easy to repair/replace Domestic Tankless Water Heater

NO The chlorine will not damadge the Unit,

Heres Some Picys Of The Setup Oh And Added Cd Player

img20141c.jpg

img20151.jpg

img20161s.jpg

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So Just bought a Hot Tub/Spa and i fired it up and it took over 8 hours to get to 35 Degrees Celcius (95 degrees Farenheight)

I Figured this is rediculous so i worked out a way to heat it much quicker and without using any power apart from pump Power (No Heating Element)

All I Have done is bought a Rinnai Tankless/Instantanous LPG Hot water heater off ebay for $300, Connected it to a 9KG BBQ Gas Bottle, And Run Garden Hose From The Pressure side of the pump into the Inlet, and out of the heater into the suction side of the pump.

The Water heats up within 1 Hour to over 100 Degrees, I Have An Rinnai Electronic Controller which keeps it heating at 42 Celcius (110) farenheight.

This Uses little Gas Being a 5 & and half star gas rating unit, And i only need to have it on for 1 hour then i can either use the old slow electric one to keep it warm or occasionaly turn it on again to pump Hot water straight in.

Reasons Why this is alot better than ANY other Type of Spa/Pool Heating

1. Gas Bottle = Know how much your spa is costing and how cheap is gas?

2. From Cold to Hot in 60 Minutes (Beat That Electric Element)

3. Whole Setup Cost Under $550 Or you can a Normal Spa GAS Heater From Pool Shop Start At Around $1500 NO THANKS!

4. Power Bill at End Of Month = :) inted of :@

5. Breaks Down? Easy to repair/replace Domestic Tankless Water Heater

NO The chlorine will not damadge the Unit,

Heres Some Picys Of The Setup Oh And Added Cd Player

img20141c.jpg

img20151.jpg

img20161s.jpg

congrats on your new hot tub- enjoy it!

I am going to skip through some of the math and give you the answer.. A 20lb bottle of propane commonly filled to 18lb holds the equivalent of 110 KWh of electric heating potential (expressed in BTU equivalents, assuming both are 100% efficient). That 20Lb bottle is $20-$25 if you buy a Blue Rhino exchange, probably $15 if you have it refilled yourself at a station. Assuming $4/gal. That is the equiv of $0.18/KWh, assuming that 100% of the heat from that $20 bottle makes it to your tub's water column (which it won't). I pay $.09/KWh, so for me your solution would be 2x as expensive even if I captured every single BTU.

I'd be curious what the flue efficiency of your water heater is (I think most tankless are 75%).. Assuming no losses through the garden hose setup you have, this means 25% of the heat you are producing goes up the water heater chimney. Which makes the electrical equivalent somewhere around $.24/KWh. Well above the Nat'l Average.

For all practical purposes, electrical heating is 99-100% efficient in a hot tub application. Negligible loss there.

So you are heating your tub faster, but you likely aren't saving any money, unless you get propane for very low $$ or your electricity is very high $$.

Where you WILL save some money is by putting some insulation in that tub.

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Yes, insulation and a decent cover will save you more money in 6 months than you paid for the rennai, also be certain the water hitting your PVC is less than 110F or you will risk serious damage to your entire tub.

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Yes, insulation and a decent cover will save you more money in 6 months than you paid for the rennai, also be certain the water hitting your PVC is less than 110F or you will risk serious damage to your entire tub.

LOL, exactly. He can pat himself on the back all he wants for the method to heat the spa quickly and efficiently but he's ignoring the main issue which is that poorly insulated hot tub (and I hope there is an actual cover to it). That's the reason it was heating slowly and his Power Bill at End Of Month = :( instead of :).

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Refreak, you seem to know your costs, here in Australia electricity is expensive and the only off peak rate is for electrical hot water and slabheating. Let's talk estimation by experience, my spa uses 2.5 kilowatts every hour so 24c x 2.5 = almost 75c, per hour, considering it will be heating 4 hours a day that's $3 per day? x that by 7 and add a few hours to get it very hot before you use it = over $20 per week.

I've heated mine more than 5 times and I still have not ran out of gas, I only use it 1ce maybe twice a week so less than $10 per week max? Please correct me on this

Also how do you think I should insulate it apart from the new cover that's arriving tommotow I purchased from austspacovers.com.au and putting the side panels back on?

Thanks guys.

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LPG = 95,500 BTU/gallon

95500 BTU = 27.96kW electricity

As stated earlier, electric heating is close to 100% efficient (1kW of electric put into the heater will put 1kW into the water). Gas is NOT 100% efficient.

so........... assuming 85% efficiency with LPG, which costs less;

1 gallon of LPG or 23.7kW of electricity?

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I don't understand how it doesn't make sense, all this efficiency Mumbo jumbo is irrelevant to my costs, like I said over. $20 week for electricity under $10 for the gas setup, when i get natural gas hooked up to it it's going to be even cheaper, 23.7kw x 20c = $4.74

Or 1 gallon of lpg = under $2

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I don't understand how it doesn't make sense, all this efficiency Mumbo jumbo is irrelevant to my costs, like I said over. $20 week for electricity under $10 for the gas setup, when i get natural gas hooked up to it it's going to be even cheaper, 23.7kw x 20c = $4.74

Or 1 gallon of lpg = under $2

There are two issues here that folks aren't used to (and are driving the responses to the thread)... 1. If you only use the tub a couple of times / wk, it might make economic sense to heat on demand and not worry about the insulation. Most people keep their tubs hot all the time on this board (but there probably IS an economic argument to do exactly what you're doing from some usage patterns) 2. If the costs of LPG and/or Natural Gas is cheaper than the an equivalent amount of electric, given energy costs where you live, it makes sense to do the gas thing. It's rare that it works out that way in the US though.

More on issue #1. A well insulated tub shouldn't cost much more than $10/wk in electricity that you're estimating as gas costs- to keep it warm all the time. And with the tropical plants I see on your patio I'm guessing that it doesn't get that cold wherever you are. But the costs of getting that insulation in that tub are probably more than the value of the tub itself. You're talking about 3-400 for a good cover, and more than that for a foam fill of the entire cavity (look for spray foam insulation contractors and get a quote to fill the whole cavity except for the area right around the motors / control equipment).

More on issue #2. If you're interested in evaluating your energy decision further, it's more precise to look at it in terms of the physics of the energy that it takes to heat a given amount of water, and compare relative costs of different methods to provide that energy (electric, gas, etc.). This would give you a much better perspective than anecdotal observations on how many bottles of LPG you are using. I'm still skeptical that LPG is cheaper (and/or your ROI on the setup will take a very long time), but what you're telling me in terms of energy costs suggest that from a physics perspective the reltative costs are probably about the same or maybe favor a gas approach slightly. The reason you're saving money is because the insulation (mentioned in #1) is so poor that you're losing heat because the electric heater can barely overcome the loss of the tub from lack of insulation.

Or to put it another way, You're "nuking" the tub with your gas setup to get it to temp FAST, and it rapidly cools due to lack of insulation. You could probably have done the same thing with a massive (10-15KW) electric heater, and enjoyed similar savings. Or you could have insulated the whole thing and saved the same amount of $$. So what you did was creative, and works well for your use case.. But is fairly unconventional b/c most folks go for the insulation route and just don't worry about it. Hope this helps.

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