Spa Insulation

[downrange]

Hi all!

I am new to all this. I have been in the market to buy a hot tub. I have been to several dealers and i am starting to recieve so much information that i am not sure what is good an bad. I guess my main concern is the insulation. Some swear that a 100% insulation around the tub is the only way to go. Others say that just creates a disaster when something needs to be worked on. and that it only needs about two inches on insulation on the tub itself and maybe some on the skirt on the inside. after all heat rises and all you need is a good cover. I hear pros and cons of both. I have been looking at Lime Light Pulse made by Hot springs. that one seems to have most everyting i am looking for. IS there any pro or cons about this brand of tub? thanks!

[ps558]

Hi all!

I am new to all this. I have been in the market to buy a hot tub. I have been to several dealers and i am starting to recieve so much information that i am not sure what is good an bad. I guess my main concern is the insulation. Some swear that a 100% insulation around the tub is the only way to go. Others say that just creates a disaster when something needs to be worked on. and that it only needs about two inches on insulation on the tub itself and maybe some on the skirt on the inside. after all heat rises and all you need is a good cover. I hear pros and cons of both. I have been looking at Lime Light Pulse made by Hot springs. that one seems to have most everyting i am looking for. IS there any pro or cons about this brand of tub? thanks!

Hot Springs make a good spa. The insulation debate will never end. Yes they all have pros and cons. If you stick with a main manufacture you get a good spa.

[wylekioti]

Hi all!

I am new to all this. I have been in the market to buy a hot tub. I have been to several dealers and i am starting to recieve so much information that i am not sure what is good an bad. I guess my main concern is the insulation. Some swear that a 100% insulation around the tub is the only way to go. Others say that just creates a disaster when something needs to be worked on. and that it only needs about two inches on insulation on the tub itself and maybe some on the skirt on the inside. after all heat rises and all you need is a good cover. I hear pros and cons of both. I have been looking at Lime Light Pulse made by Hot springs. that one seems to have most everyting i am looking for. IS there any pro or cons about this brand of tub? thanks!

I am looking to buy a hot tub also and see no reason for "Full Foam" and am trying to avoid this in a tub. Heat loss from the shell of the tub should be about 1/3 of the loss from the water serface, where a good cover will do more good to make the spa less expensive to run. All I see with the full foam on the shell doing is making the tub quieter and creating problems for repairs in the future. I have not found a tub that I "fit in" yet. I plan on looking at Hot Springs to see what they offer because they are one of three brands offered within short distance where I live, but have only looked at the web site so far. I am a bit skeptical of the Moto-massage jet, saw the insides of one, looks like too many things to go wrong.

[spatech (the unreal one)]

I am looking to buy a hot tub also and see no reason for "Full Foam" and am trying to avoid this in a tub.

A high energy bill is one reason. Thermo pane works well in theory but too often it just isn't pulled off by most of that type manufacturer as they don't seal off the cabinet and their is air transfer and then we see people come on this site bumming at their $100 monthly increase in their power bill. Personally I'd stick with full foam by one of the major manufactuers like Hot Spring, Jacuzzi, Sundance, Caldera, Marquis, D1... or Arctic. With the good manufacturers you will very rarely have a need to break into that foam.

[Roger]

All I see with the full foam on the shell doing is making the tub quieter and creating problems for repairs in the future.

When 99.9 percent of all repairs are in the equipment area what sort of problems do you see the foam causing? Because a good tech can diagnos and repair a foam buried leak very easiely.

Don't let a particular sales pitch for a particular manufacturer sway your decision. Both kinds of insulation can work good if done correctly. Stick with a major manufacturer backed by a quality dealer and insulation or repairs will not be an issue. And first and formost get whats comfortable on your backside.

[Dr. Spa]

Ladies and gentlemen, "HEAT" does NOT rise! A "substance", such as air or water, when heated, will rise when it is within more of that same substance which is cooler. This is because as something is heated, it expands, and therefore becomes lighter per volumetric measure than the same substance at a lower temperature. This is called CONVECTION. Once that substance hits a barrier, it STOPS rising. A spa cover is a barrier. A spa shell is a barrier. Once it hits a barrier, heat move through the barrier by means of CONDUCTION. Heat will conduct sideways (through the side of the spa) almost as easily as it will conduct upwards (the side of your spa). FYI, heat CONDUCTS downwards quite easily as well (why do you think the floors of homes are insulated???)

[spatech (the unreal one)]

after all heat rises and all you need is a good cover.

How did I miss that? Good response Doc.

A spa with a good cover and poor insualtion on the sides is like someone going out in cold weather with a winter hat but accompanying it with shorts and a t-shirt.

[Dr. Spa]

Or your attic insulated to R-100 and your windows left open.

[wylekioti]

Ladies and gentlemen, "HEAT" does NOT rise! A "substance", such as air or water, when heated, will rise when it is within more of that same substance which is cooler. This is because as something is heated, it expands, and therefore becomes lighter per volumetric measure than the same substance at a lower temperature. This is called CONVECTION. Once that substance hits a barrier, it STOPS rising. A spa cover is a barrier. A spa shell is a barrier. Once it hits a barrier, heat move through the barrier by means of CONDUCTION. Heat will conduct sideways (through the side of the spa) almost as easily as it will conduct upwards (the side of your spa). FYI, heat CONDUCTS downwards quite easily as well (why do you think the floors of homes are insulated???)

Ok, I saw this and feel I must throw in my 2 cents. Hot tubs and spas are filled with water and air which permit convection. Conduction rate of heat depends on the barrier material. Insulation is to inhibit both of these by slowing or stopping air movement within a material with low conductivity of heat. Air movement is the greatest source of removing heat from an object like a spa, house, your body (unless you jump into a frozen river but if your spa goes for a swim... ) Movement of a fluid increases heat transfer where there is a difference in tempurature. Convection creates movement in a fluid (liquid or gas). Simply, you are right, but, in a tub of water, convection will move the heat to the air over the water faster than the conduction of heat through the spa shell. The cover while in use, will, provide a barrier which if sealed will now use insulation to slow the heat loss from the convection in the air. In laymans terms, heat rises through convection in a fluid and that is what is in a spa. Note your insulation in your house, two times the R value is required above compaired to the sides. Many homes do not have insulation in the floor, they sit on dirt with a concrete slab which acts as insulation and so do alot of spas. Put a pan of water on the stove and watch the vapor take the heat away, now how close to the sides of the pot can you put your hand and feel the same heat that you feel one foot above. The heat coming off the sides goes in what direction eventually? UP? We ARE working with fluids. Convection matters. Air movement matters. Spa insulation makes a difference, but the cover is the most important aspect of retaining heat, then how the rest is insulated. If your spa could have a full foam R factor of 30 and if the cover leaks or is saturated with water, reducing the R value, what good is the ubber side insulation?

The greater the tempurature differential, the greater the convetion. If you live where it is 100 degrees, you would not have the issue with loosing heat that a person who lives where it is 40. The bigger the temp difference, the faster the fluid movement through convection. The faster the fluid moves, the faster the heat can be transfered to the colder substance ( air, cover, shell, whatever) Yes, the shell needs insulation, tight cabinet, etc to prevent heat loss there but I have seen on this forum links to testing where full foam name brand spas have less than a R10 which is way less that what is required in home walls. One dealer I talked to, told me how well the spa was insulated (full foam and wrapped) and it came with a 2 inch thick cover and he had no idea what the R value was. What is the point of that?

[Hillbilly Hot Tub]

All I say is Amen.

[spatech (the unreal one)]

Yes, the shell needs insulation, tight cabinet, etc to prevent heat loss there but I have seen on this forum links to testing where full foam name brand spas have less than a R10 which is way less that what is required in home walls. One dealer I talked to, told me how well the spa was insulated (full foam and wrapped) and it came with a 2 inch thick cover and he had no idea what the R value was. What is the point of that?

I've seen spas with good covers but poorly insulated sides, I’ve also seen spas that are well insulated on the sides but have thin/low-density covers. Any truly energy efficient spa will have a well insulated cover as well as being well insulated along the sides and the bottom. We obviously don't need to decide which area is the most important because they all are.

[Tom]

a concrete slab which acts as insulation....

Uh, well, no....

Concrete has an insulation value of about 0.2 per inch which ain't gonna keep you warm on a cold winter night. When you're camping, you'll stay a lot warmer on a pad of closed-cell foam than you will on bare ground or a concrete pad. Boy Scouts of America used to advise three layers of insulation under you for each layer over you for winter camping (may not be current with improvements in sleeping bag technology).

Cold ground is a giant heat sink that sucks heat down. Cool climate spas need insulation on the bottom (however it's done)

[wylekioti]

a concrete slab which acts as insulation....

Uh, well, no....

Concrete has an insulation value of about 0.2 per inch which ain't gonna keep you warm on a cold winter night. When you're camping, you'll stay a lot warmer on a pad of closed-cell foam than you will on bare ground or a concrete pad. Boy Scouts of America used to advise three layers of insulation under you for each layer over you for winter camping (may not be current with improvements in sleeping bag technology).

Cold ground is a giant heat sink that sucks heat down. Cool climate spas need insulation on the bottom (however it's done)

Ok, so I worded that poorly. Yes you are right Tom. For that kind of heat transfer that you are talking about, the shell would have to sit on the concrete. I dont think spa manufacturers do that. Dirt, however, has been used as an insulation. See: Root Cellars. As I said the larger the difference in temp.. the faster the heat transfer.. so on Cold ground.... but we are not talking about camping. (we could go into where your body hits the ground due to weight makes better contact increasing heat transfer over the parts that are touching the ground without the contact pressure)

Going back to an earlier post about loosing heat from your body without proper clothing. Water (sweat) and air is what keeps your body cool. Put a fan blowing on you and you get cooler. This is what happens with water to air heat transfer just like you have in your spa, thus the need for a good cover to help hold heat in.

My point was just (to avoid the argument of what is better way to insulate a spa) that if you are worried about cost of heating, a good cover vs poor cover, will do as much or more than the difference in insulation in most name brand spas. That is not to say there may not be a real looser or a far better insulated tub. But until all brands of spas are tested on equal ground with conditions that really test the insulation and tightness of the spa.. the world may never know.

[Trigger]

Hi all!

I am new to all this. I have been in the market to buy a hot tub. I have been to several dealers and i am starting to recieve so much information that i am not sure what is good an bad. I guess my main concern is the insulation. Some swear that a 100% insulation around the tub is the only way to go. Others say that just creates a disaster when something needs to be worked on. and that it only needs about two inches on insulation on the tub itself and maybe some on the skirt on the inside. after all heat rises and all you need is a good cover. I hear pros and cons of both. I have been looking at Lime Light Pulse made by Hot springs. that one seems to have most everyting i am looking for. IS there any pro or cons about this brand of tub? thanks!

"All heat rises" So by that logic, you wouldn't even need insulation on the sides? Yes Hot AIR rises, heat transfers out from hot to cold. (thermal equilibirum)

A good cover is important. but is not the only issue.

Thermal pane insualtion can work but it is expesensive and must be done right. very few tubs do it rihgt and there are trade offs for a Thermal tub.

Full Foam insualtion does indeed work and I believe the better of the two options available.

The number one manufacter of hot tubs in the world uses full foam and has done so for years. Don't belive me, ask folks who own them. Google. Search. Seek out. If full foam was the absolute nightmare some dealers would have you belive, Hotsprings, Caldera, Sundance, D1, etc would be out of buisness.

The only folks claiming full foam is bad are salesmen who claim that concrete is an insulator, and all heat risese and all you need is a good cover.

Get it? it's a sales ploy to scare you.

[wylekioti]

a concrete slab which acts as insulation....

Uh, well, no....

Concrete has an insulation value of about 0.2 per inch which ain't gonna keep you warm on a cold winter night. When you're camping, you'll stay a lot warmer on a pad of closed-cell foam than you will on bare ground or a concrete pad. Boy Scouts of America used to advise three layers of insulation under you for each layer over you for winter camping (may not be current with improvements in sleeping bag technology).

Cold ground is a giant heat sink that sucks heat down. Cool climate spas need insulation on the bottom (however it's done)

Ok, I did do some research, because I am not an expert on concrete or its properties. It is not an insulation, but it has a High Thermal Mass which compaired to many substances does not allow heat to travel through it quickly. It tends to store heat. Heat moves through it very very slowly. Here are some examples of the Thermal Conductivity of various substances for comparison:

Copper 918

Gold 700

Aluminum 480

Dry sand 0.86

Wood, fir. with grain 0.30

Wood, fir, cross grain 0.09

Portland Cement 0.17

(expressed in: gram-calories/second/cmXcm/cm/degree C) (its what they said on the chart)

So, as compaired to a heat conductor like metals, concrete is a very poor conductor of heat. Isn't that what the purpose of insulation is? Although it is not an "insulator", heat transfer is extreemly slow. We better notify the city that the building code which requires concrete block between a wood stove and studs that concrete will not insulate the studs from the heat of the wood stove.

I am not a spa salesman, I am shopping for a spa and found this forum, getting answers to some questions and trying to help answer some from my own experience and knowledge.

PS: Just got a spa broucher which claims: "industry's finest research and development engineers" and later in the reading you find: "Since heat rises, the cover is a critical component"

should I be quiet now?

[wylekioti]

Ok, that didn't last long.

I would like to know one thing about FF spas, I am looking at some of those too. The tempurature where I live varies between the low teens (F) for a week or two to over 100 (F) in the summer. During these cold times where we might have a few months around freezing, when the pumps are not insulated and are "vented" to the out side air, what protects these expensive components from freezing up?

[Roger]

Ok, that didn't last long.

I would like to know one thing about FF spas, I am looking at some of those too. The tempurature where I live varies between the low teens (F) for a week or two to over 100 (F) in the summer. During these cold times where we might have a few months around freezing, when the pumps are not insulated and are "vented" to the out side air, what protects these expensive components from freezing up?

The 100 degree vessel full of warm water and the warm foam surrounding them protects them. Combined with a freeze protection system that circulates water through the plumbing. Unless the particular brand has a 24 hour circ pump then the heat and water movement from that along does alot. But again all types of systems are backed up with a freeze protection system that prevents damage to plumbing. And it simply is a sensor in the plumbing usually before the pump that senses temperature below say 40 degrees in the plumbing feeding the jet pump. Once that temp is reached the pump kicks on and circulates water.

[Tom]

Ok, I did do some research, ...

So, as compaired to a heat conductor like metals, concrete is a very poor conductor of heat. Isn't that what the purpose of insulation is? Although it is not an "insulator", heat transfer is extreemly slow. We better notify the city that the building code which requires concrete block between a wood stove and studs that concrete will not insulate the studs from the heat of the wood stove.

I am not a spa salesman, I am shopping for a spa and found this forum, getting answers to some questions and trying to help answer some from my own experience and knowledge.

PS: Just got a spa broucher which claims: "industry's finest research and development engineers" and later in the reading you find: "Since heat rises, the cover is a critical component"

should I be quiet now?

No, you're doing great. You're thinking it through carefully, and I respect that. IMO People who look for facts contribute a great deal more to a discussion than people who throw out unsubstantiated opinions or parrot something they've read or heard.

You've also caught on to the fact that marketing materials are usually written by people who either don't understand the science or who deliberately "dumb it down". On the other hand, materials written by the engineers are often incomprehensible to the layman. The best we can do is compromise, and as you've pointed out, some of the compromises lean more towards sales than science.

Yes, insulation is the inverse of conductance. So R = 1/k, where k is the thermal conductivity. A definition of R-Value is

here. It's a simplified measure designed for easy understanding and comparison. Darn, I lost all my materials and papers on this when my hard drive crashed. Have to build it all up again...

Thermal mass--more properly called specific heat capacity--is another issue, and is a measure of the amount of heat energy required to raise the temperature of a chunk of the stuff by a specific amount. Water has the highest thermal mass of all substances, which means it takes a lot of heat to warm up a body of water. Substances with high thermal mass are "heat sinks" because they suck up a lot of heat without warming up much themselves. That's why having an uninsulated spa on a cold concrete pad is a poor idea - heat will transfer from the spa water to the concrete, making your heater work harder to keep the water warm. So a substance with high thermal inertia or mass is not necessarily a good insulator.

But wait, if water has a higher thermal mass than concrete, why doesn't the water suck heat from the concrete? That's because of something called thermal gradient. Energy flows from areas of high concentration (warm water) to areas of low concentration (cold concrete) and unless stopped will continue to flow until the system is in balance (temperature of water and concrete are the same). The insulation under and around your spa can't stop this, but it does slow it down a lot. The better insulated the spa, the slower the energy flow down the gradient.

Wait again. The spa water isn't touching the concrete. Even if the shell has no insulation, even if there is no floor on the spa, there's still air between the concrete and the shell, and air is an insulator, right? Yes, under some conditions. A thin layer of air (some tables show as much as 1/2" but most give 1/8" as the maximum) between two thermally inert layers is an excellent insulator. It's the small pockets of air trapped between strands of fiberglass or in the bubbles of foam that makes these substances good insulators. So you have the spa shell (warm from the water), an air cavity, and the concrete. In this case, the body of air is enough to create convection currents, and the air flows around inside the cavity, constantly moving heat from shell to cavity ( the air flows roughly in a toroid, rising in the center and dropping down around the sides). In addition, heat radiates directly from the shell in all directions, and some of that heat is lost into the concrete.

In the typical TP spa, you have a layer of foam, an air cavity, and a layer of foam (maybe even some on the floor). Typically, these two layers are about 1" thick, more or less. Sounds ideal - an air cavity between two nonconductive layers. And it does work to some extent. A full-foam spa eliminates internal convection entirely and radiation down and to the sides considerably. A perimeter insulated spa uses cavity convection to recycle heat into the water (high thermal mass, remember) and reduce heater use, while stopping radiation to about the same extent as a full-foam spa (and though they suggestive rather than conclusive, there are figures to back this up).

The thermodynamics of heat loss in a hot tub is a complex and endlessly fascinating subject, at least to some of us. (Roger and I have discussed this a great deal over the years). While a good grasp of the topic is hardly necessary to the average spa shopper, many find it of at least temporary interest.

In the end, Roger will tell you, the method of insulation is not as important as the amount and effectiveness of insulation, and neither of those is as important as comfort, effective therapy, and other factors. And IMO he's right.

Should I stop now?

[Roger]

Ok, I did do some research, ...

So, as compaired to a heat conductor like metals, concrete is a very poor conductor of heat. Isn't that what the purpose of insulation is? Although it is not an "insulator", heat transfer is extreemly slow. We better notify the city that the building code which requires concrete block between a wood stove and studs that concrete will not insulate the studs from the heat of the wood stove.

I am not a spa salesman, I am shopping for a spa and found this forum, getting answers to some questions and trying to help answer some from my own experience and knowledge.

PS: Just got a spa broucher which claims: "industry's finest research and development engineers" and later in the reading you find: "Since heat rises, the cover is a critical component"

should I be quiet now?

No, you're doing great. You're thinking it through carefully, and I respect that. IMO People who look for facts contribute a great deal more to a discussion than people who throw out unsubstantiated opinions or parrot something they've read or heard.

You've also caught on to the fact that marketing materials are usually written by people who either don't understand the science or who deliberately "dumb it down". On the other hand, materials written by the engineers are often incomprehensible to the layman. The best we can do is compromise, and as you've pointed out, some of the compromises lean more towards sales than science.

Yes, insulation is the inverse of conductance. So R = 1/k, where k is the thermal conductivity. A definition of R-Value is

here. It's a simplified measure designed for easy understanding and comparison. Darn, I lost all my materials and papers on this when my hard drive crashed. Have to build it all up again...

Thermal mass--more properly called specific heat capacity--is another issue, and is a measure of the amount of heat energy required to raise the temperature of a chunk of the stuff by a specific amount. Water has the highest thermal mass of all substances, which means it takes a lot of heat to warm up a body of water. Substances with high thermal mass are "heat sinks" because they suck up a lot of heat without warming up much themselves. That's why having an uninsulated spa on a cold concrete pad is a poor idea - heat will transfer from the spa water to the concrete, making your heater work harder to keep the water warm. So a substance with high thermal inertia or mass is not necessarily a good insulator.

But wait, if water has a higher thermal mass than concrete, why doesn't the water suck heat from the concrete? That's because of something called thermal gradient. Energy flows from areas of high concentration (warm water) to areas of low concentration (cold concrete) and unless stopped will continue to flow until the system is in balance (temperature of water and concrete are the same). The insulation under and around your spa can't stop this, but it does slow it down a lot. The better insulated the spa, the slower the energy flow down the gradient.

Wait again. The spa water isn't touching the concrete. Even if the shell has no insulation, even if there is no floor on the spa, there's still air between the concrete and the shell, and air is an insulator, right? Yes, under some conditions. A thin layer of air (some tables show as much as 1/2" but most give 1/8" as the maximum) between two thermally inert layers is an excellent insulator. It's the small pockets of air trapped between strands of fiberglass or in the bubbles of foam that makes these substances good insulators. So you have the spa shell (warm from the water), an air cavity, and the concrete. In this case, the body of air is enough to create convection currents, and the air flows around inside the cavity, constantly moving heat from shell to cavity ( the air flows roughly in a toroid, rising in the center and dropping down around the sides). In addition, heat radiates directly from the shell in all directions, and some of that heat is lost into the concrete.

In the typical TP spa, you have a layer of foam, an air cavity, and a layer of foam (maybe even some on the floor). Typically, these two layers are about 1" thick, more or less. Sounds ideal - an air cavity between two nonconductive layers. And it does work to some extent. A full-foam spa eliminates internal convection entirely and radiation down and to the sides considerably. A perimeter insulated spa uses thermal convection to recycle heat into the water (high thermal mass, remember) and reduce heater use, while stopping radiation to about the same extent as a full-foam spa (and though they suggestive rather than conclusive, there are figures to back this up).

The thermodynamics of heat loss in a hot tub is a complex and endlessly fascinating subject (at least to some of us ). While a good grasp of the topic is hardly necessary to the average spa shopper, many find it of at least temporary interest.

Should I stop now?

I found it temporarily interesting, sorry, to your third paragraph................

No really there is so much involved that most of us will say that, as long as you buy a quality spa insulation should never be a deciding factor in your decision no matter how it is spun. Comfort on your backside while you sit in it and while your wallet is thinning!

kiddin Tom about the bordom aquired from your post!

[Tom]

kiddin Tom about the bordom aquired from your post!

No yer not!

I see that you replied before I even finished editing my post...

[wylekioti]

Ok. So back to the original posting. As I think all everyone is trying to say with all installations.

Assuming the tub is well insulated, a quality cover will be benificial in operating cost. Many covers from what I understand become saturated with water over time and lose the insulation factor and thus must be replaced every few years. Some one must have upgraded to a better cover and have some idea on the cost to heat difference. Seeing covers being of different thickness and matterial available from manufacturers to aftermarket.

I also assume, that like most items sold, there are high quality and low quality covers that look identical. I have read posts where controllers may look the same but are of lesser quality.. etc.. I worked in the automotive industry where there are many cases of identical items but they are not equal. You don't think the Autolite Spark Plug from Kmart is equal to one you buy at quality auto part supplier, even though they look identical in every way. Do you think GMC = Chev pickup? But I have been out of the industry for some time and now with all the outsourcing... who knows. Last I knew, GM pickup V8 engines were made in Korea.....

I was just trying to point out that for an extra few bucks, difference in price of covers, it would be well worth that upgrade unless you live in a warm to hot climate or have free electricity.

I would like to say, I have to wonder about the quality of the insulation in the spa if the manufacturer does not offer a high quality cover. Seems they should go hand in hand.

Not trying to ruffle feathers... even though they have a low thermal conductivity.

[fourrunner72]

Ok. So back to the original posting. As I think all everyone is trying to say with all installations.

Assuming the tub is well insulated, a quality cover will be benificial in operating cost. Many covers from what I understand become saturated with water over time and lose the insulation factor and thus must be replaced every few years. Some one must have upgraded to a better cover and have some idea on the cost to heat difference. Seeing covers being of different thickness and matterial available from manufacturers to aftermarket.

I also assume, that like most items sold, there are high quality and low quality covers that look identical. I have read posts where controllers may look the same but are of lesser quality.. etc.. I worked in the automotive industry where there are many cases of identical items but they are not equal. You don't think the Autolite Spark Plug from Kmart is equal to one you buy at quality auto part supplier, even though they look identical in every way. Do you think GMC = Chev pickup? But I have been out of the industry for some time and now with all the outsourcing... who knows. Last I knew, GM pickup V8 engines were made in Korea.....

I was just trying to point out that for an extra few bucks, difference in price of covers, it would be well worth that upgrade unless you live in a warm to hot climate or have free electricity.

I would like to say, I have to wonder about the quality of the insulation in the spa if the manufacturer does not offer a high quality cover. Seems they should go hand in hand.

Not trying to ruffle feathers... even though they have a low thermal conductivity.

I'm an engineer, but not this kind!

Was just thinking that the following would be a good test of insulation, and overall quality of the spa, without the use of meters or analyzing the electric bill.

1. How long does it take to heat the spa from 80 to 100 degrees on a cold day with the cover on.

2. How long does it take for the spa to go from 100 back to 80 with the cover off and heater off?

3. Repeat 1 and 2 with jets on.

Obviously the power draw of the spa in general is separable data worth knowing (e.g. while heating, while not heating, jets on, jets off, etc.)

Of course the quality of the heater will be a factor for #1, but that is still a fair test.

I would think poorly insulated spas would take forever to heat up, therefore drawing more power. And, poorly insulated spas would cool off quicker, thus needing the heater to run more often. Stating the obvious I know, but isn't this a valid (and easy) test for everyone to do and report back data on?

Disclaimer: I didn't get my first spa delivered yet, soon it will be....thus I am a NEWBIE.

Thanks, Jeff

[Tom]

Was just thinking that the following would be a good test of insulation, and overall quality of the spa, without the use of meters or analyzing the electric bill.

1. How long does it take to heat the spa from 80 to 100 degrees on a cold day with the cover on.

2. How long does it take for the spa to go from 100 back to 80 with the cover off and heater off?

I would think poorly insulated spas would take forever to heat up, therefore drawing more power. And, poorly insulated spas would cool off quicker, thus needing the heater to run more often. Stating the obvious I know, but isn't this a valid (and easy) test for everyone to do and report back data on?

Sounds like a fine idea, easy for anyone to do in his back yard!

Couple of points:

1. Define "cold day". For somebody in Florida, that might be 40F. For a Canadian, that might be -30F. "Cold day" is just a bit too vague. You can see how differences in interpretation could completely obscure some significant differences

2. To make this work, you'd have to specify an ambient temperature and also specify windless conditions.

3. How often do we lift the cover to see if the temp is at 100F? Let's say every 30 minutes??

4. Would a spa that heated quickly due to a powerful heater (rather than good insulation) necessarily represent the best energy efficiency? ( I have my own answer to that, but think about it). The 'cool down' time might be a better indicator of insulation quality.

[fourrunner72]

Was just thinking that the following would be a good test of insulation, and overall quality of the spa, without the use of meters or analyzing the electric bill.

1. How long does it take to heat the spa from 80 to 100 degrees on a cold day with the cover on.

2. How long does it take for the spa to go from 100 back to 80 with the cover off and heater off?

I would think poorly insulated spas would take forever to heat up, therefore drawing more power. And, poorly insulated spas would cool off quicker, thus needing the heater to run more often. Stating the obvious I know, but isn't this a valid (and easy) test for everyone to do and report back data on?

Sounds like a fine idea, easy for anyone to do in his back yard!

Couple of points:

1. Define "cold day". For somebody in Florida, that might be 40F. For a Canadian, that might be -30F. "Cold day" is just a bit too vague. You can see how differences in interpretation could completely obscure some significant differences

2. To make this work, you'd have to specify an ambient temperature and also specify windless conditions.

3. How often do we lift the cover to see if the temp is at 100F? Let's say every 30 minutes??

4. Would a spa that heated quickly due to a powerful heater (rather than good insulation) necessarily represent the best energy efficiency? ( I have my own answer to that, but think about it). The 'cool down' time might be a better indicator of insulation quality.

1 & 2. Good point...since we all can't control the weather, including wind, we could mention that day's avg temp and wind chill (or speed?) along with the results Even a test like this when it is 70 degrees out, is still interesting data.

3. Another good point...30 min sounds good, and if the spa overshot the temp goal, then we could interpolate the data back to what it would have likely been for 100 degrees or 80 degrees. Or just submit what happened (e.g. went from 76 to 101 in 3 hours, 30 minutes @ 50 degrees ambient)

4. Heater A is weak and spa takes twice as long to heat versus Heater B is strong and heats spa twice as fast....would all come down to power draw of the spa while heating. Obviously that information is critical but I would venture to guess that the time that the heaters are on is critical and the power draw difference is less critical dollars-wise. I could be wrong...Well, we could certainly take the heater totally out of the equation by measuring cool down time (with cover and without cover), but will that tell us how efficiently the spa can heat up...not sure...seems important

[Tom]

will that tell us how efficiently the spa can heat up...not sure...seems important

Is important, but hard to determine the efficiency without measuring power usage. Your test would bypass the need for a meter quite nicely as a measure of insulation efficiency.

And if we had an accurate (or even approximate) measure of water volume in the spa, we can adjust the figures to make them comparable (though I'm not sure how to adjust for differences in ambient temperature. Anybody?)

Fourrunner, I think it sounds like a terrific fall project!

Tom

If anybody is curious, the formula for heat loss is E = Mc(t2 - t1)/h, where

E = energy given off in cooling

M = mass of spa in kg (easy to covert from US gallons)

c = the specific heat capacity of water (4.2 kJ/L)

t2 = final temperature in Celsius (equivalent of say 80F)

t1 = initial temperature as above (to 100F)

h = the cooling time in hours.

This will give results as negative numbers (energy loss). A spa that lost 3674 kJ/h would be better insulated than one that lost 6347 kJ/h (to pull numbers at random).