Wanted High R-value

[Catch_48]

 Hello would like some imput on R-value on differant  Spa's and weather 120 or 220v is most preferable, I am considering heating tub with external means with heat exchanger from home system.
 Thanks Catch_48

[Brewman]

In general, 220 is preferable to 120.  Many spa's won't even run on 120.  
There is little out there discussing r value for hot tubs, unless you consider the cover thickness to be some measure of that.  
I'm not sure I follow what you mean by your heating comment.  How and why would you do this?  
Are you by chance asking about some type of built in spa, as opposed to a portable?  
Brewman

[drb]

Are you planning to run it off your home heating system?  If you have a hot water or steam system now, be aware of a couple issues:

(a) You may want to heat the spa when you're not heating the house -- that will affect the efficiency of your home unit in a big way.

(b) You can't use just anything for the heat exchanger.  Steel and copper - even some types of stainless - will croak in short order.  I'd plan on a good stainless or cupronickel.  Your spa sanitizing chemicals are much more agressive than plain water...

R-value:  If your tub has an R-10 (roughly 3 inches of foam, give or take) and a surface area (the bowl part, towards the cabinet - not the water area) of 100 square feet, and it's 20 degrees outside, it will take about 250 watts to maintain that heat level.  If you're paying $.10 per kWh, that's $17.71 a month.  If you increase the R-value to 20, you're saving $8.85 a month...  but only when it's 20 degrees all month.  If it gets to be 65 degrees outside, now you're saving $4.43 a month.

Keep in mind, as posted previously, that this is only the standby loss thru the walls of the tub, and doesn't include losses thru the cover or by blowing cold air in thru the jets.

[Chas]

Wow, some good info.

I would add that I have many people who come in looking to put together a real special system that uses solar, domestic water heater(s), home hydronic system, steam, or whatever - all in a search for a spa that will not eat them out of house and home on the electric bill.

The funny thing is that most of the name-brand tubs have good energy designs, and even though they are heated electrically, they most often cost less than a buck a day. Some large tubs will go over that in real cold climates, esp. with heavy usage. Other, smaller tubs will easily be less than that.

At those prices, I would say invest in a better tub, and sit back, relax, and enjoy the fact that if it breaks, all you have to do is pick up the phone.

[Gary]

The R-value of the spa is irrelevant unless you have a good cover. Most forget that a spa cover is most of the heat loss from a spa when not in use. Get one with a 2lb cores and has an extra seal for the hinge.

Gary

[Chas]

Actually, the one-pounders have a better R value.

The two-pounders tend to be stronger, uh, and heavier.

Doc sells a cover that is up to 6" thick - I think he uses one-pound because with that kind of thickness the cover is plenty strong.