My wife and I build a new pool this year, with spa. (My last house had a pool with no spa, so the spa part is pretty new to me).

Anyway, it was great in the summer, turn it on, it heats up - great. But now that winter is arriving, I'm having trouble getting it hot enough. I have the thermostat set to 103, but once daytime temps starting dropping to the 70s, my spa would only heat up to 99 or so (on colder days only 95).

Well last night when the temperatures dipped down below 50, I wanted to heat up the spa and it only got up to about 92.

My question is: Is this 'normal' behavior? or should I expect to get that thing up to 104 in the dead of winter? (I mean, it's reasonable to me that it has a harder time heating when it gets cold out, but I want to know if everyone lives with this, or does it mean my heater is undersized?)

Equipment wise: My heater is a Pentair 400k btu unit, and I don't know the exact size of my spa. It holds 8 comfortably. It has a lot more surface area though because it spills over on all 4 sides (or it does when the pool is running. No spill over when heating the spa obviously).

Thanks.

Does it have a spa cover? If not then the behavior it is showing seems normal. Are you able to draw and return to the spa only from the heater? A pool cover makes a big difference when the temps drop below 60.

Some info: http://www.energysavers.gov/your_home/w ... opic=13140

I heated mine from 60 to 102 in 30 minutes. 400k heater. Maybe you need bigger meter?

Wow, mine wouldn't heat that quickly either! I emailed the builder, and he actually stopped by and said the regulator was at a lower pressure than it should have been (moved it from 4.9" to 7" of water column). Hopefully that helps with the speed and the peak temp.

Attaching a pic below. My spa is a bit bigger (but also has that increased surface area which makes it *look* even bigger, but I think that surface area is all giving up heat). Anyway, we'll see if the increased gas pressure helps.

I can heat my spa in less then 30 minutes to 100 when it is at 60 degrees water temp. We live in Richmond, Tx so we are in the same general area. Nice pool/backyard BTW.

Is there automation running the system or are you just relying on the heater logic/temp controls?

I am very curious to hear your results. I have a large spa as well... I was hoping I would not have to go tandem heaters.

Make sure to turn the air supply off while preheating the spa. That cuts that time to heat it by about half in colder weather. Blowing cold air through the water you are trying to heat is counter productive. I can bring my 7x7 square spa from 60 to 100 in about 35 min.

I have a 600 gallon spa and I can heat mine from 70 to 102 easily within 30 minutes or less. I've got a 400K Pentair heater. In comparison, if you're not getting equivalent to that, something isn't working. I do have a spa cover (3" thick) on it full-time which not only retains the heat all the time, but also during the heating process which certainly quickens the heat-up time.

Can you get custom spa covers. Not round or square.

Had larger gas meter installed yesterday so I will fire it up for the second time later this week and compare.

How much does it cost to heat it? I forgot to take gas electric readings prior.

Ok. So problem solved. It's important to note that when it was only heating to 95, I was getting in and saying, "I know it's only 95, but it feels good. Must be because it's cooler out". And when it only heated to 92, I didn't get in because I was just trying to see if it would heat that night.

Anyway, heated it up tonight, it only showed 92 on the handheld (spishex - yes, there is an automation system running it). I walked outside with my IR Thermometer and the pool read 103. doh! Then I ran back to the heater itself which read 103.

My two major mistakes:
a) Assuming that the temp sensor on the pipe to be accurate.
b) Assuming that the thermostat logic was governed by the temp sensor on the pipe, and not the heater itself (in which case I would have expected it to heat beyond 92, and the fact that it wouldn't would have been because the heater wasn't up to it)

In my defense, it was weird the way that temp sensor was failing. Basically, it read low, but as the outdoor temperatures dropped, it's error increased. This led to a correlation between the 'reported max' temp I was reaching and the outside temp causing me to think the heater didn't have enough power to heat the spa.

My spa does still seem to take longer to heat, but that's almost certainly a function of all of that surface area. I can see the steam lifting off of it like crazy. (Since it runs over on all sides, a cover is probably not practical).

Emailed the pool builder and he's sending someone out to replace that sensor today. (I can't say enough about my builder. I know there's a lot of crappy builders out there, but my guy isn't one of them. Not sure what the rules here are about publishing a recommendation, but if anyone wants a good builder in Houston, PM me and I'll send you their name. He wasn't cheap, but he includes a lot of extras, so the premium isn't actually that much. Everyone LOVES the pool and his main concern at all times seems to be that I'm satisfied. I found him via a neighbors recommendation, and the after sales support for both of us has been top-shelf).

TL/DR: My bad - sensor broken.

Good to read problem solved. You have a really nice setup. I see how a cover wouldn't work in you case. What does it look like at night with the fires going?

Thanks. Here's a shot from the same IP Cam...