gas heater limitation usage for spa during winter termpertures ?

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tstex

Silver Supporter
Aug 28, 2012
2,186
Houston, TX
Hello to All,

I have read [somewhere] that using the natural gas heater during winter temp's is ok as long as the temp's do not go below XX? The questions I have stem from not only the air temp, but water temp, and some common sense operating instructions.

Read my manual, but it did not state anything other than do not operate during "freeze-mode" like temp's or below. The main objective I am trying to achieve are operating conditions and operating procedures that do not: crack the heat exchangers or damage the system. I always do a spa FC & pH test before operating.

So, what pool temperatures, either water or air bring potential damage if operated?

Once I have the spa/heater operating, my max temp setting is 100. I sometimes turnoff the heater [from my remote] btw 95-99 if I feel it's warm enough. Also, when I am done w the Spa, I always run the SPA/Pump w heater in off position for 10-15 minutes at a min. Once done, I'll change from SPA to POOL mode and run FILTER PUMP at a very low speed from the spa spillover to allow for a slow water temp equalization.

Thanks for your feedback, and I hope all the TFP owners that have experienced freezing temp's, that you experience little to no problems at all.

Regards, tstex
 
I believe the main issue is that when you operate a heater with water temps below 68F, condensation can form in the heat exchanger causing corrosion. But because the spa water heats up so quickly, I don't believe this is much of an issue. It is more of an issue with heating pools with cold water temps since the water temp will stay lower for much longer.
 
Thanks Mark...I've heated my spa when the water was in the low 50's and it's taken over an hour to get to 95...Heck, when the water is above 68 in Houston, that's almost like spa temperature anyway...I'm hoping w a 400,000BTU gas heater, and the gas meter pumping in some pretty healthy volumes of gas, that the heat from the unit will almost certainly evaporate any condensation that forms...

I sure hope what your saying is not the case...I really like the spa when the temp outside is 50 degrees or lower...nothing like some steam coming off the spa - tstex
 
tstex said:
I'm hoping w a 400,000BTU gas heater, and the gas meter pumping in some pretty healthy volumes of gas, that the heat from the unit will almost certainly evaporate any condensation that forms...
Click to expand...

Don't count on it. You will still have some condensation but not as much because the water would heat faster.
 
Mark & Paul,

Is there a 100% safe way to fire-up the gas heater and visually see the condensation process? I am not familiar w the internal parts and design of the heater to first know can you even observe where the condensation takes place, and if so, can it visually be seen? I would assume the main cover has to come off and if so, is there a safety lockout or similar that if the cover is off, it will not even fire-up?

Point being, I am not doubting you, but if I could determine the amt of condensation under X variables, then I could possibly ascertain the type risks of damage if used w X variables.

I sure am disappointed in the temperature issue bc my favorite time to use the spa is when it is much cooler outside. However, knowing I am potentially damaging the heater sure doesn't settle well either....thanks again, tstex
 
I'm with you tstex. We also like to use the spa in the winter when it is cold outside; we heat up from water that starts in the high 40s or low 50s. We do this about once per week and it probably takes about 20-30 minutes to pass 68 degrees, where it sounds like the condensation issue drops off.

I wonder if a cupro-nickel heater would be a good deterrent against the condensation/corrosion issue?
Also wondering if the corrosion possibility is compounded by higher-salt content water.
 
Not sure which model Hayward you have but usually you can hear a sizzle sound which is the condensation coming off of the heat exchanger and dripping onto the burners. If you have the FD model of Hayward, it would be harder to hear this based upon the construction of the unit. The older ED2 style units, you can hear the sizzle sound when it happens. Adding an external bypass can lesson condensation as you are bypassing some of the cold water from the heater so the water that does transfer thru the heat exchanger has a better chance of heating without condensation happening. However, it will take a bit longer to heat the water at times because you are sending unheated water back to the location.

Manufacturers say prolonged operation with water temperatures below 50°F is not recommended. When starting the heater with water temperatures below 50°F, operate the heater continuously until higher temperatures are reached. Operating the heater for prolonged periods with pool water below 50°F can seriously damage the heater, and is not covered by the warranty. I always suggest that homeowners heat their spa over the pool when water temps are cold. Seeing that is what you are doing, you should be OK but you can take actions to lesson some of the condensation issues by adding that manual bypass outside of the heater.

Most people do like to use their spa when it's cold out.
 
Dodger said:
Also wondering if the corrosion possibility is compounded by higher-salt content water.
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The corrosion from condensation is on the firebox side of the heat exchanger (i.e. external). The cold water inside the heat exchanger pipes causes condensation on the outside of the heat exchanger pipes. But because it is burning NG, it also is very acidic water. It is really a matter of duration of the acid water on the exchanger as to how much damage is done. A pool heat up takes 10-20x longer to get to 68F based upon volume difference so a pool heat up is worth 10-20 spa heat ups in terms of damage.
 
Thanks guys....few clarifications and questions:

1. Paul, thanks for the question on heater model..it's a Hayward H400FD. I'm going to update my signature today to make note of the model - thanks Also, if I can work w 50 degree + temps, then I'm ok with that...I never heat the pool, but my spa is 9'x9' so there's some serious vol there.

2. Our pool is CL, not salt based. Regarding the acid content, I was informed or told on the forum to add a little M-acid to the spa right before it's heating up to prevent post scaling..well, I would rather have a little scale I could remove from the tile water line than an issue w having to replace the heat exchanger. So, I'll guess I'll be skipping the MA add while heating the spa.

3. Dodger, how old is your heater? if you guys are heating 1 time per week at 45-50 degree temps during winter, you should be able to examine your heat exchanger and discern of there's any issues.

As mentioned, I will not spend time heating the pool, only the spa and will never try heating the water at anything below 50 degrees...but like dodger said, getting into a hot spa while it's cold outside is why I bought the whole system. Our pool/spa water temps went down to 44 degrees while we had no sun and low 20's during the recent cold spell. But it's already back up to 54 degrees.

Last thing. Since I have the Hayward H400FD series heater, can someone inform me if there's a safe way [w out taking anything apart that is critical] to view the outside heat exchanger pipes or other to ascertain if there's any bad etching or corrosion? Anything I should specifically be looking for if I can indeed take off cover and view the heat exchanger. I will, of course, turn off the heater at the breaker panel. Anything else as a precautionary measure(s)? I'll also turn off the gas-line that feeds the heater as well.

Thanks, tstex
 
tstex said:
3. Dodger, how old is your heater? if you guys are heating 1 time per week at 45-50 degree temps during winter, you should be able to examine your heat exchanger and discern of there's any issues.
Click to expand...

Our heater is 18 months young (July 2016). I don't know how/where to examine the heat exchanger, but will follow their advice to you, given that my heater is a different make and model. Basic self-inspection is a good idea as long as we can do it safely.

The previous heater here was a 25-30 year old Raypak. That Raypak was on its last legs when we moved here 3 yrs ago, but I could coax it to work if I cleaned the filter, with the idea of maximizing water pressure in there. I have to imagine that multiple previous owners used the spa in the winter, so the condensation was happening and it still lasted over 25 years.
 

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Dodger said:
Our heater is 18 months young (July 2016). I don't know how/where to examine the heat exchanger, but will follow their advice to you, given that my heater is a different make and model. Basic self-inspection is a good idea as long as we can do it safely.

The previous heater here was a 25-30 year old Raypak. That Raypak was on its last legs when we moved here 3 yrs ago, but I could coax it to work if I cleaned the filter, with the idea of maximizing water pressure in there. I have to imagine that multiple previous owners used the spa in the winter, so the condensation was happening and it still lasted over 25 years.
Click to expand...

Wow, 25 yr old heater. I would suspect the material, thickness and quality of the heaters made 25 yrs ago are a bit better than all the throw away equipment they make today.

I would suspect that all or most of the models are the same, w the exception of a diff label slapped on the front. good luck w your heater..tstex
 
mas985 said:
The corrosion from condensation is on the firebox side of the heat exchanger (i.e. external). The cold water inside the heat exchanger pipes causes condensation on the outside of the heat exchanger pipes. But because it is burning NG, it also is very acidic water. It is really a matter of duration of the acid water on the exchanger as to how much damage is done. A pool heat up takes 10-20x longer to get to 68F based upon volume difference so a pool heat up is worth 10-20 spa heat ups in terms of damage.
Click to expand...

Can you clarify about the acidic water? I took this to mean the condensation water on the outside of the heat exchanger becomes more acidic because of burning NG. If yes, then it would be good to hear about the mechanism a little. Or did I misunderstand?

tstex said:
2. Our pool is CL, not salt based. Regarding the acid content, I was informed or told on the forum to add a little M-acid to the spa right before it's heating up to prevent post scaling..well, I would rather have a little scale I could remove from the tile water line than an issue w having to replace the heat exchanger. So, I'll guess I'll be skipping the MA add while heating the spa.
Click to expand...

Or is this the correct approach? I've been adding MA to drop my pH from ~7.8 to 7.5 as I heat up my spa, in order to manage scale. Is this pH adjustment bad for the heat exchanger?
 
It is much more involved to check the internals of a Hayward FD unit vs. the older models. You literally have to dismantle the unit to check it along with looking at the burners. It's a big pain in the behind.

I would say as long as you only heat the spa, I wouldn't worry too much. I would be more worried that the heater will leak at some point like almost all of the the other Hayward FD units do. I just removed one last week, under 3yrs old. Leaking heat exchanger in the back corner of the left side. The same spot they all seem to leak.
 
ps0303 said:
I just removed one last week, under 3yrs old. Leaking heat exchanger in the back corner of the left side. The same spot they all seem to leak.
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Can you tell if the corrosion was from the inside (poor water quality) or outside (condensation) of the heat exchanger? Or did the leak have nothing to do with corrosion?
 
mas985 said:
Can you tell if the corrosion was from the inside (poor water quality) or outside (condensation) of the heat exchanger? Or did the leak have nothing to do with corrosion?
Click to expand...

Thanks Paul for your post and Mark, those are great questions...

Paul, can you provide a reference point on where to look for the "heat exchanger in the back corner of the left side. The same spot they all seem to leak". Also, do you have any clear instructions or a process for accessing the heat exchanger re the back corner? If I am looking at the unit from the front w the LED pad on the right top front, that's the right front corner. Is the leaking at the bottom, middle or top area, or some hybrid thereof, of the back left corner? Is there any specific reason why it's always in this place ?

Thank you very much, tstex
 
Tstx, re
Last thing. Since I have the Hayward H400FD series heater, can someone inform me if there's a safe way [w out taking anything apart that is critical] to view the outside heat exchanger pipes or other to ascertain if there's any bad etching or corrosion?
Click to expand...

I don't have your type of heater so this may not be true in your case but without taking the heater assembly apart and removing the heat exchanger, your options are a mirror or an endoscope camera.

With the heater off, place a mirror into the area, above the burner if possible, or below up through burner rods. Likewise for an endoscope.

What you're looking for in terms of identifying a combustion/condensate problem is:
A) evidence of sooting (black) and, or, if viewable, b) condensate itself, which tends to be a darker green, sticky substance

If with your type of heater you are able to view the burner while its burning, also look for a good blue field of flame with only a bit of orange. It there's lots of orange and particularly yellow flame, plus any sizzling as others mentioned, that's a sign of improper combustion which causes the condensate -- or the condensate causing improper combustion.

By way of background, I am in the most of trying to work out exactly what caused the premature failure of my cupronickel exchanger after 18 months...with sooting and condensate rapidly developing in its last 2 mos. of life. In my case, which is not necessarily germane to your situation, I am using my heater in a heated pool house in very cold winter temps but with water that never drops below 88 degrees (because we heat it daily and operate in a dome.) We currently suspect that a tech's removal of the top shield caused venting issues that led to improper ventilation and resulting condensate, since that accords with the degradation timing. But we may also come to find that we have flue temp issues that exacerbated the failure. We've sent off some info/pics for initial analysis and may have more info in coming weeks.

In your situation given the ad hoc nature of spa heating, I'd suspect you could go much longer without any significant degradation issues, but periodically inspecting via mirror or camera the underside of the heat exchanger would help avoid problems.

Sooting, for example, will rapidly increase the corrosion problem, but can be ameliorated by dissembling the heater and cleaning the soot off the underside of the exchanger. Hope that helps ;)

Paul will have real world experience with your model, so ignore my tips if he suggests otherwise ;)
 
Thanks a million swampwoman...that was an extensive follow-up.

When the water temps get a little warmer [went from 45 to 54 and now back to 50, & going to be 27 air temp this weekend], I'll fire-up the heater and determine if I hear any sizzling at the initial start-up and for the first 1-10 min's. I can tell you that there is a large hummmming sound from all the gas burning, so if the sizzling is barely audible, I might not detect it, if it exists.

I am a firm believer in the policy: "if you do not use it, you will lose it". We didn't ignite our fire-bowls for 4-6 months and now they are toast...need to troubleshoot those things soon. I, at least once per week, fire-up the heater to get her going, keep the orifices clean of spider webs and anything else that takes a few weeks to build or embed themselves in there.

Good luck w your results and post back what you find...any pics would be great...and yes, anytime you lose your good blue flame to orange of yellow, there's a mixture ratio issue and something is not right...I like gas grills, but I've never had a flame issue w my huge BBQ pit: brisket, turkeys, hog shoulders, burgers, ckn, shrimp, the flames are always just right and I've never worried about what drops or how long on the flames :party:
 
tstex said:
Thanks Paul for your post and Mark, those are great questions...

Paul, can you provide a reference point on where to look for the "heat exchanger in the back corner of the left side. The same spot they all seem to leak". Also, do you have any clear instructions or a process for accessing the heat exchanger re the back corner? If I am looking at the unit from the front w the LED pad on the right top front, that's the right front corner. Is the leaking at the bottom, middle or top area, or some hybrid thereof, of the back left corner? Is there any specific reason why it's always in this place ?

Thank you very much, tstex
Click to expand...

I'll post some pictures later that shows the spot where they leak. It's very consistent from Hayward FD heater to heater and doesn't matter the size, 250 vs 400.

I see way too many of these Hayward's leak to say it's a chemical issue. Especially when they all leak in the same exact spot.
 
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