Questions about slab heat

[Big Chris]

So I bought a Super Wash site in April, and this is my first winter with it. Last night the temps fell to 18°F. I've got a question regarding my slab heat.

Please take a look at the diagram below.

Before I started messing with it, my attendant complained the floor heat never worked well, and he spent alot of time "chopping ice" last winter. When we tested it earlier this fall the natural gas boiler would run and cycle fine, but the pipe that ran to the floor heat manifold never really got warm. The mixing valve was wide open, but there was this sticker on the pipes next to the valve that reads " bypass valve 20% open". The sticker looks to be original. So I grabbed another ball valve I had laying around, and I "eyeballed" what 20% looked like (sighting down the bore of the valve) made a note of what the lever on the valve looked like and set the mixing valve to approximately this setting.

Wha-la, the pipe leading to the manifold instantly got warm, and I could eventually feel the return line from the floor no longer be "ice-cold". All was good with the world and after about 20 minutes or so I left for the night. This was on Monday. I should note that the pipe leading to the floor manifold doesn't get "hot" it gets warm......

Tuesday when I came in the circulator pump was running (indicating the slab thermostat was calling for heat) but the reservoir tank was ice cold, and the boiler wasn't on.... And the slab temp was approx 34°F. So I turned the system off and immediately back on and the boiler fired. So I sat and watched and waited and did some other chores. After 30 minutes of the boiler cycling (firing and shutting off), the boiler shut off and did not restart. Exactly 30 minutes. I retested. Same result at 30 minutes the boiler shut off even though the thermostat was calling for heat. That's strange, I thought.

During this time I made note that the boiler temp never got over 110°F (now that I changed the setting on the mixing valve). Then I had this eureka moment. The high limit was set to 180°F and the low was set to 140°F. Since the boiler never got to 140°F the system "timed out" and shut down after 30 min (this is my theory). So I set the low limit to 100°F. And now the system is working fine, and the floor heat worked flawlessly last night. Came in this morning (Wednesday) and the outside temp was 19°F and the floor is approx 38°F and everything seemed ok.

Sorry for the longwinded saga above but here's my question: Since the mixing valve was wide open and the fluid was just circulating through the boiler, the boiler was able to get to 140°F and not time out. Since I heeded the "bypass valve 20% open" sticker and then reset the low limit on the boiler my floor heat works. I can literally see stripes on the floor where the heat is melting ice, but is there something I am overlooking? Am I being inefficient? Am I way out in left field?

I am not a HVAC expert. I am not super familiar with these systems. Looking for advice here. Especially from another "Super Wash" site owner.

Thanks Chris

 

[soapy]

Your mixing valve is used so that cold water coming back from the slab does not hit the exchangers at such a cold temperature. It will shorten your boiler life if you hit the exchanger with cold water.

 

[Waxman]

I had a boiler issue this year with my Raypak ( for hot water production) not heating up the water very fast. The flue pipe would get warm, not hot.

The problem was a very dirty heat exchanger. Once the heat exchanger was thoroughly cleaned, the boiler worked perfectly and heated the water very quickly and the flue pipe got hot as it normally should.

 

[Overachiever]

Besides cleaning it like Waxman said, the only other thing I can remember about my old super wash boiler system is that there is a site glass on the reservoir tank and your fluids need to be in between the lines on it.

 

[Big Chris]

Your mixing valve is used so that cold water coming back from the slab does not hit the exchangers at such a cold temperature. It will shorten your boiler life if you hit the exchanger with cold water.

I bought myself one of those Harbor Freight infrared temp guns.....
I'll check out the "in" and "out" temps and report back.

 

[Big Chris]

Besides cleaning it like Waxman said, the only other thing I can remember about my old super wash boiler system is that there is a site glass on the reservoir tank and your fluids need to be in between the lines on it.

I had a pretty severe leak in the one manifold that I found and repaired during early season testing back in Oct. So super familiar with the lines on the reservoir tank as I was using them to determine if I had all the leaks repaired or not. Thanks for the heads up!

 

[2Biz]

The biggest thing people overlook with a "non Condensing" boiler, which I am assuming is what you have, is the boiler itself needs to run above 140° to keep from condensing. If run below 140°, the condesate that drips from the coils is extremely acidic and will damage the heat exchanger in a short amount of time. Thats why the newer High Efficiency "Condensing" boilers and wall demand heaters can run as low as 100° output temps. They are designed to handle the condesate using all stainless steel components and heat exchangers. The bypass valve you have is so you can make the boiler operate at 140° or higher. Hence the reason the low limit was set at 140°.

 

[GoBuckeyes]

We've run Raypack FH boilers since 1984 and unless my old memory is failing me, this is the first time I've ever heard of a "low limit" needing to be satisifed to continue to operate? My understanding is that there are two high limits....an automatic high limit and a secondary high limit that has to be manually reset (the one with a red button on it). I'd have to look at the settings as it's been years since I've changed any of them. I would also bet we've never run the floorheat with an output of 140F. The outgoing antifreeze is typically around 110-120f. The gas valves ought to have dials on them to set the modulation and help adjust the desired outgoing temp.

 

[2Biz]

I agree with your post about not running the floor heat "output" of 140°. But if you look at the diagram above, the way its plumbed allows for some of the boiler output to recirculate back into the boiler. There may be another bypass valve missing in the diagram that allows some of the return to mix with the glycol coming from the boiler. I really don't know how well these old systems worked when new? All I know is I tried using it when I first bought my CW and the first NG bill told me something was severely wrong!

The picture below was the 350k btu Jarco Webn boiler the CW had for floor heat. I Had no idea how to operate it and neither did the PO's! I quickly learned it had been allowed to run in a condensing state for too many years because they thought if they turned the temp down, it would be more efficient. When I took it out and salvaged the copper in it, there were no fins left on the coils....All eroded away from the condensate. So the efficiency was next to zero! The condensate also completely rusted away the metal frame it sat on...

To show the difference in how things were engineered then and now. The pump was 220v at 12amps! I am doing the same thing now with a Taco 013 120v at 2amps. And from 350k btu down to 199k btu and its able to keep bays ice free down to neg zero temps...Thats with 90° glycol going back out to the bays and demand heater set to 105° output.

 

[PaulLovesJamie]

Chris, nope you are not in left field. Nice thorough post/question, and nice job doing initial diagnostics, glad to hear you got it to work.
Also, all the answers/advice you got is good and accurate; yes setting that mixing valve is very important.
BUT...
The Lower Limit is set to protect the boiler and heating system. By lowering the LL to 100 you are bypassing part of the safety and operating parameters of the boiler, I would only do that as a very short term "fix".
So the question I'd be asking is why is the boiler not getting hot enough?
First thing I would do is what waxman said, open up the boiler and do an extremely thorough cleaning. Fingers crossed that it gets up to higher temps quicker after that and you can raise that LL. Consider doing it every year.
Then check to make sure you have a correctly sized and clean flue pipe, and make sure its drafting properly.
After that I'm not sure (I'm also NOT an hvac guy.)

Regarding your question about efficiency the short answer is YES, floor heat will cost you a ton of $, getting it to its most efficient condition is important! Understand, monitor, tweak and tune all of your boiler settings.

Im sure cash is a sore point since you just got into the car wash, but consider upgrading your boiler to a high efficiency unit, many of us (including me) have gotten excellent savings switching to an instantaneous unit for floor heat.

 

[GoBuckeyes]

Just stopped at one of our sites and took a look at a smaller Raypack 263k FH boiler. It only has one gas valve and the modulation numbers are way different than our larger boilers so you need the card for your particular gas valve. This is set at 2 which sets it 135F. The automatic high limit is set to 140 and the manual high limit is usually 10-15 degrees higher….so 150F.

Chris….if you have a Raypack and the only way to keep it running is to lower the automatic high limit setting something isn’t right as that’s not how it works. Most boilers don’t have a low limit, they have a flame sensor. If the flame sensor isn’t working it will shut down and lock out the system but that would be immediately after the main gas valve opens, not 30 minutes later. Again, if you’re running a Raypack the best thing you could do is call Huron Valley and speak to their tech support.

 

[2Biz]

All good information for the new owner! I know it can be over whelming at first, but if you'd like to learn more about floor heat and what alternatives there are to the old systems, you can do some reading on a thread I started over 11 years ago. It was me after my first winter!!! Dependiing on the size of your CW, you could get by with a single demand heater and pay for the installation in NG savings in just a few short years. My installation paid for itself in less than 1 year because of how bad my old system was! Pay particular close attention to post #126 in the thread below with statistics after the new demand heater was installed!

Date Range: Feb. 11th thru March 12th (2015) (29 days in Billing Cycle)

Temperatures:
21 days Max. temp was below 32°
29 days Min. temp was below 32°
19 days Min. Temp was below 15°
7 days Min. temp was below zero
Coldest night was -15°

NG usage in this billing cycle was 449ccf for a total of $440. The floor heat ran 100% of the time below 33°. I also added a 199K btu NG Water Heater that I didn’t have last winter. This usage includes the floor heat, 199K btu WH, 40K btu ceiling furnace, 2 burner wall heater that I run 1 burner below freezing and 2 burners below 15°…

(37) Tankless Water Heater For Floor Heat | Car Wash Forum

 

[mjwalsh]

2Biz .... That 135 post thread that you started & finished back in 2012 was a real EPIC imho. The fact that your system has stood the test of time is (11+ yrs) also to very much to your credit.

I notice with the Navien NFC-250/200H that we are currently putting in a residential retrofit in an existing with radiators (built in about a late 1950ish house) shows that from the boiler supply they want a check valve to avoid the possibility of reverse flow if the external pump quits running. I picked up the swing gate check valve from the wholesaler this morning to include in our gradual DIY install. I am aware that to get any of potential very lengthy warranty someone if not myself ... will have to defend every minutia of the install with the local wholesaler & the factory. https://www.navieninc.com/series/nfc-h

I do see eventual potential for cascading units at our laundromat, car n dog wash so hopefully we will not have any significant mistakes on "not as challenging of this specific install". A partial or complete "dry fire" would be the worst case ... usually ... because of a not thorough enough purging of the air in the system etc. The purging will be the most important process when we are at the end of the install. The Nibco-Webstone Pre-Piping manifold appears to be very helpful especially for installers on the amateur side of the trade! https://heatinghelp.com/systems-help-center/understanding-primary-secondary-pumping/

 

[2Biz]

2Biz .... That 135 post thread that you started & finished back in 2012 was a real EPIC imho. The fact that your system has stood the test of time is (11+ yrs) also to very much to your credit.

The purging will be the most important process when we are at the end of the install. The Nibco-Webstone Pre-Piping manifold appears to be very helpful especially for installers on the amateur side of the trade! https://heatinghelp.com/systems-help-center/understanding-primary-secondary-pumping/

I just started the floor heat this week. Flawless as usual! Its hard to believe its been 11 years already!! Pretty simple when you think about it and how it works!

As for purging...I put fill and test ports on both the primary and secondary plumbing lines. Makes it easier to use a sump pump in a 5 gallon bucket of glycol in order to pump out all the air in the zones and loop that goes to the heater. A second hose (attached to second fill/test port) goes in the bucket submerged in glycol so air connot be sucked back in the hose. Any air will be purged out of this hose...So yea, absolutely, you want to make sure you have ALL the air out before turning the heater on!

 

[Earl Weiss]

I just started the floor heat this week. Flawless as usual! Its hard to believe its been 11 years already!! Pretty simple when you think about it and how it works!

As for purging...I put fill and test ports on both the primary and secondary plumbing lines. Makes it easier to use a sump pump in a 5 gallon bucket of glycol in order to pump out all the air in the zones and loop that goes to the heater. A second hose (attached to second fill/test port) goes in the bucket submerged in glycol so air connot be sucked back in the hose. Any air will be purged out of this hose...So yea, absolutely, you want to make sure you have ALL the air out before turning the heater on!

3 Pumps? 2 in line? Reason?

 

[GoBuckeyes]

2Biz, when you re-did your FH how did you flush all the sludge out of the old system? The glycol in my floor heat systems looks very dirty. I can’t imagine that little filter screen on the HE boiler not plugging constantly.

 

[2Biz]

3 Pumps? 2 in line? Reason?

The 2 pumps inline was required to give the demand heater the right pressure. I origianly installed (1) based on Takagi support recommendation! Boy was they wrong! I was only getting 3gpm through the heater at 20psi...Adding a second pump inline doubles pressure. So now I get 6gpm with the 2 pumps inline, which is enough to get the most out of the heater I have. Adding pumps in parallel keeps pressure the same and increases volume by the amount of pumps you have. Even though my heater is rated at 10gpm, it takes 100psi to get it there! Then temperature differential affects throughput too....All things you need to know from the manual (flow charts) when designing your system.

 

[2Biz]

2Biz, when you re-did your FH how did you flush all the sludge out of the old system? The glycol in my floor heat systems looks very dirty. I can’t imagine that little filter screen on the HE boiler not plugging constantly.

Good question! I used a 5 gallon bucket and a cheap garden hose sump pump and put a 5 micron filter inline. Let that run for a few days. Then when I filled the system, I used the same sump pump to fill the system, but took out the filter, didn't think I needed it! Mistake, you are right, it plugged the small filter in the heater in just a few days. So I had to use the bucket and sump pump again along with the filter and ran it that way for a few days. Without the heater running of course. I haven't had to do that again for 11 years now! Most of these heaters have the flow rate displayed on the main screen. Mine hasn't changed since I got it all filtered out. 6gpm with the two Taco 013 pumps....

 

[2Biz]

Btw, I just used clothes washer water hoses (female both ends) for the fill and air purging of the system...

 

[mjwalsh]

I just started the floor heat this week. Flawless as usual! Its hard to believe its been 11 years already!! Pretty simple when you think about it and how it works!

As for purging...I put fill and test ports on both the primary and secondary plumbing lines. Makes it easier to use a sump pump in a 5 gallon bucket of glycol in order to pump out all the air in the zones and loop that goes to the heater. A second hose (attached to second fill/test port) goes in the bucket submerged in glycol so air connot be sucked back in the hose. Any air will be purged out of this hose...So yea, absolutely, you want to make sure you have ALL the air out before turning the heater on!

Earned kudos for 2Biz,

I see by your photo that you did adhere to the 6 inch primary-secondary rule! I found an extra good visual simulation explanation on YouTube about the potential complication that some can avoid by paying attention to that 6 inch rule:

(1) Primary-Secondary Pumping on a One-Pipe Hot Water Heating System - YouTube

It definitely relates to some of your mentioned needed gpm realities!