Floor Heat Thermostat Temp Settings

[MDrost1]

Folks,

Up until last year, I had a boiler that was severely undersized for my floor heat. I installed a Raypak this year and it seems to be a lot more efficient. I have four questions about operation.

Preface:
My slab thermostat is set to come on at about +/- 38 degrees and maintain the floor heat around the same temp(as I understand it). It is an original T-stat from 1987. Down to about 23 degreesish I have good ice melting. Anything lower is iced over.

Question: If I increase my temp on the T-stat, will that give me better ice melting? (I know stupid question)

Question 2: Will raising the T-stat "on" temp have any adverse effect on the concrete it heats?

Question 3: For you folks who live in the Midwest(I live in west Michigan on the lake), with crazy changes in weather and temps, where do you have your floor heat "on" temp set?

Question 4: What kind of ice melt should I expect at very low temps 0-20 degrees?

THANKS!

 

[slash007]

I have mine set at around 34. 38 is probably too high. You do want the concrete warm though before ice hits or it will just build up. To be able to stay ice free at lower temps, you would need to higher the temp on your boiler. I know 2biz stays ice free to below 0, mine is usually ice free until about 10 degrees or so at one wash. At my other wash the floor heat is a joke and ices up easily.

 

[MDrost1]

So where the slab temp is set, says about 38 on the thermostat. Slab temp, not ambient. I am not sure how accurate this is because the thermostat is a 30 year old analog type(Honeywell). I get ice at 15 degrees for sure. Always have ice at 0.

The installer said to raise the temp 4-5 degrees and see how that works. By all accounts, they say that raising the temp won't damage the concrete. Correct?

Does it sound like I am on the right track?

 

[I.B. Washincars]

I don't see how raising the turn-on temp will help. IMO, you need hotter fluid running through the floor. If you can increase the boiler temp without tripping high limits I would try that. Closing the bypass some may help as well. Before you go changing settings record the current position as a baseline so you can go back to that when things don't work out the way you hoped they would.

 

[MDrost1]

My boiler is at the max temp for production. I had my installer in, and he said to increase the slab temp at the thermostat. We will see. I am excited to actually see floors without ice.

 

[Eric H]

My boiler is at the max temp for production. I had my installer in, and he said to increase the slab temp at the thermostat. We will see. I am excited to actually see floors without ice.

Increasing the slab stat will help but i'd recommend making some changes on the controls for this boiler. You stated that this is a new Raypak boiler, can you get a model number so that we can look up an installation manual? I also need the BTU size and the square footage of the area that you are trying to heat, this should include any heated aprons but not the equipment room.

Also, I recommend getting a n infrared thermometer https://www.amazon.com/Tektronic-IT...9824&sr=8-46&keywords=non-contact+thermometer this will help you adjust the floor heat temp properly instead of trusting the dial on the t-stat. You can probably get one at Harbor Freight if you have on close by.

 

[2Biz]

+1 on what Eric said. You need an infrared gun to check the slab surface temp of each of your bays, get an average, and adjust t-stat setting accordingly. Without knowing your setup, its hard to give recommendations on how to adjust your t-stat. There are many variations on how systems are installed and some don't work well no matter how well you try to fine tune. IMO, I don't know how a single slab stat can accurately control the system to keep all bays ice free. Heat load can vary between the bays throughout the day/night.

Back when I designed/installed my system, I did lots of research. From the research, I learned the best system to install was a primary/secondary system where the main floor loop (Primary) circulates 100% of the time below 32°. The boiler (Secondary Loop) is fired from an aquastat located on the return line from the bays giving an average of all bay return temps. In my case with a 4 bay, and with a 15° differential aquastat, the boiler fires at 55° return temp and shuts off at 70°. The boiler is set to 105° and pumps 105° coolant into the main floor loop. It mixes with coolant that is coming back from the bays and roughly 80-95° glycol goes back out to heat the bays. When the system energizes at 32°, with the 15° differential, the boiler cycles on and off every 15 minutes. 15 minutes on 15 minutes off. The colder it gets the longer the boiler stays on and the off cycles are shorter, but the complete cycle is always 30 minutes long. It took a little trial and error and the infrared gun to find the optimum setting on the aquastat, but once I found the magic number, I haven't touched the aquastat and boiler temp setting since I installed it...

This system (199K btu Demand Heater) has been tested to -16° and keeps all my bays ice free. The boiler still cycles on and off at these temps. Last week it got to -10° here. I do not have bay doors and one of my bays is outside with no roof. There were folks washing all the way down to -5°....Floors remained ice free but the walls had over an inch of ice on them! I timed it just right when it warmed up to get the ice off the walls, but doable!

I guess I'm going over this again to share what I learned and attest at how well it works. If you want a trouble free, self regulating system, you might want to consider making some changes. Here are a few pics to ponder over...

 

[Jeff_L]

FWIW - I haven’t used a slab t-stat in years. I simply measure the return temp of the glycol and cycle the boiler from that. Measuring one part of a slab that’s huge doesn’t make sense to me. Maybe I spend more money this way, but I have no ice on in the bays.

 

[soapy]

How much area are you trying to heat? What size is
Your boiler? In my area it takes 400,000 BTU boiler to keep a 4 bay SS with heated aprons Ice free. Any smaller and I get ice around the edges starting at 15 degrees. You will find a wide variety of temps in your concrete. Where the slab sensor is May be different from other areas. I find a temp for the sensor area that works to keep rest of the floor clear and leave it there.

 

[2Biz]

Sizing the boiler also depends on whether it's an HE condensing design too....It all plays a part...

 

[Rudy]

Raising your set point on your thermostat (in an effort to keep your floor ice free at lower temperatures) is like trying to heat your house with a small space heater. Yes, raising the space heater's set point to 85F will preheat the house to a higher temperature...and will, to some degree, TEMPORARILY keep the house warmer when it gets cold. But....it won't last. What is needed is a properly sized (ie furnace) which can keep up with demand. How efficient is it trying to heat your house with an undersized heater? It's not. It's horribly inefficient.

Years ago, I moved from a slab stat system.....to a return line sensing system. At my wash, a 75F return line temperature keeps the slabs just above freezing.

Also...

There's a modulating valve on my ancient RayPak boiler. This sets the amount of gas sent to the boiler. This allows you to dial (up and down) the BTU output of the boiler. It's more efficient to have the unit fire for a protracted period....than to have it start and stop repeatedly.

Perhaps your mod valve has been set too low. Check. You need enough BTU's going to the floors without having to "cheat" with higher set points.

Your wallet will thank you.

 

[MDrost1]

So,

My boiler was sized properly for about 4500 sq ft. of floor heat. I am recalling this off the top of my head. Maybe 627,000btu? Don't quote me on that. The previous boiler was severely undersized. It ran all the time will little ice management.

My new boiler was installed in September. The slab t-stat is the same one used on the former unit. Set at the same temp. from last year.

The modulating valveon my new boiler is set to 10. The highest setting.

I received my gas bill for December. It was about 1/2 of the cost it normally is. I figure the new boiler is more efficient and therefore, I could push my threshold a bit. The installer agreed.

My HVAC installer came out and suggested turning the slab-stat up 5 degrees. We have had 15 +/- for the past four days. No ice. A minor miracle. Previously, the ice spud would be out, cracking and spraying ice. Before it would not melt snow...2-4 inches. We have had about 4 in the last 24 hours. No snow in the bays.

I bought and temp gauge to measure the floor temp. I am going to start more active measurements. Thanks for the tip!

I understand the return line sensing. That makes total sense to me. I am going to look into that! Thanks for all of the advice. You are all great!

 

[Eric H]

The modulating valve on my new boiler is set to 10. The highest setting.

I think this may be your problem, but not entirely sure. Setting 10 is 170 degrees according to my manual. I think the boiler may be short cycling or modulating the temperature down because the "bypass loop" (where the ball valve connects your supply and return lines) is getting the boiler to temp very quickly but the supply lines out to the bays are at a much lower temperature.
Try going to setting 4 with the ball valve on the bypass at about halfway open. How open/closed is the ball valve now?

 

[wash4me]

You can google how to determine your btu's being consumed by counting the turns on the gas meter and then you would see if it's really running at capacity. Unbelievable how non technical the average hvac installer is.

 

[MDrost1]

Eric H,

So my production temp doesn’t get above 100 degrees when I point the infrared temp gauge at the “holding tank”. Could it be the modulator and gas setting? Wondering if you can offer some more instruction.

 

[Eric H]

Eric H,

So my production temp doesn’t get above 100 degrees when I point the infrared temp gauge at the “holding tank”. Could it be the modulator and gas setting? Wondering if you can offer some more instruction.

You should be getting temps well over 100 degrees.
did you adjust the bypass valve between the supply and return pipes? should be closed at least half way.

can you post a picture of your set up with the front cover off of the boiler as well as the piping to the sight tank and pump?

 

[MDrost1]

Apparently I have a Hi Temp modulator. Starts at about 170. My bypass was cracked open about 1/4 of a turn. I opened the valve about 3/4 of a turn. I turned the modulator down to LO per Huron valleys rec. I’ll try to get pics soon. It is a 627,000 btu hydronic atmospheric boiler from Raypak.

 

[getnbusy]

THis is a great discussion about floor heat.

I have a nice raypak for a deal if anybody wants to make an offer. we don't need floor heat here

pm me if interested