Floor Heat Temp. Settings

[Andyjmyr]

What is everyone's protocol on how they set their floor heat temp? The utility company here is raising the price on Natural gas...again. I'd like to see the different ways operators go about setting the temp on the floor heat.

Do you look at the weather? If so, do you look at tabular forecasts?

Thanks!

-Andrew

 

[MEP001]

We don't have or need floor heat in this area, but I read a lot that operators use the return line temp to control the heat. It makes sense to not have the water returning at 70 or 80 degrees because that means unnecessary heating of the slab - keeping it above 32 is all that's needed to keep it free of ice. Others close bays in the coldest weather and put down insulating blankets or have doors on the bays to keep from losing too much heat.

 

[Waxman]

My distributor wisely had me put insulated doors on all my bays. Last winter I left them open 24/7. Not this winter! I hired a local guy to come by at night and lower the SS doors (IBA has automatic doors). Now I come in to bays that are above freezing. I also use far less propane! It isn't worth a tiny bit of business to keep the doors up and heat the slab all night with the wind howling thru the bays. Plenty of time for people to wash besides midnight in the freezing cold!

ps; i use a slabstat and set it at 46. pretty much covers me.

 

[Bubbles Galore]

The way I have mine setup is to cycle when it is below freezing to keep the slab, ice free. Between 12-6 a.m. if the temp. is above 20 degrees then the boiler shuts down. If it is below the setpoint, then it goes on a restricted cycle during that period.

 

[Eric H]

Floor heat return temp cut-off

A couple of years ago I tried to use the return temp on the floor heat to turn the boilers burner on/off as suggested by others here. I could get the boiler to turn off, but it would not come back on. I finally hooked it back up the original way and never got back to it. Friday I was waiting for an appointment to show up and I started looking at the boiler again and got out the wiring schematic. Looks like I'm supposed to hook up the t-stat inline with the flow switch. Is this the way it is supposed to be done?

 

[MEP001]

Boilers can be different. Some have the flow switch act as a safety for the boiler, others will actually use the flow switch to turn the boiler on/off and only the motor is controlled by the thermostat. There are a lot of possibilities from a mistake in wiring to a bad flow switch to a system problem. I've seen someone add a timer to his boiler to turn it off at night, but he put the timer on the main power instead of wiring it into the system. Laars boilers need the pump to run for a couple minutes to leech the heat from the exchangers, and when the timer would kill the power with the boiler running it would trip the manual-reset high limit and not come back on the next day.

 

[Eric H]

When I push down the test switch for the flow switch the circ pump stays on and the flame cuts out. There is a air stat option on the wiring schematic in line with the flow switch. I just wanted to check to see if this is the way others have/ are doing it. BTW: it is a Raypak boiler.

 

[dreese]

A common way to wire a Raypak boiler uses 2 thermostats and a flow switch for burner control. Most RayPaks have operating and hi limit thermostats built in.

An air or slab stat wired to make on drop is used to start the system circulating pump at the desired temp - usually 32-34 degrees. A flow switch is used on the outlet side of the boiler and is wired in series with an aquastat located on the return side of the system (before the boiler). This aquastat (either a strap on attached directly to the return plumbing or located in a well) is wired to break on rise.

When the air or slab stat makes, the circ pump starts and makes the flow switch. Since the return fluid temp is below the aquastat set temp, the burner fires. When the return fluid reaches the aquastat set point, the aquastat breaks the circuit and the burner stops. The pump continues to run so the flow switch is still made.

Most aquastats allow a 5 - 7 degree drop before remaking (this is adjustable). When the aquastat remakes the circuit, the burner fires again and the cycle starts again.

 

[MEP001]

Thanks, I know boilers pretty well, but not floor heat systems.

 

[Earl Weiss]

We don't have or need floor heat in this area, but I read a lot that operators use the return line temp to control the heat. It makes sense to not have the water returning at 70 or 80 degrees because that means unnecessary heating of the slab - keeping it above 32 is all that's needed to keep it free of ice. Others close bays in the coldest weather and put down insulating blankets or have doors on the bays to keep from losing too much heat.

Maybe yes and maybe no. Checked my floor heat yesterday. Boiler set at 120 degrees. By your rational this would be excessive, but keep in mind the furthest it goes out is 6 bays away (maybe 75 to 90 feet). So, you have heat loss over that distance to the bay, heat loss as the tubing travels under the floor, as well as the heat loss from the tubing is to the surface.

So, I would think you would need to start at a temp where the return line was at least 32 degrees, and factor some addittional amount for the loss from the tubing to the floor surface, and set the supply to provide the neccessary temp for this result. However if you have the return at only 40 degrees, it may be too difficult for the Boiler to raise the temp to a point where it will be at that level in the short time it takes to pass thru the boiler.

For instance the other day it was 15 degrees out. If the boiler can give you a 60 degree rise in temp, and the liquid will drop 60 degree as it travels, having the supply set at 90 degrees won't work.

 

[Rudy]

Finding the correct return line temperature starts out as somewhat of a guessing game. I read on this forum to start at 75 degrees....and that turned out to be darn close.

When we set the return temperature to 75, the slab is just barely above freezing...just barely. When it gets extra windy, or extremely cold, we have to raise it a degree or two.

Don't forget, you aren't actually heating the slab to 75 degrees anymore than you are heating it to the output temp of 120 or whatever. What you ARE doing is transferring heat.

If the slab is just barely below freezing, it will not take very much time for the 120 degree hot water to heat the return line to 75 degrees. When it does, the boiler ceases firing, and the slab is just barely ABOVE freezing.

Make sense?

 

[Eric H]

i spent some time on this project today. The reason that I could not get the return temp t-stat to work properly was that I copied the wiring from the slab stat. Whomever wired it originally set it up to make on rise, not to break on rise. I wonder how much gas I wasted these past 4 years having it wired wrong. It isn't the first thing I've found that was not wired correctly.

 

[Bud]

I have 2 boilers with slab stats and 1 in an IBA with air/return liquid stat. I really prefer the slab stats but they both work fine. Over the years when natural gas shot up I started keeping track of where the stats had to be according to the outside temp. It used to be I would set it and forget it but thoses days are gone. You just start out high and work your way down to where at a certain temp the stat will be here. ie: warmer days at the one wash such as high 20s, the slab stat would be on 35-36. When it will remain in the mid to low 20s dueing the day and even colder at night it will be on 38. Colder it will be on 40. 40 is about the highest I have to go at this wash. The stat with the return liquid I set on 36, 40 or 45. It is rare I go to 50. When they first installed this stat they told me to keep it on 70. I did until the gas prices soared. I did notice at 70 my IBA floor was pretty much always dry or steaming which told me it was too high. The other wash is a different story. You just have to "play" with each one until you have it down I guess. I keep a note at each stat where it needs to be st a certain temp. I only use 3 settings most of the time. If it is going to get and stay that cold for a few days like in single digits, I close.

 

[Andyjmyr]

Bud,

I see what you're saying about the floors dry and or steaming. Right now, we're doing pretty much the same thing you're doing. We currently look at the forecast for the night. Tabular forecast are the best for us because they tell us what time the temp will be 32 degrees.

The utility company here just passed a price rise in natural gas so conserving energy is more important than ever for us.

the boiler we have is usually set at 75 or higher for the (high), 65-74 for the (medium), and 64 or lower for the (low).

One of the biggest problems we face is the fact that our S.S. bays sit at one side and the autos on the other side of our equipment room. The last three S.S. bays always freeze up and or show a slab temp of 25 or lower. We've just made it a policy to close the last three bays during freezing nights.

 

[Andyjmyr]

OOOOOOOooooooo......

Forecast for our city.....


Overnight: Snow and sleet likely. Cloudy, with a low around 13. Wind chill values as low as 3. North wind around 17 mph, with gusts as high as 28 mph. Chance of precipitation is 60%. Total nighttime snow and sleet accumulation of less than a half inch possible.

Monday: A slight chance of snow before noon, then a slight chance of snow and sleet. Cloudy, with a high near 23. Wind chill values as low as 1. North wind between 11 and 16 mph, with gusts as high as 24 mph. Chance of precipitation is 20%.

Monday Night: A 20 percent chance of snow. Mostly cloudy, with a low around 17. Wind chill values as low as 6. East wind around 11 mph.

Tuesday: A chance of snow, freezing rain, and sleet. Cloudy, with a high near 30. Wind chill values as low as 5. Southeast wind between 8 and 11 mph. Chance of precipitation is 50%.

Tuesday Night: A chance of snow, freezing rain, and sleet. Mostly cloudy, with a low around 25. South wind around 7 mph becoming east. Chance of precipitation is 30%.

Wednesday: A chance of rain, snow, and freezing rain. Mostly cloudy, with a high near 31. Chance of precipitation is 30%.

Wednesday Night: Freezing rain and sleet likely. Cloudy, with a low around 28. Chance of precipitation is 60%.

Thursday: A chance of rain or freezing rain. Some thunder is also possible. Cloudy, with a high near 50.

Thursday Night: A chance of rain and snow. Cloudy, with a low around 31.



Living in the mid-west....Gotta love it!

 

[Bud]

Midwest here also. Never a dull moment. If you don't like the weather, wait 24 hrs. Then you may really not like the weather. Andy, have you tried cutting back some of the runs that do well to get more heat to those 3 bays? Sometimes this is a big paine but might work. I have similiar problems at our one wash. The North wall of the IBA will get ice on the floor about 2 to 3 feet out but everything else is fine. I have tried adjusting the other runs and the only thing that works is turning the thermo up which I normally won't do. I just salt that area unless it is staying that cold and still may be busy then I crank it up a bit. I don't worry about the IBAs like the SS bays but there is still the fact that people can exit their cars in the IBA plus you don't want it so bad the cars slide. I have been going to borrow a thermal imaging device from the local FD and find out which run/s I have the problem with and then test them (in the Spring) to see if I may have a blockage. Usually when there is an are that has an icing problem it means that run is too long which I think is what is wrong in my case but adjusting the other runs should help and it doesn't so I am hoping there is a small blockage in the line and I can blow it out. Good luck.