What temp do you run your floor heat boiler?

[6t7gto]

As the title states...what temp do you have your floor heat boiler set at?
I had my Raypak 514k btu set on #4. Manual says it is approximately 155*.
My boiler has sooted up on me and I need to clean it.
I lowered the setting to #3 (145* according to the manual) and it went down to 16* Friday night with a pretty good snowfall.
The floors are clear and dry.
I have a switch on my boiler to control the circulating pump either manual or automatic.
When it is forecasting low temps I switch the pump to manual.
When my system was originally installed a slab sensor was used.
We got poor results. So the contractor installed the slab sensor in the return manifold.
We use the stat for that sensor as a reference point of the return glycol.
Presently have this stat set to 65* to turn the burner on and off.
Thx
David

 

[2Biz]

I think you won't get answers as to one size fits all. You don't want to run a non condensing boiler at the same temperature as you would a condensing boiler. Non Condensing has to be ran at above 140° (I believe) to keep it from condensing and self destructing with highly acidic condensate! I have a Condensing Demand heater I run at 105° with a Primary-Secondary plumbing configuration. Fluid circulates to all the bays 100% of the time below 32°. A t-stat monitoring return temps fire the pumps to the demand heater. The differential is set @ 15°. The demand cycles on at 55° and off at 70°. When the 55-70° fluid mixes with 105° heater temp, about 90° temp fluid goes back out to the bays to keep the bays ice free (About 35-40° slab surface temp). At 32°, the demand heater cycles on for 15 minutes, then off for 15 minutes. The colder it gets, the longer the demand stays on. But its always on a 30 minute loop! That's the interesting part! I've watched it even down to -16° and the demand still cycles off at those settings. But is more like 22 minutes on - 8 minutes off. The settings never have to be adjusted and self regulates with temperature change in the slab. I haven't touched the settings since it was installed 4-5 years ago. These settings give me the most economical NG usage while keeping the bays ice free no matter how cold out.

Basically, yours is set up similar to mine at firing the boiler at 65° return temp. Good move to put t-stat in the return line instead of relying on a slab stat. Much more accurate and can be set easier to minimize NG usage while keeping bays ice free.

 

[PaulLovesJamie]

I think my setup is very similar to 2biz' - condensing instantaneous heater, primary/secondary configuration.

I turn on the system around thanksgiving, and I run the loop circulator when the outside temp is below 60. (I want to be careful that if we get a really warm day when the floors happen to be cold, I dont want the boiler to fire if the loop circulator isnt running.)
At that time, I set the heater to run when the loop return temp drops below 50.
I run the heater at 120.

Then I adjust it based on the weather:
When we get sustained weather below freezing, I nudge that up to 55.
If it is going to be below about 15, I nudge that up to 60, and bump the heater up to 140.
If it is really cold and we are very busy, I nudge it up to 65 for a few days. (wet floors need more heat)

My goal is to keep the bay floors around 40.

 

[PaulLovesJamie]

These settings give me the most economical NG usage while keeping the bays ice free no matter how cold out.

2biz, I set my heater temps basically by trial (without error, lol - I erred on the high temp side). But I really dont know if I could be more efficient, I adjust my temps based on the weather to try to squeeze out more efficiency.

It would be nice to lower my temp to 105, set it and forget it.
Do you recall how you came up with those settings?
Did you find a calculation somewhere to figure out the most efficient settings?

 

[2Biz]

I didn't use any kind of calculator... Coming up with something that worked as efficiently as possible was through trial and error.

My system is energized off the auxiliary output on the weepmiser @ 32°. Basically energizing a 20a 120v relay that powers the loop circulator, the (2) circulators (In Series) feeding fluid to the demand heater, and also powers the Raychem Heat Tape in the trough. The loop circulator runs 100% of the time below 32°. The (2) circulators feeding the demand heater are fired by a T-Stat monitoring the return temp of the loops. It fires the (2) pumps at 55° return temp and turns off at 70°. With the Demand set at 105°, I never have to adjust anything to maintain a 35° - 40° slab surface temp no matter how cold. The colder it gets, the longer it takes to get to 70° return loop temp and the quicker slab temp drops to energize the pumps again. Even down to -16°, the pumps to the demand heater still cycle on and off. So it is basically infinitely variable by design and works perfectly.

With the 15° differential set in the zone return T-stat, It took me a little while to get the minimum setting to keep the bays ice free. Since the Takagi has input temp, it was really easy to set the return t-stat based on the cutout temp the heater was displaying. If the slab surface temp was a little low after it stabilized, I'd raise the return Zone t-stat about 2° (Verifying cutout temp on the Takagi) and check the surface of the slab with an infrared gun to also verify the changes. I did this a few times till I got it just right and haven't touched it since.

I selected the 15° differential in the return loop T-stat so the demand heater wouldn't short cycle. 15 minute on - 15 minute off seems to work great!

BTW, I don't turn on my system untill I know the temp is going a few degrees below freezing. Even then, it doesn't come on till the weepmiser hits 32°...Maybe you could set yours up the same and save some $$$. Sounds like there is room for improvement.

 

[Roz]

I believe our installer set our 30 year old boiler to run at 160deg, however my temperature gun says the outbound tubes are 90 and the inbound tubes read 70. Probably too high however we do not have any icing issues for the first time. We did redo our entire loop system and floors with 12" spacing which provided us an extra line in each bay. We also add lines to our 8' entrance apron which we converted from asphalt since people spray water everywhere. Customers have noticed the difference and commented on the floors.

 

[6t7gto]

Roz,
Thanks for the idea of checking the outbound and inbound temps.
Its 27* here now and snowing.
My floors are wet and the temp is rising over night.
But I'll check the lines in the morning.
David

 

[6t7gto]

Pic at 8pm tonite.

 

[Roz]

We also adjust the flow in each bay as each bay is on an individual loop. Closest bays to ER are 1/2 open, then 3/4 and furthest bay is full open. We have 6 bays, 3 on each side of the ER. Helps get extra heat to furthest bays.

 

[wash4me]

There’s usually a bypass loop so the boiler temp is higher than the loop temp. This is necessary to keep the boiler from condensing.

 

[wash4me]

65 is my normal return temperature. If it gets below 10 degrees air temp or so ice will form. If we are going to close the wash I just let it run at 65 knowing that is soon as it warms up the ice will go away immediately because the slab is almost warm enough. If we are going to stay open I just turned the return temperature up to about 75 and it’s never gotten cold enough that that would not get rid of all the ice. if we are going to close the wash I just let it run at 65 knowing that a soon as it warms up the ice will go away immediately because the slab is almost warm enough. If we are going to stay open I just turn the return temperature up to about 75 and it’s never gotten cold enough that would not get rid of all the ice .

 

[PaulLovesJamie]

Maybe you could set yours up the same and save some $$$. Sounds like there is room for improvement.

Thanks for the detailed response, and there's always room for improvement for me
I wish you had done your project a year sooner, you would have saved me some $ and a lot of figuring. We were doing ours at about the same time, but I did get a few tips from your epic floor heat install thread, you were a little ahead of me.

Sounds like the main difference is that you run your return temp a little higher than I do, and the boiler temp a little lower. I might try that and see how it works for me.

I honestly dont know how to calculate which is more cost efficient - gas usage is too variable for me, degree days of heating vary, wind chill, customers sweeping snow off their cars, etc. But - I know my geothermal system (at home) is designed to run a lot, move small amounts of heat for longer periods of time, I'm told its more efficient that way. So I suppose thats a data point.

btw, if I set my return temp at 70 I'm also good to go, zero ice and steamy bays. I nudge it up/down based on the forecasts to try to improve efficiency, I think it saves me $ without compromising bay temps.

Another thing I dont know is exactly how many gpm I flow through the loops - and I also dont know how many gpm should flow through them, ie what is the right flow rate and volume for optimal efficiency. I use one taco 013 and I should be fairly close to its max flow rate of 34, but I havent measured the actual flow... and I as I said I dont know what it should be. It is working really well though, I just want it to work better

Other info for others who might be reading this:
I also use an IR thermometer to check bay temps, a lot, like every time Im at the wash.
I dont use the weep mizer, I use a taco zone controller in combination with johnson controls A419 temperature controllers (aka thermostats)
I do not have a slab stat, I'm monitoring the return loop temp.
I replaced my crappy bay loop manifolds with nice ones from supplyhouse, flow to each loop can be monitored and adjusted. Adjusting flow to individual loops made a noticeable difference.

 

[2Biz]

I recall reading somewhere that you don't want too much flow through the loops to get good heat transfer. I think you only want about 2-3 gpm per loop. Any faster than that and you will short cycle the heater. So the Taco 013's flow rate of 34gpm worked out about right for my 5 loops (includes one trough loop) and all the fittings calculated.

You never said, do you have differential set on your return loop t-stat?

I don't run my return temp higher than yours. When return temps reach 55°, the return t-stat turns on the pumps to the demand...When return temps get to 70°, the pumps cycle off. Have you ever timed the on-off cycle at like 25° to 30° outside air temp?

 

[PaulLovesJamie]

I recall reading somewhere that you don't want too much flow through the loops to get good heat transfer

Agree, I read the same thing.

You never said, do you have differential set on your return loop t-stat?

Yes, but I have it set to 5 degrees. I recall from the 70s/80s when "setback" thermostats became popular, that in practical application having wider temp swings actually used more energy, and lots of people ripped those thermostats back out. That was definitely the case for me in the 80s, my house was cheaper to heat if I kept it at a steady temp.
So thats why I chose a lower differential.
Not saying I am right, just that was my experience so thats why I chose that setting.

I don't run my return temp higher than yours. When return temps reach 55°, the return t-stat turns on the pumps to the demand...When return temps get to 70°, the pumps cycle off.

When mine is set to 55, the pumps cycle off at 60; I almost never get up to 70.

Have you ever timed the on-off cycle at like 25° to 30° outside air temp?

Not yet
But based on your comments here I will be doing that, as well as digging into the differential settings a bit.

 

[2Biz]

Paul,

My guess is we both have our systems about as efficient as we can get them, even with different differential set in the return T-Stats...Mine is 15 minutes on - 15 minutes off. I bet yours is 5 minutes on - 5 minutes off. Basically the same in an hours time.

About the only suggestion I can offer, is use output 2 on the weepmiser to energize your system (With a relay) at 32°....There are a lot of nights my system doesn't run when temps are between 32° and 50°. If I understand correctly, yours will. If you put the zone circulator AND the pumps to the demand heater on the same circuit activated by output 2 on the weepmiser, you'll never have the issue you describe in the 3rd post in this thread. I've never had a slab freeze with this setting. Output 2 on the weepmiser also activates the blowdown/washer fluid injection system for all low pressure hoses. Also have never had a freezeup of the LP hoses at this temp.

Something to consider...

 

[mjwalsh]

We are using condensing boilers from Hydrotherm Hydropulse. The brochure when brand new was saying that a church with far reaching old cast iron radiators that would allow the return temperature to get as low as possible would greatly increase the boilers efficiency. So we try to make the return fluid go as low as possible especially during -50° F wind chill without getting into slip & fall danger. Hydrotherm quit making those boilers back in 2006 so I am not sure what condensing boilers sold now would be somewhat their equivalent.