Boiler floor heat system

[koditten]

I should start with the basics. Highly insulated building with cathedral ceilings. Around 800 square feet of floor space being heated, 2" foam board under concrete and around perimeter, 3 loops of tubing with each run about 250'. 2 9X9 overhead doors and 3 windows and an 1 access door.

I started the boiler (55k BTU) with the floor at 52 degrees. In 5 hours the slab temp is up to 71 degrees. After running the system over night the slab temp is at 77 degrees. The building ambient temp is running at 58 degrees. This is actually warmer than I want so I turned the thermostat down to 58 degrees, the stat was previously set at 65 degrees. I spent the day working in the shop moving cars in and out and I only noticed the boiler turning on 4 times and each time it ran, it only ran for an estimated 10 or 12 minutes. If this thing works half as well as I hope I am going to be one happy camper.

I have included a few pictures of my system

 

[Fastback]

Cool, do you know what kinda flow rate it's running at?

 

[koditten]

I have flow indicator wheels showing my flow to each loop. Of course with a boiler you need two pumps or a bypass loop. I chose to use two pumps, they are cheap. The wheels show how much water is flowing at one time, unfortuntely there is no gauge showing the gallons/min.

Buy estimation, I think my primary loop, this is the loop that recuculates the water to the boiler is runing at 75%. Remember you want the boiler to stay near 180 degrees or a bit warmer. My secondary loop is only running at 25%. With this set up I get a floor supply temp at 108 degrees. This combination keeps my boiler from short cycling. So far I have only notice the boiler turn on for less than 10 minutes per 4 hours total.

Both pumps are rated at 8 gallons/minute.

I 'm pretty excited on how well this system works, my only concern is the gas bill, which doesn't show up for another 22 days. I will definately be comparing it to last year. Stand by for updates.

Later
Kirk in middle Michigan

 

[Fastback]

My system will be on demand electric, so I am trying to guesstimate how much flow others see so I can determine some things.

Did you staple the PEX down to the foam board?

 

[koditten]

Fastback:

My pex tubing (1/2") is sitting directly on the foam board. I used these clips that screw into the foam board. I don't remember what they cost but they were gerat to use. I got them at Menard's. They are made of plastic and it was less than 30 bucks to do my whole floor.

 

[nate379]

It's weird you have that kind of recovery time with that setup.

With my 90,000btu boiler and the water to the floor temp at around 120-130* it takes what seems forever to get the garage up to temp after I open the door for more than just a few seconds.
Slow enough that I have considered even adding a force air setup for a quicker recovery.

 

[koditten]

I agree, it's wierd. I may have been hitting the floor loop with a bit higher temp than I previously stated. I was using my IR theromoter to read copper pipe temps, floor temps and cast iron fitting temps. What I originaly thought was 104* was actually 120*. I got to wondering why the copper pipe was reading 104 and a cast iron fitting on the same line was reading 15* warmer. It turns out that different colors and surfaces reflect the temp differently. I solved this by putting making tape "test points" on my pipes as well as in various areas of the shop. This way I was able to get proper readings with the IR thermometer. Now, I really do have 104*+/- supply to my manifold.

All I can say presently, is I am very excited on how well this heating style is working. When I started the system last week it was still quite mild for Michigan. I was thinking this may be part of why it was responding so well. Well now we have had negitive overnight temps for the last 24 hours and it is still quite comfortable. I actually turned the temp down to 48*. I'm working now so I can't check things out several times a day like I want to. I 'm just going to have to wait for the gas bill. This will be a valid test though. The outside temps right now are worse than in Jan/Feb.

I do know my water is moving at about 1.5 to 2 gallons/min. That volume is split up between 3 loops. That water is giving up almost all of its heat to the floor. Nate379, If you can, try pinching back the flow to your loops.

 

[nate379]

I can adjust the flow rates on all my circuits, right now they are all wide open. That not correct?

 

[tdkkart]

I can adjust the flow rates on all my circuits, right now they are all wide open. That not correct?

As long as your boiler/heater can recover the water temp, runnig the loops wide open is fine.
The question is, how much heat drop are you getting from in to out in each loop. The "experts" recommend approx. 20* temp drop from in to out.
Alot of variables here though. I've got mine throttled back a bit because of the recovery rate of my heater.

 

[buddyboy]

Have you guys thought about recording the outside temp. when making your other measurements?

has anyone ever tried setting up an outside thermostat to work with the indoor one to help regulate slab temp. according to outside temps?

 

[koditten]

Nate:

I have my secondary zone, the zone with the loops in the floor, throttled way back. My primary zone, the zone for the the boiler, is running wide open. By my rough calculations I belive 8 gal/min for the boiler and 2gal/min for the floor(3 250' loops). When I put my pex down I made my 2 outside loops around 6-8" apart. My inner loop varies from a 1' to 18".

With this I am able to keep my boiler water around 180* and my floor water around 100*.

I have been recording outside temps as I run my system. We have been at lows of -9* to mid 20's. I don't spend every minute of ever day out in the shop, but the temp has maintained my 50-55* that I have set the thermostat at. I honestly don't notice the boiler running much more when it is really cold.

One thing that I have noticed is when I use my small wood stove to burn scrap wood, it does screw with the floor system. I think I will move my thermostat closer to the floor so as to not be so affected by the little bit of heat generated by the wood stove.

I have looked at the outdoor rest units. I am extreamly happy with the way my system is working as it sits. If this was attached to my home I would definetly have one. Lets face it, if the shop was perfect I would never go in to the house and see my wife.

 

[matt60j]

Where did you get your boiler? I'm in Freeland over by MBS airport btw. I have 2000' of pex in my 40x56 barn. 6 loops 2 zones. Trying to educate myself so I can keep plugging along with the progress. Your right, it has been dam cold for this time of year. -MATT