View Full Version : Huge gas bills!!!
01-16-2011, 01:57 PM
I recently built a 1500sq' shop with in-slab heat supplied by a Munchkin Contender MC50. The boiler seems to be running alright but I'm going through about $800 worth of propane a month!! I noticed when my contractor poured my slab that he didn't raise the rebar/tubing to the center of the slab. So by having the tubing near the bottom of my 6" thick slab could this be why I'm going through so much gas? I made sure to put down 2" ridgid styrofoam under and along the sides of the slab. The boiler is just controlled by a cheap thermostat and there is no outside reset. The plumber who installed everything said it should work great the way it is??? I'm not sure he even set the boiler up correctly given his short answers and telling me it should be fine. Is there any info I could gain before I hier a new contractor?
01-16-2011, 02:15 PM
The $800 seems a bit high, what is the price of propane in your area. The contender can deliver on full fire about 31 btuh per square foot. Are you over heating the space, what was the r value for the slab and perimeter insulation. As far as the tubing being low, there is not much you can do at this point. Your climate conditions obviously play a huge role as far as your bills are concerned.
01-16-2011, 02:17 PM
you have to look at how much do you pay per gallon of lp. it is not cheep to run a lp sys. if it is not a new install i would look into having your boiler cleand. i know the munchking boilers that run lp get durty quick b/c lp is durty
is long as there is inslahon under the pored slab it shood be ok. this also has ben a cold winter as well with a lot more dergre days then last year. and if this is a shop you have pepole comming in and out alll day long this will increas the btu s needed for this space you also could have a pro check the gas preshers to make sher it is not over fiering and make sher you are not overheating the floor this would be a wast of heat
01-16-2011, 02:24 PM
Propane is running around .60cents a liter and last month they topped my tank up with 1000 liters. Outside temps have been ranging from -10c to -27c for the last month. I had the thermostat set at 12c which is pleasant by after my first bill I have dropped it to 5c, hoping to save a bit. I can't remember what the r rating for the foam was I think around 12 and both walls and roof have R-40.
01-16-2011, 02:32 PM
Brand new install been running for only a couple months no problems with the boiler (as in error codes) Could the contractor have missed something when setting up the boiler or maybe something wasn't set properly?
01-16-2011, 02:37 PM
so it is inslated under the floor so the heat is going up sounds like it was installed right. i would have the temp going out to the floor and gas checked by a pro. but your oda is cold i live in RI (USA) i know houses that burn more lp then that around the same sq feet and the coldist it has be around hear is 10 f
01-16-2011, 02:58 PM
you should step back and look at original design, tube spacing, slab design temps, insulation r values etc. i dont know these celcius numbers, but radiant should only need to heat to somewhere in the 65-68 f range to be really comfortable. if your tubing is near the bottom it will work harder to heat, should be on chairs or tied to rebar on chairs. water temps shouldnt need to be real high, where are you running? finally if water temps are too high, as in not using outdoor reset, you are not running your boiler efficiently. with a "cheap thermostat", you could be simply cycling the boiler on/off at high temps, which is inefficient as compared to running on a reset schedule and utilizing the condensing temps for higher efficiencies. need much more info, or you need a real pro out there.
01-16-2011, 04:07 PM
The tubing is 1/2" with 5 runs 300' each spaced 12" apart grundfos circulating pump set on medium. No mixing valves, no outdoor reset. A couple of things I think would help? The temp was set at 55f on the thermostat for the month which is good for me. Just my truck out in the morning and back in at night no huge loss of heat during the day. The boiler runs between 90f and 100f when the thermostat is calling for heat. It runs for long periods of time which is understandable cuz it's such a big mass. I think I just need to maintain a constant temp instead of the thermostat dropping 2 degrees and taking an hour to bring it back up. This would be accomplished by having the outdoor reset??
01-16-2011, 04:32 PM
how big is your truck b/c you truck is a big heat load as well thaking that into the bilding every night after being out in -23f to a 55f room it is cooling of that room a lot this is probly your heat loss leave the truck out side and put a oil heater in the oil pan of the truck
01-16-2011, 05:05 PM
Was the building sealed? You might have more air filtration then you think.
The boiler may not be burning right, was it checked with a combustion analyzer, or just turned on.
And at $2.271 US a gallon for propane, thats not cheap. And means you used 352 gallons a month. or 11 gallons a day. So the boiler would be running an average of about 19.5 hours a day.
01-16-2011, 05:28 PM
Since this is a new installation, it is possible the propane tank is leaking?
:callpro:if it comes to hiring a new contractor make sure you sellect a HVAC. contractor, not a plumber. no disrespect here.
01-16-2011, 06:03 PM
I honestly don't think my plumber has the right equipment/tools for this type of job. Even though he assured me everything was done correct. Not being around for the initial startup I don't know for sure. I'm currently searching for a new contractor/ serviceman/ tech but living in a small town really limits the people and options. I'm not saying I want to do any of this myself just need some help pointing the local plumber in the right direction. Thanks for all your help. The tank and lines were inspected 3 times to check for leaks, that was all good. As far as being sealed I think my weakest link would be the 2 10x10 overhead doors and the weather striping used but there's no really bad areas of heat loss. It baffles me that my neighbors down the road have practically the same size shop, boiler, insulation etc but he uses Natural gas and his bills are $100 a month. More or less the reason I went with the same setup??? My brain hurts this stuff is frustrating
01-16-2011, 06:14 PM
bet the ground under the barn is warm....maybe not enough insulation there, especially with the tubing in the bottom of the pour. so is the pump running constant circulation or cycling? does it really need to be 55 in there just for your truck? if you dropped it to fifty, it would still be decent in the morning, and save you a few sheckles.
01-16-2011, 06:19 PM
Where is the stat? On an outside wall? What kinda stat is it? Is the placement away from drafts (doors, windows........)
Does it ever get too hot in the shop?
Did you ever take temp measurements of the slab itself? Did he put temp sensors in the slab?
I would have the boiler tuned by an authorized tech from the companies web site.
01-16-2011, 06:28 PM
i keep my house at 54f and i have a 1000 sq foot house and when it is between 1f and 10f out side my gas bill is 120 to 150 and i have a 93% furnace
and if you say this a shop with a 10x10 door and you bring you cold work truck in after leaving it out side all day when your oda is -23 i can see why your bill is 800 a month
it is like taking a turkey out of the oven every day and puting in the freezer and not thinking that you bill to run that fridge is not going to go up
i would have it looked at buy a pro and have him tell you whats rong with it find some one that works on radent heat a lot :callpro:
01-16-2011, 06:35 PM
Did the contractor leave any instructions? What is the ceiling height of you shop?
"Modulating Combustion System:
Modulation during the central heating
operation is based on the supply temperature.
The set point used for the control depends
upon the programmed central heating curve.
The slope of the heating curve can be changed
by the installer of the Munchkin Contender in
the sense that both turning points of the curve
can be moved. The control monitors the
system to regulate the output of the burner
during operation to match the system
demand. This increase in efficiency allows for
substantial fuel savings"
This adjustment can be made by you. Maybe you just need to call the manufacturer and ask who can come to your home and check the installation. Like I said get a factory authorized service tech.
01-16-2011, 06:58 PM
did some calculations and agree with beenther post. you are burning 11 gallons of propane a day on the average. the price of propane is correct, the btus of the boiler is sized correctly. the unknowns are the infiltration losses, doors, windows, and the slab loss which could be calculated with more information. considering how cold this winter has been , your bill may not be as high as you think, more info is needed .
01-16-2011, 07:42 PM
The current thermostat setting is 40f which is fine but still using a fair amount of propane. The ceiling height is 12 feet and the thermostat was located right near the big door which I moved immediately after he installed it. It's not near any windows or doors but it is close to where I park my truck and I notice as soon as I bring it in the temp drops 2-3 degrees. There were no inslab temp sensors installed how else could u get readings from the slab? I have one of those temp guns that give u a digital reading, are those slab sensors supposed to relay back to the boiler?
01-16-2011, 08:18 PM
You said the system had a grundfos pump.... just 1? What's the model number?
Is there antifreeze in the system? Do you have any idea what concentration?
Did you look at the installation manual for the boiler? It shows in there exactly how a few different systems should be installed.
Pictures would be worth a thousand words on this one.
01-16-2011, 08:49 PM
Grundfos type ups 15-58FC I think that is the right number, and yes just one on the supply side. I will try and get some pictures up right away maybe that can help
01-16-2011, 08:56 PM
I am running about 60 water 40 glycol
01-16-2011, 10:27 PM
Turm it off and install a little 60K 95% furnace and see how that goes. I have a feeling the slab insulation is heating the ground.
01-16-2011, 10:34 PM
:callpro:if it comes to hiring a new contractor make sure you sellect a HVAC. contractor, not a plumber. no disrespect here.
Up here it is us plumbers that do hydronics.
01-16-2011, 10:36 PM
How far can we take this in our (non pro) open forum?
01-16-2011, 11:00 PM
A Munchin must be set up with a combustion analyzer for LP, if it wasn't it may be not achieving efficiency, and will void warranty. Also if the return water is too warm the boiler cannot operate as a condensing boiler, which lowers it's efficiency. As you and others have mentioned, you need a tech who knows munchkins. They also need to look at outlet temperature, if it is too high, your back losses (to the ground) will be high.
01-17-2011, 12:10 AM
I suggest that you look at the installation manual for your boiler. Pay attention to the piping diagrams where it shows how they want that boiler installed. An installation option of a single pump was not one of the options they list.
With the information that you've provided I did the math and you're flow through your system is going to be one of the problems you're having. The other issue I'm going to guess is the installer did not have or use a combustion analyser to set the boiler's firing up correctly.
Antifreeze in a hydronic system protects it from freezing but it also introduces variables into the design of the system that if not addressed will cause the problems you're having.
You need to find yourself a trained and experienced radiant heating contractor to help you fix your problems.
01-17-2011, 06:22 AM
Several thoughts after running some modest calculations. You said the walls are insulated to R40 along with the roof, are there any windows and are the doors insulated as well. Your boiler is obviously sized large enough because you are not complaining of comfort. This brings us back to the shell and slab insulation. Another thought which can not be overlooked is the groundwater table below the slab. If you live where the table is high a tremendous amount of heat can be lost . As mentioned earlier, the radiant temperature should be as low as possible to improve the efficiency and lower losses that may be occuring through the slab. I assume this is a free standing building, if not and it is adjacent to another structure, the slab could be leaking heat into the slab or walls of the other structure. We know by your bill that the boiler is firing on the upper end of it modulation for good period of each and every day.
01-17-2011, 08:05 PM
You have 60 tons of concrete to warm up BEFORE it starts to "contribute to the warmth of the space at 2 BTUs per SF per degree above the room temp you are looking for ( if it is pumping and working.
Are you trying to set back the unit at night and not just getting the slab to temp? You now have a big tanker and not a motorboat that will turn on a dime.
01-17-2011, 08:23 PM
You also said the thermostat is set @ 40. Why so low? I would also think a mixing valve would be needed on the system. Did you call the factory today?
01-17-2011, 08:42 PM
I was looking at the install manual for the boiler, I recall somewhere only one pump was mentioned. I need to look at pump selection, but at a maximum of delta t of 35 the boiler has 2 ft friction loss at 2.5 gpm. Also you mentioned that the glycol mix was 60/40. There would be a output loss of about 25%, not to mention the increase head against the pump. I am starting to believe that there is more than one problem here. A diagram and pictures would go along way.
01-17-2011, 09:23 PM
I dropped the the temp down as low as it would let me about 40f hoping to try and save on my gas. Having the cold truck in there everynight, the less it energy used to thaw it out the better?? The shops main purpose is for my vehicle, and after 10 years of parking my rig in the cold this year I was grining ear to ear. So even if it's barely warm that's good for now. Would I like it to be 55 or 60 absolutely. Maybe I can accomplish that by next winter. This year I'm going to get the boiler dialed in by a professional with a combustion analyzer, check for air leaks. This summer I'm going to change the thermostat to something that's more compatable with radiant heat, install some mixing valves, and an outdoor reset. So far that's what I got from all the great replies thanks everyone. So only one pump was installed another would be beneficial? I'll get pictures up asap.
01-17-2011, 09:32 PM
Recheck the pump model, it did not appear in my engineering binder
01-17-2011, 09:45 PM
the model of the pump is UP(S)15-35 got it right off the pump and the manual says the same??
01-17-2011, 09:57 PM
heres some pics lemmie know if more will help
01-17-2011, 10:42 PM
Not too bad overall, I can only think of about 12 things I would have done different with the piping.
I would guess you have a UP 15-58 pump there.
Its doubtful you have enough flow thru the boiler with that set up. Primary secondary piping is preferable.
01-17-2011, 11:09 PM
I would have to agree with chuck, the primary /secondary is a must after looking at the pictures, flow rate has to definately be a problem. do you know how much lineal footage of pex is in the slab. still digging into pump curve.
01-17-2011, 11:18 PM
There's not much right with the way the installation was done. The manufacturers put the pictures in the installation manual for a reason. If the installer won't take the time to read how it's supposed to be done or go to the schools put on to learn, they hope that at least they'll look at the pictures.
I love the pressurized makeup water tank sitting on the floor though. :LOL:
You really need to find an expert to come in and fix it. Anything said beyond this point would verge on giving out DIY information that isn't allowed by the rules in the open forum.
01-17-2011, 11:20 PM
I don't mean to be rude, but I see multiple problems with the system in the pictures. You really need a qualified person to straighten it out.
01-18-2011, 12:04 AM
find out who did your neighbors garage and get him to come look at it
01-18-2011, 06:38 AM
I looked into the pump and did some rough calculations. I am curious if there is a pressure relief valve installed and if so what is its rating. Several things are going against you. The pump selected is rated at maximum temperature of165 F , the flowrate necessary to overcome friction loss is close to if not outside performance capabilities. The boiler comes factory default at 180F, hopefully this has been changed. You are in need of a professional hydronic heating contractor to correct multiple problems that do exist. Your system can never perform correctly until some changes are made. In fact you may have some safety issues that need to be addressed.
01-18-2011, 11:15 AM
Just to be clear I understand the rules of the website, I'm not on here for DIY advice but mearly some insite to what/where the install went wrong. Information gained here will be for my own protection so that the next guy that comes to look at it cant tell me that "it supposed to be like that, its fine" I guess it all goes back to my initial concern and that was the amount of gas I was going through. Does the bad design of the piping affect the amount of energy I'm using? I realize that any hydronic professional would know exactly what to do but in my case people of that profession around here are few and far between. Local plumbers with 20 jobs on the go is what I'm limited to. To answer a previous question the lineal footage of 1/2" pex is 1500'. The highest temp I've seen since the boiler has been running is 100f and 90% of the time it's at about 77f on high fire while the pump is cycling. It drops down to 70f when I put the pump on high. It seems as though it's cycling fine??? By that I mean not overheating the water enough to damage the pump.
01-18-2011, 11:52 AM
Like a previous posted said, find out who did your neighbors garage and talk to them. Be it a plumber or a heating contractor what matters is finding someone that is trained and follows the installation instructions of the equipment they're installing.
I've spent over 25 years gaining the knowledge and experience I use when I get called in to "fix" a system that isn't performing to the customer's expectations. Yours, from the pictures, to me looks like a simple fix. Cheap fix? I'm going to guess not when it comes to how you'll perceive the cost. But what it will cost to fix is what it would have cost (plus the demolition costs of taking out what's there) in the first place if it had been done right the first time.
All the professionals here realize you're just trying to gain the knowledge so you can be a better consumer when the next person looks at it. Can we educate you here in this forum well enough so you know for sure they know what they're talking about or not? No.
I will again say, look at the installation manual that came with the boiler. Very little if anything you have shown us in the pictures is close to what the manufacturer requires for a proper installation of that boiler. The installation has written all over it (by the installer) "I can solder pipes together and do basic wiring, but I either can't read or understand pictures or I just choose not to! Besides, putting in boilers and radiant heating systems isn't rocket science!"
With that off my chest :whistle: ......... if the next person (that comes recommended by someone that's very happy with the radiant system they installed for them) walks in and says "This system isn't installed according to the manufacturers recommendations, because..........." . And they will spend the time to show you in the installation book where things are done wrong or missing and spends some time explaining pump curves/capacities and temperature drop............. Hire Them!
Whatever it costs to get it fixed will more than likely be more than saved in savings on fuel costs not to mention the longevity and potential maintenance issues down the road with the boiler itself.
The warranty is (in my opinion) void at this point on the boiler because of the way the boiler is installed and the assumption that your installer did not do the required setup with a combustion analyzer when he fired it up. And that's just two of the reasons. Another thing you can find in the installation manual or other paperwork that came with the boiler......... reasons why the manufacturer will NOT honor the warranty on the unit.
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