Is my Gas Usage Normal?

wanttolearn

Hi-

I was wondering if someone out there could help me analyze my monthly gas bill to see if everything is normal the way it should be.  I will try to break it down for you:

In the depth of winter, my gas bill shows consumption of approx. 900 terms per month (cost approx. $1,000!).  Although they are NOT shown seperately on the bill, here are the various items in my house that use gas:

1.  I have a Peerless 6409 steam heat boiler.  The unit size is 460,000 BTU.  I would estimate that the unit is on for approx. 10 minutes per hour, which equals 4 hours per day, which equals 120 hours per month.  Approx. how many therms should this consume?

2.  I have auxilliary baseboard heaters running in two rooms.  I believe they run on hot water.  I would estimate that there is a total of 30 linear feet of baseboard heaters.  This unit is on the majority of the time in winter  (I would guesstimate it is "on" 70% of the time).  Again, is there a way to estimate what therms usage this causes?

3.  I have radiant floor heat in one single bathroom of approx. 150 sf.  This floor heat runs off of hot water directly from my Peerless gas boiler.  This system is very weak, and even though I set the thermostat to 72 degrees at all times, the room rarely get over 70 degress.  So I assume that this radiant heat is running 100% of the time, because it never reaches the target temperature.  Therms usage estimate for this?

4.  Lastly, we use gas for cooking, domestic hot water, etc.  Based on bills from summer months, This portion of the usage is estimated to be at less than 50 therms.

Deducting (4) from (1) - (3) leaves approx. therms usage of 850 for monthly heating, which seems very high to me!  I am trying to get estimates for each of (1) through (3), so that I can isolate where I have the most therm usage, and work specifically on that part of the problem, to get my heaing costs down.

Any help would be greatly appreciated!

icesailor

Normal usage:

Man, that must be one big hacienda to need 460,000 BTU's.

Do you know how many Sq/Ft of steam radiators you have and is the boiler sized to this or is it way too big? You need to have the boiler sized to the radiation with steam. Not the other way around as with water. I do a 46 bed nursing home that doesn't have boilers that are as big as that.

Mark N

Big Boiler

There are 100,000 btu's in 1 therm. Your boiler is rated at 460,000 btu's per hour. Every hour of total run time your boiler uses 4.6 therms. What heats the water for baseboard? You estimate 850 therms for heat a month. That comes to about 28.3 therms a day. Your boiler uses 4.6 therms a hour. That comes out to 6.15 hours a day. That isn't to crazy if it really cold outside.

wanttolearn

Reply

Thanks for both responses.  Regarding the sizing of the unit, I had several plumbers give me quotes on how big the unit needs to be, and they all came in at similar sizing, so I assume it is more or less correct.

I response to the second posting, I dont think my system runs for 6.4 hours per day.  I think it is more like 4 hours, or even less than that.

I personally suspect that the baseboard heater and radiant floor heat in the bathroom are causing a lot of the therm usage (maybe as much as 300 therms per month?)  Is there a way to estimate how many therms they use.  To the best of knowledge, both of them get their hot water from the Peerless gas boiler.  It's either that, or they get it from the dometic hot water heater, but somehow I believe that this would be a safezty hazard, so my guess is that they get it from the Peerless boiler.

Mark N

How long

Do you know how much it runs each day or are you guessing? If the radiant and the baseboard get their hot water from the boiler they are going to cause it to run also. I had my meter read 16 days ago. Since then I've used 115.838 therms. That comes out to 7.24 therms per day. Subtracting out my non heating usage, I come up with 6.19 therms per day for heat. My boiler uses 1.05 therms per hour so that comes out to 5.9 hours per day of run time. So I don't think it is out of the question that your boiler runs around 6 hours per day when it is real cold. Spend some time watching your boiler. See how long it runs on each call for heat. When it is cold see how often the tstat calls for heat? How long does it run to heat the radiant and the base board? Learn how to read the meter. Check it each day see how you use under different conditions.

wanttolearn

Further Reply

Mark-

i think I wasn't clear in my message.  My estimate of 4 hours per day is only for my actual steam radiators.  I can tell when this system clicks on and off, because the thermostat shows this.  I have watched it closely, and do not think that it runs more than 4 hours per day.

So by inference, that would mean that my auxiliary baseboard and radiant floor heat make the boiler run another 2.4 hours per day?  i.e.  approrx 12 therms per day?  is that possible for 30 feet of baseboard heat and 150 sf of radiant floor heat?

Mark N

Hard to say

I have no idea, I've never observed your system in action. I also have a baseboard loop off of my boiler. It has 20ft of cast iron baseboard. If I was to take a guess I would think it uses approx 1.2 to 1.5 therms a day. But I'm not sure. In your original post you state that the boiler runs about 10 minutes per hour. That seems kind of short to me for a steamer. It might take 10 minutes to make steam and just start to get it to the rads, Then another 10 to 15minutes to heat the rads.

Mark N

Quick Calculations

I did some quick math and came up an EDR of like 1150 sqft. That is a lot of radiators. Are you sure this boiler is sized correctly?

wanttolearn

boiler sizing

Mark-

I am not sure what EDRs are....but I as I said I had several plumber estimates and they all ranged from 340,000 BTUs to 460,000 BTUs, so it cant be far off the mark.  My house is 5,000 sf, and it has approx. 25 radiators, the smallest being approx. 2 sq. ft. and the largest as much as 10 sq. ft.  On average, I would say the radiators are 5 sf surface are.  At 25 radiators, that would be 125 sf of surface area.  Does this information make sense?

icesailor

Measuring radiators

Measuring radiators isn't rocket science. You take the radiator in question, identify it and decide how much each section gives out in Sq/Ft of radiation and multiply it by how many sections. You do ALL the radiators, each and every one that has steam. That equals how many BTU's or EDR the boiler MUST be wo make enough steam to do the job. Or, that's how I do it. Then, I do a total heat loss on the dwelling. I have found that the boiler will be grossly oversized for a HW load but not so for steam.

If you got a quote on 460,000 BTU on one quote and another was 340,000, someone or both didn't know what they were doing. It's one, or the other. Or, neither.

Measure them yourself. It isn't the size you measure. What you use is a rating.

wanttolearn

question to icesailor

Icesailor-

is there a BIG difference between a 345,000 BTU and a 460,000 BTU boiler?  In other words, would one size work well, and the other not at all?

being unexperienced in these matters, I thought there was no huge difference between the two, and I took the position that a little larger is better than a little smaller, and I went with the 460,000 BTUs.

NRT_Rob

If you have a 5,000 sq ft house

that means you were quoted boilers that were AVERAGING your heat load at 70 to 90 BTUs/sq ft.



If this house were not insulated, and it was pretty cold where you live, I might buy that.



If the house IS insulated, I've never seen an AVERAGE load over 30 BTUs/sq ft, which would mean this boiler would be 2.5 to 3 times too large.



The good news is radiators make great buffer units.



The bad news is, either your plumbers have no idea what they are doing, or you have an incredibly poor envelope and they were appropriately conservative.



if the boiler never runs more than ten minutes at a whack though, I would guess it's incredibly oversized. That would drop your efficiency quite a bit, especially if the boiler is installed in otherwise unheated space.

Dave Yates (GrandPAH)

run the numbers

Download this book and go to page 66. Measure your radiators and calculate the connected load EDR. Then you can determine if your boiler is as oversized as it sounds like from the description here.



Otherwise, it's a shot-in-the-dark & that just might be shooting yourself in the foot when sizing by the seat-of-your pants!



www.usboiler.burnham.com/PDF/htghelper.pdf 

Mark N

EDR

EDR stands for equivalent direct radiation. A steam rad emits 240 btus/hr for every sqft of EDR. There is a difference between a 460,000 btu boiler and a 340,000 btu boiler its a 120,000 btus. The bigger boiler will burn an extra 1.2 therms of gas per hour, every hour it runs. Over the life time of that boiler thats a lot of money. My house has 250 sqft of rads for every 1000 sqft. You have a 5000 sqft house so you might have 1000 plus sgft of rads.

icesailor

Normal Radiators:

What I'd like to see is a copy of the radiators and their EDR ratings per section. Like in my GAMA/IBR #250 advanced design guide. Or is it now in the new H-22 guide.

Inquiring minds (mine) are wondering.