lp fuel comsumption

kevin

I have a job that I installed radiant floor heat in a slab.Three 180' loops,1/2" pex, heat loss approx.18,000btu. the area is 640 sq. ft.,r13 in 2x4walls,2" styrofoam in slab, A 008 runs the water around from a 40 gallon water heater (used as space heating only,NOT an open system)Heater is approx 36,000 btu.The room is used as a workshop for a contractor friend of mine.
He got the fist bill for the LP and was a bit alarmed at the amount of gas used, as was I. It works out to about to be a bout 3 1/2 gallons a day or about $180.00 for the month. This sounds high to me. The temps here in New Hampshire have been is the 20's and the occational dip to the single digits.
Does this seem high to you guys? Other than the usual caulking and adding insulation to the attic area what can I do to add efficiency to the system?.
Thank, kpc PS -appy new year!

Gary Fereday

That is about

13141.666 btu's per hour constantly. 0ver 24 hours. Close to what you calculated for the job, 13141.6 / 18000 = 73% efficientcie. Not bad. Insulation and infiltration would be best accomplished first before a new heating unit. good luck
bigugh

Dave Yates (PAH)

seems normal at low temps

91,500 Btu per gallon of propane

18,000 Btu heat loss (design day)

18,000 x 24 hours = 432,000

Efficiency of appliance??? Assuming it's 90%. 91,500 x .90 = 82,350 net Btu per gallon. At 70% that's 64,050.

432,000 divided by 82,350 = 5.25 GPD of propane on a design day & 6.74 GPD @ 70%.


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hr

A couple more thoughts

You mentioned this is workshop space. Does the space have an overhead garage door? These are terrible for infiltration leaks, even the insulated type. Which would run up fuel consumption quite a bit.

Is the water heater located in the same space? Combustion air openings for that size water heater burner, in a small square footage room, may be your biggest heat loss.

Tighten the space up a much as possible, but be careful about combustion air if the heater is located in the same space. And you need some fresh air to stay alive, of course

If it were me, I would look into a sealed combustion heater. A small modulating, condensing heater would be great. Waiting patiently for the 50,000 Munchkin for this application.

With a conventional water heater perhaps 25 cents of every fuel dollar goes up the flue pipe. With a 90% plus unit that looks much better.

The heat loss of the space drives the fuel costs, but using the most efficient heater will also make a difference. Wish I could heat my shop on 3-1/2 gallons a day!!

Sounds like a little more pump than you need also. Could save some electrical energy costs there 3-1/2 gallons X 30 days = 105 gallons. $180 per month? Sounds like expensive LP in your area. Currently I pay .89 per gallon. That would be $93.45 per month.

hot rod

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kevin

Thanks guys...

Propane here in seacoast NH is not cheap. He is paying $1.89 / gal. This shop has two french doors and three windows.Pretty tight there.
It was a budget job and the water heater is brand new.It is in the shop area and is one of the Flame Guard type by American Water Htr.
As to the 008, the Wirsbo program suggested a 008 for the loop lengths Three loops(204',201'& 183') A 007 doesn't quite make it ,I think. But I can be wrong about these things.
I will have him add more to the attic,and turn the temp down to 55-60*.

JackFre

Slab edge insulation

Did you insulate the perimeter of the slab? If not, I would do that first (come spring anyway). If you look at a radiant slab infra-red display with and w/o edge insulation you will be amazed at the difference.

steve gates

I'd go with the

oo7 or a 15-42 3speed.Look at the books Pumps curves and see why.