You can get the number here for your own location Lastly, I went and snagged my degree day data which translates to the number of heating days between October and April that number is 7566. I heat with Natural gas so I get 100,000 BTU per therm of gas. For reference here is the BTU content of fuel for the most common fuel types Based off of a 90 degree rise in water from ‘city water temp’ to ‘heated water temp’, an input rating of 36,000 BTUS and the gallons per hour recovery rate of 30.5 ( both numbers are on the side of your water heater ) the AFUE of my water heater is 63.3% ( calculate your own with this tool )Īnother critical element is the BTU’s you get from the fuel you get. The formula is as follows ĮFU = (Heating Load x 24 x DD x CF) / (AFUE x Q x DTD)Įstimated Fuel Usage = ( Heating load X 24 x Heating Degree Days X Heating Degree Days Fuel Correction Factor ) / ( AFUE X BTU Content of Fuel X The Design Temp )Īs noted earlier I am heating with a water heater currently so I needed to get the AFUE of it with some math. Now that I have this information we can use a slick little formula to calculate the estimated fuel usage and from there I can calculate my cost to heat it based off local fuel rates. Using some free software, I was able to calculate my heating load to be 10,400 BTUS for the area in my home being heated by radiant infloor. To figure out the cost of operation, my first step was to do a heat loss / heat gain calculation. NOTE: Although I am sharing the math on how I do the calculations I will move quickly so if you have questions or if I am not overly clear on the math leave me a comment So if you do not know how to do it the right way, don’t! Call an expert! Its worth noting that hooking radiant infloor up directly to your domestic hot water heater can make you sick, damage your water heater and just plain cause you grief. A typical boiler install can easily run you $5-$9k depending on what boiler you choose so using my water heater to heat the small zone of radiant in my home made sense. The only reason I am doing it currently is because my heating load is so small and I could not afford to install a boiler at the time. Right off the bat let me say I do not encourage in any way shape or form running radiant in floor off a water heater. I am looking to upgrade my radiant heating system from a water heater to a boiler and I wanted to get a rough idea on the estimated fuel usage so I could narrow in on how much if any money I would save from this upgrade.
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