Electric or gas hot water heating system

Gregory Rollins

I'm in the prosses of installing a hot water boiler for a new house that has 1300 sf. The baseboard req.19,034 Btu for the 1st fl and 8,653 Btu 2nd fl and 25,255 Btu for the basement (this will be radiation type in concret) total 52,853Btu I,ve looked at alot of systems and one is a LP gas boiler direct vent type sealed combustion rated at 50,000 btu D.O.E. 84% Eff. Capacity.The other is an electric boiler at 55,000 btu D.O.E. cap. (16Kw @240v). What i want to know is will the electric be more eff. then the gas. The rate for electric is .04-.09 @ Kwh.The LP gas is $2.45 @ gal.Also what is the NET I=B=R mean. I know you want to size the boiler by the output Btu and the baseboard Req.Also is it better for a boiler to run longer than short time cycle.

Jim Keyes

NET I=B=R definition

The Hydronics Institute Division of GAMA site lists a whole lot of ratings and tells us that I=B=R is derived from the old Institute of Boiler and Radiation Manufacturers.
The ratings are there to allow us to "read from the same sheet of music" when we are trying to design a radiant/hydronic system. By harmonizing the ratings and putting them in one place, they have done the industry a huge service!
Look here for more: http://www.gamanet.org/

Jim Keyes

Relative efficiency

In theory, electric heating is 100% efficient. LP gas is rarely over 84%. Both ratings are input values in a lot of literature. Look for output values or ask the manufacturer for them.
Don't fret efficiency as much as operating cost, though.
One THERM of natural gas or one GALLON of LP gas each contain about 100,000 BTUH's of heat value. One kwh of electricity is 3413BTUH. So 29.3KWH = 1 THERM. At $0.09/KWH, 1 THERM EQUIVALENT = $2.64
However, since the gas appliance is only 84% efficient, it takes ~1.19 THERMS to get 100K BTUH delivered to the water and that costs $2.92.
I live in North Arkansas, where much of the feedwater is chewable and maintenance of residential equipment gets short shrift, so I try to install electric appliances based on operating cost and on life cycle maintenance costs.
Where there is an industrial process demand such as the 200KW metal prep line we are doing now, you have to really look at operating costs carefully. In the summer, we can typically buy LP gas for $0.45/gal [5000 gallons!] and coast through the winter on stored fuel. If you can do that, electricity just doesn't compete.

Jim Keyes

is it better for a boiler to run longer than short time cycle

It depends on the amount of heat required to maintain comfort. When it is colder than a stepmother's kiss outside, it MUST run longer, since the input rating is pretty close to the output required from the radiators. The Dead Man I used to work for designed for 5% excess output at coldest design point. I'm sure that some of his systems were sort of cold when they were old and dirty or full of air, but he kept a lot of Oregon warm!
In an ideal world, the boiler should fire continuously at coldest design point, with linear decrease in firing time as outside air warms. In the real world, no one wants that and we spend a lot of money on insulation, infiltration control and such things so the boiler can "rest between jobs". It is really the same, though. Output = Firing rate x Time.

jeff_51

gas all the way

I've never known an electric boiler that could compete with gas over the long haul. Those immersion coils always will have to be replaced at some point, usually around ten to fifteen years and that is usually some kind of job. Am also assuming you would go with dhw off the boiler. As the prvious post said, if you are on lp, get a tank big enough to run you through the winter so you don't have to buy that late winter fill, than you can really save. And yes, the longer the run the more efficient.