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# Calculating Gas utility usage and cost for Steam Systems

Member, Email Confirmation Posts: 1
Would anyone know how to estimate the utility cost for gas usage based on a new gas fired steam boiler heating system in an existing building. The job is a retrofit/replacement. I have calculated that i will need a boiler with a steam Sq/ft capacity of 6499 with 2520 Gas Input at 80% efficiency. The boiler will run form 6 am through 8 pm during normal occupied hours.

The current steam system is a 1 pipe low pressure steam boiler that i want to run at 1.5 PSI (High) with a differential of 1 PSI with a subtractive differential. The boiler will cycle as needed throughout the day on cold days via local controls.

Assuming all local radiator and main line vents have been installed through out so venting air wont be an issue. Can i estimate my gas utility cost with the information above?

• Member Posts: 22,934
No. Sorry. The gas usage of the new boiler will probably be different from that of the old boiler -- but only in the amount the boiler itself differs in how efficient they are in converting gas coming it to heat used in the building.

Therefore, assuming no changes in usage (it's still in the same climate, occupancy the same, any process uses the same) the best place to start is also the simplest: You know the gross gas usage of the old system (you get that from the utilities bills). You know -- or can estimate -- the efficiency of the old boiler. That will allow you to figure the net heat sent to the building. Then you know the efficiency of the new boiler. That will let you calculate the gross gas usage from the net heat which is required.

You'll not get more accurate than that.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 8,576
If your interested in efficiency and economy, you would be advised not to have such an extreme temperature setback, as off for ten hours.
It would be best to set a lower constant temperature and let it run all the time, so the system doesn’t have to play catch up.
There are other changes you can make to make the system more efficient. Get some of the steam books from the store here for details.
Why did the old boiler fail?