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RME / Engineering Toolbox

Quick answers.Clear assumptions.

Boiler-room calculations for the number you need right now. Change any input and every result updates instantly.

ConvertAir + louversEnergy savingsFlow + pressureExpansion tanks
Heat + fuel

Input-to-output converter

01
Fuel input4,000,0004,000 MBH input
Estimated boiler output3,360MBH at selected efficiency
Boiler horsepower100.37BHP output rating
No. 2 fuel oil input28.57gallons/hr
Natural gas input4,000cubic feet/hr
Equivalent steam output3,463lb/hr from + at 212°F
Conversion assumptions
%
BTU/gal
BTU/ft³
Boiler HP is an output rating: 1 BHP = 33,475 BTU/hr output = 34.5 lb/hr steam. Required fuel input = rated output ÷ efficiency.
Combustion air

Opening + louver sizing

02
BTU/hr
%
inches
Required net free area1,000square inches
Gross louver area1,250square inches
At selected width24 × 53minimum nominal inches

The 80% default reflects the requested 20% louver allowance. Actual certified free area can vary substantially. Verify the appliance instructions, adopted code, duct configuration, local authority, and louver manufacturer’s data before design or installation.

Seasonal operating estimate

Boiler efficiency savings

03
MBH
%
%
%
hours
$/ therm
$cost

The $1.08/therm statewide planning default converts the June 2026 EIA Ohio commercial average of $11.22/Mcf at 10.37 therms per Mcf. Your actual delivered bill rate is the right number to use. Check current Ohio data ↗

Estimated seasonal savings$4,909
Fuel avoided4,545 therms
Fuel reduction11.4%
Simple paybackAdd project cost
Estimate holds delivered heat constant: new fuel = existing fuel × existing efficiency ÷ new efficiency.
Hydronics

Water flow

04
MBH
°F
factor
Required flow100.0GPM
FormulaQ ÷ 500ΔTadjust factor for fluid properties
Standard water calculation uses BTU/hr = 500 × GPM × ΔT.
Pressure

Head converter

05
ft / PSI
Pressure10.00PSI
Water head23.10feet
Metric pressure68.95kPa
Default conversion is for water near standard conditions; fluid density changes the relationship.
Hydronic expansion

Expansion tank estimator

06
Start with connected load

Estimate a new system

MBH
%
gal / output MBH
°F
°F
PSIG
PSIG
Estimated system water924gallons
Water expansion34.6gallons acceptance required
Minimum diaphragm tank106gallons total volume
Pressure acceptance factor32.7%at entered pressures

The system-volume presets are planning factors derived from Bell & Gossett’s average component-volume table. Enter calculated system gallons when available. Maximum operating pressure is normally kept below the relief setting. View engineering method ↗

Existing steel tank

Replace a gravity / compression tank

gallons
PSIG
PSIG
Minimum diaphragm tank volume33.0gallons
Minimum acceptance volume13.3gallons
Replacement specification33 gal total / 13.3 gal acceptanceSelect the next available bladder or diaphragm tank that meets or exceeds both figures, then set its precharge to the cold fill pressure before connecting it.

This conversion uses the published pressure relationship between an atmospheric steel compression tank and a precharged diaphragm tank. Confirm the old tank’s actual volume, operating pressures, tank location, relief setting, and the selected manufacturer’s acceptance rating. View replacement method ↗

Steam systems

Feedwater receiver

06
minutes
Steam evaporation2.06gallons per minute
Required net storage20.6usable gallons
Typical gross receiver42gallons — select next size up
Uses 1 BHP = 33,475 BTU/hr output = 0.069 GPM evaporation. Gross receiver assumes 50% usable volume. Size for every boiler that can fire together and confirm the selected manufacturer’s net-storage rating.