Radiant Floor Heating Cost Calculator

Related Calculators

Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

Radiant floor heating: A heating system that warms the floor surface so heat moves upward into the room.

Hydronic: Warm-water floor heat, where heated water moves through tubing under the floor.

Heated floor area: The square footage that has radiant heat installed, not necessarily the whole room or house.

Installed cost range: The low and high planning estimate for buying and installing the system.

Heat used while on: The average heat power used during active heating, measured in watts per square foot.

Kilowatt-hour (kWh): A unit of energy used on electric bills.

Therm: A natural gas energy unit used by some gas bills.

First-year cost gap: electric minus hydronic: Electric first-year total minus hydronic first-year total; a negative value means electric is lower in the first year.

Mistake: Entering the whole house in Heated floor area when only one room has radiant heat.
Fix: Use only the square footage that will actually be heated.

Mistake: Leaving Electricity price blank or typing a dollar rate when the label asks for cents per kWh.
Fix: Enter cents, such as 16 for $0.16 per kWh.

Mistake: Reversing Electric installed low price and Electric installed high price.
Fix: Make Electric installed high price greater than or equal to Electric installed low price.

Mistake: Entering 150 in Hydronic heater efficiency because a high-efficiency claim sounds better than 100 percent.
Fix: Use a value greater than 0 and no more than 100, such as 90 for 90 percent.

Mistake: Using Hydronic fuel price from a propane gallon or oil gallon bill without converting it to $ per therm.
Fix: Convert your fuel cost to dollars per therm before entering it, or keep the result as a rough comparison only.

Mistake: Reading First-year cost gap: electric minus hydronic as a positive savings number every time.
Fix: Positive means electric costs more in year one; negative means electric costs less in year one.

• This is a planning estimate, not a contractor bid. Labor, demolition, subfloor repair, controls, permits, and local code requirements can change the real price.
• No ZIP lookup is used. Local price adjustment is a user-entered factor, so replace the default installed prices with local quotes when possible.
• The running-cost model uses average Heat used while on and Heated time. It does not calculate heat loss from insulation, outdoor temperature, ceiling height, window area, or thermostat schedule.
• Hydronic running cost assumes the heat source fuel is priced in $ per therm and uses the entered Hydronic heater efficiency.
• Electric running cost treats electric floor heat as resistance heat for this comparison.
• Floor covering and Install setting multipliers are simple planning factors. Actual floor prep and heat-transfer limits may require a different design.
• Monthly running cost is an average annual month. Winter bills can be higher and shoulder-season bills can be lower.

Installed cost range

The calculator estimates electric and hydronic installed costs separately. It starts with Heated floor area and the entered low and high installed prices per square foot. It then applies the Install setting multiplier, Floor covering multiplier, Local price adjustment, and Extra fixed costs.

install_multiplier = 1.00 for new floor or open subfloor; 1.20 for existing finished floor; 1.50 for concrete slab or major rework

floor_multiplier = 1.00 for tile or stone; 1.05 for vinyl or laminate; 1.10 for engineered wood; 1.15 for carpet

local_factor = Local price adjustment / 100

installed_low = Heated floor area * low price per sq ft * install_multiplier * floor_multiplier * local_factor + Extra fixed costs

installed_high = Heated floor area * high price per sq ft * install_multiplier * floor_multiplier * local_factor + Extra fixed costs

installed_midpoint = (installed_low + installed_high) / 2

Running cost

Annual useful heat is estimated from area, heat power, daily heated time, and 365 days. Electric running cost uses the entered Electricity price. Hydronic running cost converts useful heat to fuel therms after applying Hydronic heater efficiency. The therm conversion uses 100,000 Btu per therm and 3,412.141633 Btu per kWh, so 1 therm is about 29.30011111 kWh.

thermal_kwh_per_year = Heated floor area * Heat used while on / 1000 * Heated time * 365

electric_annual_run_cost = thermal_kwh_per_year * Electricity price / 100

electric_monthly_run_cost = electric_annual_run_cost / 12

efficiency_decimal = Hydronic heater efficiency / 100

hydronic_annual_run_cost = thermal_kwh_per_year / efficiency_decimal / 29.30011111 * Hydronic fuel price

hydronic_monthly_run_cost = hydronic_annual_run_cost / 12

First-year comparison

The first-year totals use the midpoint installed cost plus one year of running cost. The gap keeps its sign because negative values are useful.

electric_first_year_total = electric_installed_midpoint + electric_annual_run_cost

hydronic_first_year_total = hydronic_installed_midpoint + hydronic_annual_run_cost

first_year_cost_gap = electric_first_year_total - hydronic_first_year_total

A positive gap means electric is estimated to cost more in the first year. A negative gap means electric is estimated to cost less in the first year.

Worked example

For 150 sq ft, 4 heated hours per day, 16 cents per kWh, 10 watts per sq ft, $1.50 per therm, 90 percent hydronic efficiency, and the default installed prices, the calculator gets these values:

thermal_kwh_per_year = 150 * 10 / 1000 * 4 * 365 = 2190 kWh

electric_annual_run_cost = 2190 * 16 / 100 = $350.40

hydronic_annual_run_cost = 2190 / 0.90 / 29.30011111 * 1.50 = $124.57

electric_first_year_total = $2400 + $350.40 = $2750.40

hydronic_first_year_total = $4500 + $124.57 = $4624.57

first_year_cost_gap = $2750.40 - $4624.57 = -$1874.17