Floor Heating Operating Cost Calculator - Technical Specification

Overview

The WarmlyYours Operating Cost Calculator estimates the daily, monthly, and annual electricity costs for running radiant floor heating systems. The calculator has two implementations:

1. Public Calculator - A simplified client-side calculation for quick estimates
2. Advanced Calculator - A backend service that accounts for monthly temperature variations and thermostat schedules

---

1. Public Calculator (Frontend)

Location

• ViewComponent: app/components/www/floor_heating_calculator_component.rb
• ViewComponent: app/components/www/snow_melting_calculator_component.rb
• Stimulus controller: app/javascript/controllers/floor_heating_calculator_controller.js
• Stimulus controller: app/javascript/controllers/snow_melting_calculator_controller.js

Formula

Cost (cents/day) = kWh_rate × sqft × (hours / 2.3) × wattage / 1000

Variables

Variable	Description	Default	Source
kWh_rate	Electricity rate (cents/kWh)	12-13¢	Fetched from /api/v1/locations/by_postal_code/:zip
sqft	Heated square footage	35 sq ft	User input
hours	Daily operating hours	8 hours	User input (slider)
wattage	Watts per square foot	15 W/sq ft	Based on selected heating system

Duty Cycle Factor

The divisor 2.3 represents a duty cycle factor, accounting for the fact that floor heating systems cycle on and off rather than running continuously. This equates to approximately 43% runtime (1/2.3 ≈ 0.43).

Wattage by Product

Heating System	Watts/sq ft
TempZone Flex Roll	15
TempZone Easy Mat	15
TempZone Cable (3” spacing)	14.8
TempZone Cable (4” spacing)	11.1
TempZone Cable (5” spacing)	8.9
Environ Flex Roll	12
Environ Easy Mat	12
Slab Heat Mat	20

Example Calculation

For a 50 sq ft bathroom with TempZone Flex Roll, 8 hours/day use, at 12¢/kWh:

Cost = 12 × 50 × (8 / 2.3) × 15 / 1000
     = 12 × 50 × 3.48 × 15 / 1000
     = 31,320 / 1000
     = 31.32 cents/day (~$0.31/day)

---

2. Advanced Calculator (Backend)

Location

• app/services/room_configuration/operating_costs_calculator.rb
• config/initializers/room_configuration_constant.rb
• app/models/room_configuration.rb

Overview

The advanced calculator computes monthly costs by:

1. Fetching local average monthly temperatures by postal code
2. Calculating operating hours based on temperature differential
3. Applying weekday/weekend thermostat schedules
4. Multiplying by system wattage and electricity rate

Primary Formula

monthly_cost = operating_hours × kilowatts × electricity_rate

Where:

operating_hours = (comfort_hours × comfort_factor) + (economy_hours × economy_factor)

Temperature-Based Operating Factor

The system calculates how much heating is needed based on the temperature differential between desired indoor temperature and actual outdoor temperature:

# Comfort mode factor
tdiff_comfort = comfort_temp - outdoor_temp
tdiff_comfort = 0 if tdiff_comfort < 0            # No heating needed if warmer outside
tdiff_comfort = comfort_temp if tdiff_comfort > comfort_temp  # Cap at max
factor_comfort = tdiff_comfort / comfort_temp

# Economy mode factor
tdiff_economy = economy_temp - outdoor_temp
tdiff_economy = 0 if tdiff_economy < 0
tdiff_economy = economy_temp if tdiff_economy > economy_temp
factor_economy = tdiff_economy / economy_temp

Interpretation:

• When outdoor temp equals indoor setpoint → factor = 0 (no heating needed)
• When outdoor temp is very cold → factor approaches 1.0 (maximum heating)
• Linear interpolation between these extremes

Constants

Defined in config/initializers/room_configuration_constant.rb:

module RoomConfigurationConstants
  AVG_DAYS_PER_MONTH = {
    week_day: 21.75,
    week_end_day: 8.69
  }

  HOURS_OF_OPERATION_PER_DAY = {
    comfort: { week_day: 9.0, week_end_day: 15.0 },
    economy: { week_day: 15.0, week_end_day: 9.0 }
  }

  AVERAGE_HOURS = {
    avg_num_hrs_per_month: 730.56,
    avg_num_comfort_hrs_per_month: 332.605,  # ~11 hrs/day
    avg_num_economy_hrs_per_month: 397.955   # ~13 hrs/day
  }
end

Temperature Presets

Defined in app/models/room_configuration.rb:

TEMPERATURE_OPTIONS = [
  ['Low', 60.0],      # Economy setting
  ['Average', 68.0],  # Comfort setting (default)
  ['Warm', 72.0],
  ['Hot', 80.0]
]

Kilowatt Calculation

def calculate_total_watts
  heating_elements.sum { |he| he.quantity * he.item.watts.to_f }
end

def calculate_total_kilowatts
  calculate_total_watts / 1000.0
end

Data Sources

Data	Source	Model
Average monthly temperatures	By postal code	AverageMonthlyTemperature
Electricity rates	By postal code	ElectricityRate
Heating element wattage	Product catalog	Item

Electricity Rate Philosophy (Updated December 2025)

For provinces/states with tiered pricing structures, we use the marginal rate (Tier 2 / Step 2) rather than the blended average. This is because:

1. Floor heating is additive consumption - When customers add floor heating, they’re adding NEW load on top of existing usage
2. Base usage consumes lower tiers - A household’s existing consumption (lights, appliances, HVAC) typically uses up the cheaper Tier 1 allowance
3. Additional heating pays the higher rate - The floor heating electricity is billed at the marginal (higher) rate

Example - Quebec (Hydro-Québec Rate D):

• Tier 1: ~6.9¢/kWh (first 40 kWh/day)
• Tier 2: ~10.7¢/kWh (above 40 kWh/day) ← We use this rate
• Using the blended average (7.8¢) would underestimate heating costs by ~27%

Provinces with tiered pricing:

• Quebec: Tier 2 rate (10.7¢) used instead of blended average
• BC: Step 2 rate (14.08¢) used instead of Step 1 (11.72¢)
• Ontario: Mid-peak TOU rate used as representative for heating load

---

3. Heat Loss Integration

When detailed room information is available, the calculator uses heat loss calculations for more accurate estimates.

Trigger Conditions

Heat loss calculation is used when:

• allow_heat_loss_calculation? returns true
• can_calculate_heat_loss? returns true
• Room has an indoor floor type

Heat Loss Factors

The detailed calculation accounts for:

• Room insulation (walls, ceiling, floor)
• Window and door openings (U-values)
• Infiltration/air sealing quality
• Room dimensions and orientation

BTU Conversion

BTU_PER_HOUR_PER_WATT = 3.4121416

Located in app/models/heat_lossable_constants.rb

Monthly kWh from Heat Loss

def self.get_monthly_operation_kwh(hl_avg_comfort, hl_avg_economy)
  monthly_kwh = 0.0
  [:week_day, :week_end_day].each do |days_type|
    { comfort: hl_avg_comfort, economy: hl_avg_economy }.each do |mode, hl|
      monthly_kwh += AVG_DAYS_PER_MONTH[days_type] *
                     HOURS_OF_OPERATION_PER_DAY[mode][days_type] *
                     (hl / BTU_PER_HOUR_PER_WATT) / 1000.0
    end
  end
  monthly_kwh
end

---

4. API Endpoints

Get Electricity Rate by Postal Code

GET /api/v1/locations/by_postal_code/:postal_code

Response:

{
  "status": "ok",
  "average_rate": 0.12
}

Get Electricity Rate by Coordinates

GET /api/v1/locations/by_lat_lng/?lat=:latitude&lng=:longitude

---

5. Output Format

Backend Calculator Response

{
  status: 'ok',
  operating_cost_by_month: [jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec],
  operating_cost_annual: 125.50,
  operating_cost_by_month_average: 10.46,
  operating_cost_by_coldest_month: 28.75,
  message: "assuming default SmartStat settings, yielding average operation of
            4.2 hours per day annually, and coldest month operation of
            8.1 hours per day, based on average monthly temperatures and
            electricity rates in your area."
}

Frontend Display

The frontend converts the cost to display:

• Per day: ${(cost / 100).toFixed(2)}
• Per month: ${((cost / 100) * 30).toFixed(2)}
• Per year: ${((cost / 100) * 365).toFixed(2)}

---

6. Quick Reference: Cost Estimation

Typical Operating Costs

Based on the website copy (app/views/pages/floor-heating.html.erb):

Electric floor heating typically costs $0.07–$0.36 per hour. For a standard bathroom (~40 sq. ft.) running a few hours daily: $17–$29 per month.

Factors Affecting Cost

1. Room size — Larger rooms = higher costs
2. Flooring material — Tile/stone transfer heat efficiently; carpet/wood may require more energy
3. Daily usage — 2 hours vs 6 hours makes a significant difference
4. Electricity rates — Local kWh pricing directly impacts costs

---

7. File References

File	Purpose
app/components/www/floor_heating_calculator_component.rb	Floor heating calculator ViewComponent
app/components/www/snow_melting_calculator_component.rb	Snow melting calculator ViewComponent
app/javascript/controllers/floor_heating_calculator_controller.js	Stimulus controller for floor heating
app/javascript/controllers/snow_melting_calculator_controller.js	Stimulus controller for snow melting
app/services/room_configuration/operating_costs_calculator.rb	Backend calculator service
config/initializers/room_configuration_constant.rb	Constants for hours/days
app/models/room_configuration.rb	Temperature options, wattage tables
app/models/heat_lossable_constants.rb	BTU conversion constant
app/views/pages/floor-heating/cost-calculator.html.erb	Public calculator page