Underfloor heating and PV solar are two of the smartest investments an Australian homeowner can make. When you combine them, each one makes the other more valuable.
Your solar panels generate electricity that would otherwise be exported to the grid at a low feed-in tariff. Your underfloor heating , either electric or hydronic, uses that electricity to warm your home at a low cost.
The result is whole-home comfort with a running cost that can drop to almost nothing on a good solar day.
This guide explains exactly how Comfort Heat electric and hydronic systems integrate with PV solar, how to schedule your system to maximise solar self-consumption, and what to expect from your running costs once both systems are working together.
Why Underfloor Heating and Solar Are a Natural Pairing
Most Australian heating systems and solar setups exist in parallel. The solar generates power during the day, the heating runs in the evening, and the two never really interact. Underfloor heating breaks that pattern in a useful way.
The reason is thermal mass. A concrete slab or a well insulated screed floor stores heat effectively. You can charge it during the middle of the day when your solar panels are generating at peak output and you have surplus electricity, and it will release that warmth slowly through the evening, when your family is home and when grid electricity is most expensive.
This is the single most important concept in solar-integrated underfloor heating: the floor is a battery. Not a lithium battery, but a thermal one.
For Australian homeowners on time of use tariffs, pre heating the slab during peak solar hours and letting it coast through the evening peak is one of the most effective energy management strategies available.
The floor acts as a battery. Charge it with solar during the day, let it release warmth into the evening. No lithium required.
How Electric Underfloor Heating Integrates with Solar
Electric underfloor heating is the simplest system to integrate with solar. The heating elements – whether Thin Heating Mats in bathrooms and kitchens or Slab Cable systems under larger floor areas – are pure electrical loads. They draw from whatever power source is available.
When your solar system is generating, it draws from your panels. When solar is not available, they draw from the grid. No special configuration is required.
What turns a basic electric system into a genuinely solar smart system is scheduling. The MWD5 Wi-Fi thermostat allows you to programme a 7-day heating schedule with up to four events per day.
Setting your primary heating window to align with your solar generation hours (typically 9am to 3pm for north-facing panels in Australian winter) means the bulk of your heating runs on solar rather than grid power.
Scheduling for Solar with the MWD5
Australian solar panels are most productive between 10am and 2pm, with the generation window extending from around 8am to 4pm in winter depending on roof pitch, orientation, and cloud cover. A practical solar-optimised schedule for an electric underfloor heating system running in a typical Australian home looks like this:
| Time Window | Purpose | Power Source |
|---|---|---|
| 6:00am – 8:00am | Morning warm-up before occupants leave | Grid (off-peak if available) |
| 9:00am – 3:00pm | Primary solar heating window – charges slab | Rooftop PV solar (surplus generation) |
| 3:00pm – 5:00pm | Top-up before evening – uses remaining solar | Solar fading to grid |
| 5:00pm – 9:00pm | Evening comfort – slab releases stored heat | Minimal grid draw needed |
Indicative schedule for a well-insulated home with a north-facing solar array. Adjust based on your generation profile and tariff.
The MWD5 thermostat also has a built-in Wi-Fi app so you can monitor and adjust the schedule remotely — useful when weather changes unexpectedly. For a full walkthrough of programming the MWD5, read our simple guide to turning on your MWD5 thermostat this winter.
Comfort Heat tip: Hydronic slab systems have the greatest thermal storage capacity of any Comfort Heat system. If you have an existing solar array or are planning to install one, an slab hydronic system is the best long term investment in solar-powered home comfort.
The Intaflo Heat Pump: Built for Solar
The Intaflo Series 3 heat pump is Comfort Heat’s recommended heat source for all hydronic underfloor heating systems.
It is an air to water inverter unit that produces around 4 units of heat for every 1 unit of electricity consumed — a COP (coefficient of performance) of 4 depending on ambient temperature and flow rate.
What this means for solar integration is significant. For every kilowatt of solar electricity the heat pump consumes, it delivers around 4 kilowatts of heating to the floor circuit. A 6.6kW rooftop solar system generating at 70% capacity during a typical winter day produces around 4.6kW — enough to run the Intaflo 9kW unit (designed for 40 to 100 square metres of floor area) while still powering the rest of the home.
| Intaflo Model | Ideal Floor Area | Nominal Power Input | COP | Solar System to Run on Solar Alone (approx.) |
|---|---|---|---|---|
| Intaflo 9kW Series 3 | 40–100 m² | ~2.2 kW | ~4.0 | 3–4 kW solar system |
| Intaflo 12kW Series 3 | 80–130 m² | ~3.0 kW | ~4.0 | 4–5 kW solar system |
| Intaflo 18kW Series 3 | 120–200 m² | ~4.5 kW | ~4.0 | 6.6 kW solar system |
| Intaflo 24kW Series 3 | 180–270 m² | ~6.0 kW | ~4.0 | 6.6–10 kW solar system |
| Intaflo 30kW Series 3 | 250–350 m² | ~7.5 kW | ~4.0 | 10 kW+ solar system |
COP figures at A6/W35 standard conditions. Solar system size is approximate and assumes the heat pump runs during peak solar generation hours only. Actual solar output varies by location, roof pitch, and panel orientation.
The Intaflo Series 3 range uses R32 refrigerant, which has a 60% lower global warming potential than previous refrigerants. It is rated A+++ for energy efficiency under European standards, the highest classification available, and carries inverter technology for smooth, variable-speed operation that reduces electricity consumption during partial-load conditions.
If you are moving away from gas and want to understand the full picture, read our guide to rethinking gas in your new home. The Intaflo heat pump is one of the key reasons the transition to an all-electric home is now genuinely viable for Australian homeowners.
How to Schedule Your System to Maximise Solar Self-Consumption
Scheduling is the most important lever you have for solar-integrated underfloor heating. The principles are the same for both electric and hydronic systems, though hydronic systems have more thermal storage and therefore more flexibility.
The Core Principle: Pre-Heat During Solar Hours
Australian rooftop solar is most productive between 9am and 3pm. For most homeowners, this is a period when the house is empty or has low occupancy. Rather than letting that solar generation flow into the grid at a low feed-in tariff, schedule your underfloor heating to run during this window. The floor absorbs the heat, stores it, and releases it gradually through the afternoon and evening.
Solar Generation Hours by State and Panel Orientation
| Panel Orientation | Peak Generation Window | Notes |
| North-facing | 10:00am – 2:00pm | Optimal for winter heating; maximum midday output |
| East-facing | 8:00am – 11:00am | Earlier morning generation; less useful for pre-heating |
| West-facing | 2:00pm – 5:00pm | Useful top-up generation in the afternoon |
| North + West combined | 9:00am – 4:00pm | Best profile for all-day pre-heating schedule |
Based on Australian winter solar generation profiles. Actual output varies by latitude, roof pitch, shading, and panel efficiency.
Insulation quality is the multiplier on all of this. A well-insulated slab retains heat far longer than a poorly insulated one, which means the pre-heating window can be shorter and the evening comfort window can be longer. Read our guide to the importance of insulation under a heated slab for the full technical picture.
Practical Scheduling for Hydronic Systems
For hydronic systems with the Intaflo heat pump, schedule the heat pump to run one or two cycles during the peak solar window, typically a 2 to 3-hour cycle from 10am to 1pm, and a top-up cycle from 1pm to 3pm if afternoon solar is available. The MWD5 thermostat on the hydronic circuit supports this schedule directly. Set the target water temperature for the floor circuit, and the heat pump will run until it is achieved, drawing from solar the entire time.
Running Cost Comparison: Grid vs Solar-Powered
The difference in running costs between grid-powered and solar-powered underfloor heating is substantial.
Here is how the numbers work for a 100m2 for winter. This is an guide only.
| System | Power Source | Approx. Annual Running Cost (Heating) |
| Electric underfloor – (slab) | Grid only | $2,800 |
| Electric underfloor (slab) | Solar (scheduled) | $1,500 |
| Hydronic + Intaflo heat pump | Grid only | $500 |
| Hydronic + Intaflo heat pump | Solar (6.6kW+ system, scheduled) | $20 |
| Hydronic + Intaflo heat pump | Solar + battery | Near $0 per year (battery covers evening) |
Figures are indicative, actual costs depend on tariff, insulation, climate zone, solar system size, and usage patterns.
For a detailed breakdown of running costs across all Comfort Heat system types, use the Comfort Heat Running Cost Calculator — enter your floor area, electricity tariff, and solar system size to see exactly what your heating will cost per day, per week, and over a full winter.
Adding a Battery: Does It Make Sense?
A home battery extends the value of solar integration for underfloor heating by storing surplus midday generation and making it available in the evening. Whether it makes financial sense depends on your tariff structure, solar system size, and how you use your heating.
For hydronic underfloor heating with a concrete slab, the slab itself provides substantial thermal storage, the equivalent of several kilowatt-hours of heat storage at no extra cost. In most cases, the slab’s thermal mass means a battery is not required to achieve evening comfort from a daytime solar heating cycle.
For electric underfloor heating in individual rooms such as bathrooms and bedrooms where the thermal mass is lower and the heating cycle is shorter, a battery is more relevant.
These rooms heat quickly and are typically used for short periods. The value of a battery in this scenario is required.
In these situations, a 10kWh battery can absorb excess midday solar generation and power the Intaflo heat pump through a top-up cycle at 6pm, entirely off stored solar energy.
Comfort Heat’s view: the slab is your first battery. Install a well-insulated in slab hydronic system, schedule it to heat on solar, and assess your grid top-up costs after one full winter before deciding whether a lithium battery adds sufficient further value for your household.
What You Need for a Solar-Integrated Underfloor Heating System
You do not need any special hardware to integrate a Comfort Heat system with rooftop PV solar.
All Comfort Heat thermostats and the Intaflo heat pump run on standard single or three-phase mains electricity. When solar is generating, the system draws from solar.
When solar is insufficient, it draws from the grid. The integration is automatic.
What you do need is:
- A programmable thermostat such as the MWD5, which allows you to set heating windows that align with your solar generation profile. A non-programmable thermostat won’t be able to take advantage of solar scheduling.
- A solar system of sufficient size. For electric room heating, talk to our inhouse expert on you heat load requirements. For hydorinc setups, see the Intaflo model table above for sizing guidance by floor area.
- A well-insulated floor. Insulation under the slab or screed is the most important factor in extending the heating window after the solar cycle ends. Read more in our guide to slab insulation for underfloor heating.
Knowledge of your solar generation profile. North-facing panels peak at midday; west-facing panels peak in the afternoon. Your MWD5 schedule should be tuned to your specific roof orientation. Our running cost calculator includes a solar offset estimator to help with this.
New Builds vs Retrofits
New Builds
New builds offer the most complete solar integration opportunity. The in-slab hydronic system is specified at the design stage, insulation is built in from the ground up, and the solar system can be sized to match the heat pump from the outset.
This is the combination we at Comfort Heat recommends most strongly for homeowners building in cool-climate states.
Read our full guide to installing energy-efficient underfloor heating in a new home for the complete specification process.
Renovations and Retrofits
For existing homes, electric underfloor heating during a renovation — particularly in bathrooms and kitchens with the Thin Heating Mat — is the most practical solar-integrated upgrade available.
The system sits within the tile adhesive layer, adds minimal floor height, and can be running on a solar-scheduled MWD5 thermostat from day one. Running costs for a bathroom heated on solar are typically less than $10 for an entire winter.
For larger whole-home retrofits, a hydronic in-screed system is possible in many existing homes, particularly during kitchen and living area renovations.
The team here at Comfort Heat has over 25 years of experience and will always a custom design layout that assesses whether your existing floor structure is suitable. Contact the team to discuss your specific renovation.
