Recommendations
Compares different space heating systems (underfloor, wall, radiators, forced air - ducted & ductless) and provides recommendations for optimal comfort and efficiency considering property size.
You’re on your way to an optimal heating system! So far, we’ve talked about the key characteristics of your property. Now, let’s dive into the different ways you can actually deliver that heat to your living spaces – the space heating subsystems. Choosing the right system is crucial for achieving both comfort and efficiency. Are you tired of cold floors in the winter? Do some rooms feel stuffy while others are freezing? The right space heating system can make all the difference! And if you ever get stuck or need more information, remember our expert-level support is always available.
Why Space Heating Matters
The way heat is distributed throughout your home significantly impacts your comfort, your energy bills, and even the lifespan of your heating equipment. A well-chosen system will:
Maximize Comfort
Provide even, consistent warmth without drafts or cold spots.
Minimize Energy Waste
Efficiently transfer heat to the living spaces, reducing energy consumption.
Improve Indoor Air Quality
Minimize the circulation of dust and allergens (compared to forced air).
Protect Your Investment
Operate within optimal parameters, potentially extending the life of your heating equipment.
Choosing the wrong system, on the other hand, can lead to discomfort, high energy bills, and even potential health problems. This section helps you understand the options and make an informed decision.
Space Heating Subsystems
Operating Principles of Space Heating Subsystems
Let us go through the operation principles for the following common heating systems. We’re focusing on water-based (hydronic) versions of underfloor, wall, and radiator heating, as these are best suited for integration with heat pumps, solar collectors, and the OptiHeatX hybrid approach. Electric versions simply don’t offer the same flexibility or efficiency potential.
Forced Air Heating (Ductless Mini-Split)
In ductless systems (like mini-splits) individual units mounted on walls or ceilings heat (or cool) and circulate the air directly within the specific premise or zone they serve. Primarily relies on convection.
Forced Air Heating (Central/Ducted)
In central, ducted systems, air is heated usually by a furnace (using fuel or electricity) or air handler (that distributes heat generated by heat pump coils or backup electric heat strips) and then blown through ducts and out vents (diffusers) into your rooms. Primarily relies on convection.
Radiator Heating (Hydronic)
Hot water circulates through radiators. They heat the air around them through convection, and that hot air rises, creating circulation. They also emit some radiant heat. Can be high-temp or low-temp design.
Underfloor Heating (Hydronic)
Warm water (low temperature) flows through pipes embedded in the floor, primarily radiating heat upwards evenly across the entire floor surface.
Wall Heating (Hydronic)
Similar to underfloor heating, but the warm water pipes are embedded in the walls, radiating heat into the room.
Remember, only hybrid heating systems (ones that can use multiple types of heat sources, like heat pumps, solar, boilers) coupled with appropriate space heating subsystems can give you complete resilience and maximize efficiency!
In this chapter, we’ll check each of these, so you can figure out what’s best for your situation. Our goal? To help you choose the system that delivers both optimal performance and comfort for your well-insulated building, considering Small (S <75m²), Medium (M 75-150m²), and Large (L >150m²) properties. We’ll look at two flavors of water-based radiator heating: high-temperature and low-temperature. We’ll consider these systems both for new construction and renovations.
Characteristics of Space Heating Subsystems
Okay, let’s get down to business. We’re going to compare these systems across a whole bunch of characteristics:
Heat distribution uniformity
How evenly the heat spreads throughout the room.
Thermal comfort
How comfortable the heating method feels (e.g., radiant vs. convective, drafts).
Humidity comfort
How the system affects indoor humidity levels.
Bacteriological safety
Potential for harboring or spreading bacteria/mold.
Noise comfort
Operational noise level of the system.
Appearance
How visible the system components are within the living space.
Room usability comfort
How much the system interferes with furniture placement and room usage.
Compatibility with cooling
Ability of the system to be used effectively for cooling.
Risk of window condensation
The likelihood of condensation forming on windows, especially in cold weather.
Risk of moisture in corners/enclosed areas
Potential for dampness in poorly circulated areas.
Dust and allergen distribution
How much the system circulates airborne particles.
Void formation
Creation of hidden empty spaces (behind false ceilings, etc.) that can harbor pests.
Reduction of useful room height
How much ceiling height is lost due to system components (e.g., ducts, screed).
Reduction of useful room area
How much floor space is lost due to system components (e.g., radiators, plaster).
Material restrictions
Requirements or limitations on finishing materials (flooring, wall coverings).
Installation cost
Relative cost of labor for installation.
Materials and equipment cost
Relative cost of the necessary parts (excluding boiler room).
Maintenance complexity
Difficulty and frequency of required maintenance.
Efficiency
Overall energy efficiency of heat delivery (excluding source generation).
Installation simplicity
Ease of installation for typical scenarios.
Service life
Expected lifespan of the system components.
Thermal inertia
How well the system holds heat or how quickly it responds to temperature changes.
Window Condensation Risk: Increases as outdoor temperatures drop. It is especially promoted by single-pane windows, poorly insulated windows, and lack of ventilation leading to increased air humidity.
Thermal inertia — also known as the inverse of response speed — is the time it takes for the room air temperature to respond to heat flow in the heating system. The greater the thermal mass of the heated property, the slower it cools down and has higher inertia — and vice versa.
Installation Specifics for New Construction and Renovation
New Construction
Building from scratch offers maximum freedom to integrate any system optimally: design ideal duct paths, ensure structural support for radiators, allocate correct floor height for underfloor heating, or plan wall heating around wiring.
Renovation
Working with an existing building introduces constraints: limited space for ducts, existing structural limits for radiators, existing floor/ceiling heights impacting underfloor options, and potential conflicts between wall heating pipes and existing wiring requiring rerouting.
Drawbacks of Space Heating Subsystems
After looking at all those characteristics, here’s a summary of the key drawbacks or limitations for each system, noting how they can vary with property size (S <75m², M 75-150m², L >150m²).
(For the full comparison table with detailed ratings, see: Detailed Analysis of Characteristics)
Ductless Air Heating (Mini-Split) Drawbacks
Summary:
S(2🔴 14🟡) M/L(9🔴 7🟡)
🔴 Humidity comfort
🔴 Thermal inertia
S🟡 M🔴 L🔴 Appearance: More units = worse aesthetics
S🟡 M🔴 L🔴 Space usage comfort: More units = more placement constraints
S🟡 M🔴 L🔴 Installation simplicity: Multi-zone adds significant complexity
S🟡 M🔴 L🔴 Installation cost: Multi-zone escalates cost
S🟡 M🔴 L🔴 Materials and equipment cost: Multi-zone escalates cost
S🟡 M🔴 L🔴 Maintenance complexity: More units = more filters/drains
S🟡 M🔴 L🔴 Heat distribution uniformity: Harder in large/complex rooms
🟡 Thermal comfort: Drafts near unit
🟡 Risk of window condensation
🟡 Dust and allergen spread: Moves room air
🟡 Bacteriological safety: Indoor unit needs cleaning
🟡 Risk of moisture in corners and enclosed wall areas
🟡 Noise comfort: Indoor fan noise
🟡 Service life: 15-20 years
Central Ducted Forced Air Drawbacks
Summary:
S/M(12🔴 7🟡) L(14🔴 5🟡) without humidifier
S/M(11🔴 7🟡) L(13🔴 5🟡) with humidifier (but with added cost & complexity)
🔴 Dust and allergen spread: Duct system circulation
🔴 Bacteriological safety: Ducts can harbor growth
🔴 Noise comfort: System noise, air rush
🔴 Appearance: Without false ceiling - also air ducts visible
🔴 Reduction in useful room height: Requires thick air ducts
🔴 Void formation: Extensive voids for ducts
🔴 Installation simplicity: Requires ductwork
🔴 Installation cost:
🔴 Materials and equipment cost: Even without boiler room elements
🔴 Maintenance complexity: Requires regular filter and air duct maintenance
🔴 Thermal inertia
🔴/🟢 Humidity comfort: 🔴 Without air humidifier in system 🟢 With humidifier (added cost/complexity)
S🟡 M🟡 L🔴 Heat distribution uniformity: Difficulty balancing large duct systems
S🟡 M🟡 L🔴 Efficiency: Duct losses impact larger systems
🟡 Thermal comfort: Can create drafts
🟡 Risk of moisture in corners and enclosed wall areas
🟡 Risk of window condensation
🟡 Service life: 15-20 years
🟡 Material restrictions: False ceiling to hide ducts
Radiator Heating - High Temperature Drawbacks
Summary:
6🔴 1🟠 7🟡 with hidden piping
7🔴 1🟠 6🟡 with exposed piping
🔴 Heat distribution uniformity: Creates local heat zones. Cold zones, overheating near radiators.
🔴 Humidity comfort: Air dehumidification occurs. Convection flows worsen the problem.
🔴 Risk of window condensation: Especially with too high radiator temperatures
🔴 Risk of moisture in corners and enclosed wall areas: Especially with poor air circulation
🔴 Thermal inertia
🔴 Cooling compatibility
🟡/🔴 Appearance: Radiators visible 🔴 with exposed piping, pipes also visible
🟠 Reduction in useful room area: Yes
🟡 Efficiency
🟡 Thermal comfort: Has convection flow issues
🟡 Dust and allergen spread
🟡 Bacteriological safety
🟡 Materials and equipment cost
🟡 Maintenance complexity: Regular cleaning of radiators and exposed pipes required
Radiator Heating - Low Temperature Drawbacks
Summary:
4🔴 1🟠 5🟡
🔴 Appearance: Large radiators, worse impact on large walls
🔴 Space usage comfort: Significant impact, scales with size
🔴 Materials and equipment cost: Radiator cost scales massively
🔴 Maintenance complexity: Large radiators
🟠 Cooling compatibility¹: High condensation risk
🟡 Heat distribution uniformity: But if there are few radiators, floor area can be cold.
🟡 Humidity comfort
🟡 Risk of window condensation
🟡 Risk of moisture in corners and enclosed wall areas: Especially with poor air circulation
🟡 Thermal inertia
Underfloor Heating (Hydronic) Drawbacks
Summary:
1🔴 5🟡 for new construction
2🔴 5🟡 – 3🔴 3-4🟡 for renovation
🔴 Materials and equipment cost
🟡/🔴 Reduction in useful room height: 🟡 for new construction and renovation when screed required — By 5-7+ cm (insulation 3+ cm and 2-4+ cm screed thickening) / 🔴 for renovation without screed requirement (rare) — By 10+cm (insulation 3+ cm and 7+ cm screed)
🟡/🔴 Installation cost: 🟡 for new construction and renovation with new screed layer 🔴 for renovation requiring complicated old screed replacement
🟢/🔴 Installation simplicity: 🟢 for new construction and renovation with new screed layer 🔴 for renovation requiring complicated old screed replacement
🟡 Material restrictions: Floor coverings with high thermal conductivity
🟡 Risk of window condensation: With normal heating
🟡 Cooling compatibility¹: Medium condensation risk with high humidity
Wall Heating (Hydronic) Drawbacks
Summary:
5🟡 for new construction
7🟡 for renovation
🟡 Space usage comfort: Wall usage constraint
🟡 Reduction in useful room area: By plaster layer about 2 cm
🟡 Material restrictions: Wall and finishing materials with high thermal conductivity
🟡 Installation cost
🟡 Materials and equipment cost
🟢/🟡 Installation simplicity: 🟢 for new construction. 🟡 for renovation — Requires groove cutting and possibly deepening electrical wiring where crossing pipescrossing pipes
🟢/🟡 Installation cost: 🟢 for new construction 🟡 for renovation
¹ Cooling Compatibility Note: Compatibility ratings (Poor, Medium, Good) assume use in combination with ceiling fans set to upward flow. This mode creates gentle circulation, enhancing cooling distribution and minimizing drafts from chilled surfaces (15-20°C water). Without fans, using these systems for cooling is generally less effective and carries higher condensation risks.
Underfloor and Wall Heating Combined with Reduced Electricity Rates
As discussed previously, leveraging high thermal mass with reduced electricity rates dramatically cuts heating/cooling costs.
Active built-in thermal battery refers to using the building’s mass (floors, walls) integrated with a heating/cooling system (like underfloor/wall pipes) to both effectively charge and dissipate thermal energy over a large area. A thermal battery without effective charging is considered passive (e.g., just a massive wall without embedded pipes).
Hydronic underfloor and wall heating excel here:
- They are low-temperature systems.
- They create a high-capacity active built-in thermal battery.
- They possess high thermal inertia, resulting in a slow but very stable microclimate.
- The large mass (screed/walls) charged during low-cost periods releases energy throughout the day.
- The large dissipation area provides uniform heating/cooling via radiation and gentle convection.
Our Experience: Before moving to Serbia, we lived with both forced-air and high-temperature radiator systems. Our current underfloor heating is vastly superior in comfort and efficiency.
Preliminary Prioritization of Space Heating Systems
Based on our analysis, aiming for optimality and comfort, central ducted forced air and high-temperature radiator heating have significant drawbacks, especially for medium to large properties, and low thermal inertia, making them unsuitable for cost optimization using reduced-rate tariffs. Ductless forced air avoids duct losses but retains issues with convective comfort, noise, aesthetics (especially in larger properties), and low inertia. Therefore, we generally do not recommend forced air systems (neither ducted nor ductless) or high-temperature radiators as primary solutions compared to radiant options for achieving OptiHeatX goals.
Personal Observation: Our previous experiences align completely. Underfloor heating, as implemented in our current home following OptiHeatX principles, utterly outclasses those other options in terms of comfort and efficiency.
For the remaining systems, our priority order is:
Wall heating (hydronic)
Offers the largest potential dissipation area and allows higher charging temperatures for the thermal mass compared to floors. Recommended as the top priority where feasible and sufficient wall space exists.
Underfloor heating (hydronic)
Provides excellent comfort, is completely hidden, and effectively utilizes floor mass for thermal battery. Best choice when ceiling height accommodates the required screed thickness.
Low-temperature radiator heating
A fallback option if underfloor or wall heating is impractical, particularly for small properties. However, be aware of significant aesthetic and space-use compromises due to the large size of low-temperature radiators, especially problematic in larger properties.
Final Recommendations
Underfloor Heating
On Concrete/Block Slabs: Installing underfloor heating directly onto concrete or block inter-floor slabs is often ideal. The inherent thermal mass of the slab aids heat distribution, potentially allowing a single system to effectively heat/cool both the level below and the level above, often without needing extra insulation between floors.
Tip: Using ceiling fans (upward flow mode) can further enhance this multi-level effect – aiding heating on the lower floor and cooling on the upper floor.
Wall Heating
Heated Windowsills (Condensation Prevention)
Heating the windowsill area and the wall directly beneath it is highly effective for preventing window condensation, especially in cold weather. This warms the window’s inner surface and adjacent air, reducing the critical temperature difference.
Key: Use thermally conductive windowsill materials (stone, tile, metal) to maximize heat transfer from heating elements beneath/behind the sill.
Lower Wall Sections (Efficiency & Practicality)
Heating only the lower third or half of the wall (e.g., up to windowsill height) can be very effective, particularly with thermally conductive walls (concrete, brick, thick plaster).
Benefits: Activates a larger wall area via conduction while minimizing interference with drilling or hanging items higher up.
Prioritize External Walls (Comfort & Condensation)
Focus wall heating efforts on external walls, especially near windows and corners, extending up to windowsill level.
Benefits: Directly combats cold spots and condensation where they are most likely to occur. This approach works well even if the masonry above the heated section is left exposed.
Heated Internal Partitions (Shared Heating)
Heating internal partitions is beneficial if they are massive and thermally conductive (e.g., solid brick/concrete).
Benefits: Allows a single heated wall to serve two adjacent rooms. Heating only the lower section is often sufficient for effective heat distribution.
Best Choice - Combination of Underfloor and Wall Heating
Combining underfloor and wall heating provides the maximum thermal battery capacity and dissipation area.
Our optimal recommendation:
Optimal: New Build / Unconstrained Renovation
Ideal scenario for achieving maximum comfort and efficiency when sufficient ceiling height (10+ cm clearance for screed/insulation) is available:
- Combine underfloor heating with wall heating, focusing wall heating on the lower sections (up to and including windowsill level).
- Prioritize heating external walls and consider adding some internal partitions for enhanced thermal mass interaction.
- Use thermally conductive windowsill materials if heating the sills directly.
Compromise: Constrained Renovation
When underfloor or extensive wall heating is limited by existing conditions (e.g., low ceilings, structural issues):
- Compensate by maximizing the heated wall area wherever feasible.
- Use low-temperature radiators only as a last resort due to their drawbacks (especially in larger spaces).
- Target: Aim for a total heated surface area (floor + walls + radiators) that is at least 25% larger than the room’s floor area to ensure adequate low-temperature heat distribution.
Our additional recommendations:
Heated Windowsills
To combat window condensation, actively heat the windowsills and the wall sections directly below them, especially for larger windows or in humid climates. This significantly reduces condensation risk. Ensure you use thermally conductive windowsill materials (e.g., stone, tile, metal) to maximize the effectiveness of heating elements integrated beneath or behind them.
Bathroom Heating
Increase the heated wall area (e.g., higher up the wall) in bathrooms by an additional 25-50% compared to other rooms for enhanced warmth and comfort, without needing a separate zone. Ensure an airtight, closed door.
Learn optimal towel warmer integration in our product Guide:
Zone Heating
Recommended Zoning: Large Areas
We recommend zoning only by floors or modules (e.g., a winter-use section, separate living units, heated garage). Avoid zoning individual rooms within a single climate zone where air/moisture transfers easily.
Discouraged: Micro-Zoning
Creating separate zones for slightly warmer/cooler rooms within the same overall space is generally ineffective and often a marketing trap.
Heating Unused Zones: Learn how to optimally manage heating zones that may be unused for extended periods (for safety and cost savings) in our product Guide:
Ready to take the next step and design your own optimal heating and cooling system?
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