Heat Pumps Need a Renovation — Not Just a Swap

The Myth of the Simple Swap

Sales brochures show a clean transaction: old gas boiler out, sleek heat pump in. Same pipes, same radiators, same home. Just greener.

The reality is different. A heat pump is not a boiler that happens to run on electricity. It is a fundamentally different heating machine that requires a fundamentally different heating system inside your home. And that difference often means a major renovation.

The gap most buyers miss: A gas boiler sends water through your radiators at 60–80°C. A heat pump needs to run at 35–45°C to be efficient. At those temperatures, your existing radiators are too small to keep your rooms warm. You need more surface area. A lot more.

Why Temperature Changes Everything

The Physics in One Sentence

Heat flows from hot to cold. The warmer your radiator is compared to the room, the faster heat transfers. Cooler radiator = slower heat transfer = you need more surface area to deliver the same warmth.

Gas Boiler vs Heat Pump: The Numbers

Parameter Gas Boiler Heat Pump (efficient)
Flow temperature 60–80°C 35–45°C
Return temperature 50–60°C 30–35°C
Temperature difference to room (at 20°C) 40–60 K 15–25 K
Heat output per m² of standard radiator ~1,200 W ~350 W
Radiator area needed for same heat 1× 3–4×

At 35°C flow temperature, a standard steel panel radiator outputs roughly one-third of the heat it does at 70°C. To deliver the same 2 kW that heats your living room, you need three times the radiator surface — or a completely different distribution system.

What "More Surface Area" Actually Means

There are three ways to solve the surface-area problem. All three involve construction work.

Option 1: Underfloor Heating (Best Performance, Most Work)

Aspect Details
Surface area 30–50 m² per room (the entire floor)
Flow temperature 30–35°C — perfect for heat pumps
COP impact +0.5 to +1.0 higher than with radiators
Installation Floor up: screed removal, pipe laying, new screed, new floor covering
Cost per room €1,500–€3,500
Whole house (100 m²) €8,000–€20,000
Disruption You move out for 2–4 weeks. Every floor comes up.

Underfloor heating is the gold standard for heat pumps. The huge surface area lets the heat pump run at its most efficient low temperatures. But it is not a retrofit. It is a gut renovation.

Real-world note: In Hungary, Germany, Poland, and much of Central Europe, homes built before 1990 have concrete floors with no insulation beneath. Installing underfloor heating in these homes often requires adding floor insulation first — otherwise you are heating the ground beneath your house. That adds €15–€30/m² and 5–10 cm of floor buildup, which may mean cutting doors, adjusting stairs, and raising skirting boards.

Option 2: Oversized Radiators (Moderate Work, Moderate Performance)

Aspect Details
Surface area 2.5–4× existing radiator volume
Flow temperature 45–50°C (compromise for radiators)
COP impact Still decent, but 10–20% lower than underfloor
Installation Remove old radiators, install larger ones, may need pipe resizing
Cost per room €400–€1,200
Whole house €3,000–€8,000
Disruption 2–5 days per room. Dust. Wall damage. Repainting.

This is the "compromise" route. You keep a radiator system but make everything bigger. That often means:

The hidden problem: Your existing pipes may be too narrow. A heat pump circulates a much larger volume of water at lower temperature, and the hydraulic resistance of old 15 mm pipes can be too high. You may need to replace the pipework — which means opening walls.

Option 3: Wall or Ceiling Heating (Niche, Expensive)

Aspect Details
Surface area Entire wall or ceiling surface
Flow temperature 30–35°C
Installation Drywall removal, pipe embedding, new drywall, repainting
Cost per room €2,000–€4,000
Disruption High. Every wall or ceiling surface is affected.

Wall and ceiling heating works well but is the most invasive option. It is rarely chosen for retrofits unless the home is already being fully renovated.

The Full Renovation Checklist

Replacing a gas boiler with a heat pump in a typical 1980s European home often requires more than just new emitters. Here is the honest checklist:

Item Why Needed Typical Cost
New emitters (underfloor or oversized radiators) Low-temperature heat distribution €3,000–€20,000
Pipework resizing Higher water volume, lower resistance €1,000–€5,000
Hydraulic balancing Even heat distribution at low temperatures €500–€1,500
Floor insulation (if underfloor) Prevent downward heat loss €1,500–€3,000
New hot water cylinder Heat pumps need larger, insulated tanks €1,000–€2,500
Electrical upgrade Heat pump + backup heater = 3-phase, 20–32A €800–€3,000
Outdoor unit pad/base Vibration isolation, drainage, clearance €300–€800
Removal of old boiler + flue Regulatory and safety requirement €300–€600
Room-by-room heat loss calculation Required to size emitters correctly €300–€600
Building permits / compliance Varies by country €0–€1,000
TOTAL (typical range) €8,700–€38,000

This is in addition to the heat pump itself. A typical air-source heat pump costs €6,000–€12,000 installed. The full project — heat pump plus necessary building work — can easily reach €15,000–€50,000.

The number most installers quote: €8,000–€12,000 for the heat pump. The number most homeowners actually pay: €20,000–€40,000 once the building is ready for it.

Why Installers Often Don't Lead With This

Installers are typically paid to supply and fit the heat pump unit, not to manage a whole-house renovation. This creates a structural incentive to scope the project narrowly. Here is what that narrow scope can mean in practice:

What you may hear What it can mean in practice
"Works with your existing radiators" The system may run at 55–60°C, which reduces efficiency significantly compared to a low-temperature design.
"High-temperature heat pump available" A unit that outputs 65°C is available, but your electricity consumption can be 40% higher than at 35°C.
"Minimal disruption" The work may be limited to the boiler room, leaving emitter upgrades for later — at additional cost.
"Subsidy covers most of it" The subsidy typically covers the heat pump unit; the building renovation often remains the homeowner's cost.

High-temperature heat pumps (capable of 60–70°C output) exist. They are marketed as "drop-in replacements" for gas boilers. But they achieve those temperatures by sacrificing efficiency:

Flow Temperature Typical SCOP Annual Electricity (for 10 MWh heat) Cost at €0.35/kWh
35°C 4.5–5.0 2,000–2,200 kWh €700–€770
45°C 3.8–4.2 2,380–2,630 kWh €830–€920
55°C 3.0–3.4 2,940–3,330 kWh €1,030–€1,165
65°C 2.4–2.8 3,570–4,170 kWh €1,250–€1,460

At 65°C, a heat pump uses nearly twice the electricity of one running at 35°C. The whole point of a heat pump is efficiency. Running it at boiler temperatures defeats the purpose. You might as well use direct electric heating — which is cheaper to install and almost as efficient at those temperatures.

When It IS Worth It

Scenario A: You Are Already Renovating

Situation Heat pump fit
New build Perfect. Design for 35°C from day one.
Full floor replacement Ideal time for underfloor heating.
Extension being built Size the new part for low temperature, hybrid system for old part.
Bathroom/kitchen renovation Underfloor heating in wet rooms is standard anyway.

If the floors are already coming up, the marginal cost of underfloor heating is much lower. The expensive part is the disruption, not the materials.

Scenario B: Your Home Is Already Efficient

Home characteristic Why it helps
Built post-2000 with insulation Low heat demand means even modest emitters suffice.
Small, well-insulated apartment Low heat load per room. Existing radiators may be adequate.
Previously retrofitted with insulation See our Insulation First guide — insulation reduces emitter size needed.

A home that needs only 3 kW of heat on the coldest day can get by with smaller emitters than one that needs 10 kW. Insulation is the multiplier that makes everything else cheaper.

Scenario C: You Have a Large Budget and Long Time Horizon

Factor Your situation
Planning to stay 20+ years Long payback acceptable.
No gas grid connection Heating oil and direct electric are worse options.
High solar self-consumption Running the heat pump on your own solar improves economics. See Solar and Heat Pumps.
Environmental priority primary Even at higher cost, emissions are 60–80% lower than gas.

When It Is NOT Worth It

Scenario D: Tight Budget, Quick Decision

Red flag Why it matters
You can't afford €20,000–€40,000 total The heat pump alone won't work well without the building work.
You plan to move within 10 years You won't recover the investment.
You expect "just swap the box" You may be disappointed by performance and bills if the building isn't ready.

Scenario E: Heritage or Rental Property

Constraint Problem
Listed building / monument protection Cannot alter floors, walls, or pipework.
Rental property (tenant pays electricity) Landlord pays for renovation, tenant pays higher bills if done wrong.
Apartment with shared heating system Individual heat pumps rarely viable.

Scenario F: Mild Climate with Cheap Gas

Location Gas cost Heat pump economics
Southern Spain, Portugal Low gas use, mild winters Heat pump savings minimal.
Hungary on regulated gas tariff ~3.5 Ft/kWh equivalent Heat pump electricity at H-tarifa (~35 Ft/kWh) is 10× more per unit of heat.

Hungary specific: At the regulated residential gas price (≈102 Ft/m³, ~10.2 kWh/m³, ≈10 Ft/kWh of heat at 90% boiler efficiency), a heat pump on H-tarifa electricity (≈35 Ft/kWh ÷ COP 4 = 8.75 Ft/kWh of heat) is only slightly cheaper. Once you factor in the €20,000+ renovation, the payback is decades. See our Household Energy Profiles for country-by-country heating costs.

The Honest Cost Comparison

15-Year Total Cost of Ownership

Scenario Upfront Annual Heat Cost 15-Year Total Notes
Keep gas boiler (replace at yr 10) €3,000 €1,200 €21,000 Baseline. Emits ~2.5 tCO₂/yr.
Heat pump + full renovation €30,000 €700 €40,500 Best performance. Emits ~0.5 tCO₂/yr.
Heat pump + oversized radiators €15,000 €850 €27,750 Compromise. May still need some wall work.
High-temp heat pump, no renovation €10,000 €1,100 €26,500 Worst of both worlds. High bills, high emissions.
Direct electric heating €2,000 €2,200 €35,000 Only if no gas and no heat pump budget.

The high-temperature "drop-in" heat pump is the trap. It costs more than keeping gas, saves almost nothing on bills, and still requires electrical upgrades. The full renovation route is expensive but delivers real efficiency. The middle path — oversized radiators with some pipework — is often the pragmatic choice.

What to Ask Your Installer

Before signing anything, get written answers to these questions:

  1. "What flow temperature will the system run at in mid-winter?"

    • If they say 55°C+, ask for the SCOP at that temperature. Then calculate your electricity bill.

  2. "Have you done a room-by-room heat loss calculation?"

    • If no, they are guessing on emitter sizes. Every room is different.

  3. "Will my existing radiators keep every room at 20°C on the coldest day?"

    • If they say yes at 45°C flow, check the math. Most pre-2000 homes: no.

  4. "What pipe sizes do I have, and are they adequate for the water volume?"

    • Old 15 mm pipes may need replacing with 22 mm.

  5. "What is the total project cost including all building work?"

    • Not just the heat pump. Everything.

  6. "What happens if I don't do the emitter upgrades?"

    • Honest answer: higher bills, lower comfort, possible frost damage in unheated rooms.

  7. "Show me the COP at the design flow temperature, not the label COP."

    • Label COP is measured at 35°C. Your system may run at 50°C. The difference is 20–40% efficiency loss.

Bottom Line: The Honest Truth

A heat pump is not a boiler replacement. It is a heating system replacement that happens to include a new machine outside your house.

What sales materials imply What actually happens
Swap the box, save money Renovate the building, then save money — maybe
Works with existing radiators Works poorly with existing radiators; works well after major work
Green and efficient Green and efficient only if installed at low temperature with adequate emitters
Subsidies make it cheap Subsidies cover the unit; the renovation is still yours to pay

The honest sequence for most homes:

1. Insulate (see our Insulation First guide)
   ↓
2. Reduce heat demand
   ↓
3. Calculate actual emitter needs at 35–40°C
   ↓
4. Budget €15,000–€40,000 for the full project
   ↓
5. Get 3–5 quotes that include building work, not just the unit
   ↓
6. If the total cost is too high, keep the gas boiler and insulate instead

The most expensive mistake: Buying a heat pump and running it at 55–60°C to avoid renovation. You pay the premium for the heat pump, you pay for the electrical upgrade, and you get the efficiency of a cheap electric heater. The installer who sold the unit is paid regardless of the outcome.

Last updated: May 2026