Heat Pumps & Fabric First: Why Your Irish Home Needs a “Jacket” Before a Heater

I have a confession to make. Until several years ago, I thought I understood how heating a house worked. Ideally, it went something like this:

Step 1: It gets cold outside (because: Ireland).

Step 2: You press a button on a white plastic box on the wall.

Step 3: A magical machine in the cupboard makes a rumbling noise.

Step 4: The house gets warm.

Step 5: You pay a bill that makes you cry slightly less than your rent/mortgage.

Simple, right? But then I decided to look into retrofitting. Specifically, the government’s grand plan to stop us burning dinosaur juice (oil and gas) and start using electricity to heat our homes via the Holy Grail of modern engineering: The Heat Pump.

And I fell down a rabbit hole. A deep, dark, insulated rabbit hole.

It turns out, putting a heat pump into an old Irish house isn’t like swapping a AAA battery for a AA. It’s more like trying to put a Ferrari engine into a donkey cart. If you don’t upgrade the cart first, the engine will explode, the cart will disintegrate, and the donkey will be very confused.

Today, we are going to talk about the physics of warmth, why your radiator is lying to you, and why the phrase “Fabric First” is the most important thing you’ll read this year.

The Leaky Bucket Theory

To understand why retrofitting is hard, you have to understand the Battle of the Bucket.

Imagine your house is a bucket. Heat is water. Your heating system (boiler or heat pump) is a tap pouring water into the bucket.

The goal of “comfort” is to keep the water level in the bucket high. But here’s the problem: Your bucket has holes. Lots of them. The walls, the roof, the windows, the drafty letterbox—these are all holes letting the water (heat) leak out.

For the last 50 years, the Irish solution to the Leaky Bucket problem was simple: Get a massive tap.

We installed oil and gas boilers that are essentially flamethrowers in a box. They pump heat into the house so aggressively (at 70°C+) that it doesn’t matter that the walls are leaking like a sieve. We just brute-force the temperature up. It’s inefficient, expensive, and terrible for the planet, but it works.

Enter the Heat Pump.

The Ninja vs. The Gorilla

If an oil boiler is a Gorilla that smashes through the cold, a Heat Pump is a Ninja. It is precise, highly efficient, and relies on steady technique rather than brute strength.

A heat pump doesn’t “make” heat; it moves it. It steals low-grade heat from the air outside (even when it’s freezing), compresses it to upgrade the temperature, and moves it inside. Because it’s moving heat rather than creating it from scratch, it is incredibly efficient. For every 1 unit of electricity you put in, you get 3 to 4 units of heat out. This is called the Coefficient of Performance (CoP).

But there is a catch. The Ninja cannot lift heavy weights. A heat pump works best when delivering water at 35°C to 45°C. Compare that to the Gorilla’s 75°C.

If you put a Ninja (Heat Pump) into a house designed for a Gorilla (Leaky Bucket), the Ninja will try to work at maximum capacity 24/7 to keep up with the heat loss. It will fail. The house will be cold, and your electricity bill will look like the GDP of a small nation.

This is why the SEAI grant guidelines are so obsessed with something called the HLI.

The Bouncer: The Heat Loss Indicator (HLI)

The SEAI (Sustainable Energy Authority of Ireland) has a bouncer at the door of the Heat Pump Party. His name is HLI.

The Heat Loss Indicator measures how quickly your home loses heat per square meter. It’s not about how efficient your heating system is; it’s purely about the “Fabric” of the house—the walls, roof, and floor.

• HLI > 2.3: You are not getting in. Your house is leaking too much heat. If you install a heat pump now, you will be miserable and poor.
• HLI ≤ 2.0: Welcome to the VIP section. Your house holds heat so well that a heat pump will hum along efficiently, costing you peanuts to run.

This brings us to the Golden Rule of Retrofitting: Fabric First.

Before you even think about buying a heat pump, you have to fix the bucket. You have to plug the holes. This is why “Heat Pump Ready” is actually a misnomer. It should be “Insulation Finished.”

Step 1: The Hat (Attic Insulation)

Heat rises. If you remember nothing else from physics class, remember that. If your attic isn’t insulated, you are essentially heating the sky. It is the cheapest, easiest upgrade you can make. It’s low-hanging fruit, but for your house.

Step 2: The Jacket (Wall Insulation)

Most Irish homes built before 2007 have walls that act as thermal bridges, transferring heat straight to the garden. You have three options here:

1. Cavity Pump: Injecting beads into the gap in your walls. Quick, cheap, effective.
2. Internal Dry Lining: Sticking insulation boards on the inside. You lose a bit of floor space, and it’s messy.
3. The Big Wrapper: This is the gold standard. You wrap the entire outside of the house in rigid insulation and put a new render on top. It’s like giving your house a duvet. If you are looking into external wall insulation Dublin homeowners often find it’s the only way to get a 1970s semi-D down to that magical HLI of 2.0.

We discuss the specific u-values (the science-y way of measuring insulation effectiveness) in our archives, but the gist is: lower is better.

The Hydraulic Nightmare: Why Pipes Matter

Okay, so you’ve insulated the attic and wrapped the walls. The bucket is fixed. Now we just swap the boiler for the heat pump, right?

Wrong.

We need to talk about pipes. Specifically, a terrifying thing called Microbore.

In the 1980s and 90s, builders loved using tiny 8mm or 10mm copper pipes to feed radiators. It was cheap and easy to bend. For a Gorilla Boiler pumping water at 75°C with high pressure, this was fine.

But remember, our Ninja Heat Pump operates at a lower temperature (35°C-45°C). To get the same amount of heat into the room at a lower temperature, you have to pump a much larger volume of water.

Trying to force that volume of water through a tiny 8mm microbore pipe is like trying to drink a thick milkshake through a coffee stirrer. It doesn’t work. The pump screams, the water rushes noisily, and the heat doesn’t get to the radiator. The system trips out.

This is why a Technical Assessment is mandatory. An engineer needs to come in and check if your plumbing is actually capable of handling the flow rates required by the future.

Radiators: Size Matters

There is another issue with the “low temperature” life. Standard steel radiators rely on high temperatures to radiate heat. If you run tepid water (40°C) through a standard radiator designed for scorching water (75°C), the radiator will just sit there looking lukewarm and disappointing.

To fix this, you need Aluminium Radiators.

Aluminium is a superhero metal for heat pumps. It conducts heat about 5 times better than steel. It responds instantly. When the heat pump sends warm water, the aluminium radiator gets hot now. When the room reaches temperature and the heat pump turns off, the aluminium cools down instantly.

This responsiveness is crucial. In a highly insulated house, you don’t want a heavy steel radiator that keeps pumping out heat for an hour after the sun comes out, overheating the room. You want agility. You want the Ninja.

The Money Question

I know what you’re thinking. “This sounds expensive.”

It is. A deep retrofit involves construction work, plumbing, and high-tech machinery. However, the government really, really wants you to do this. That’s why the Climate Action Plan 2024 has ring-fenced massive budgets for this transition.

There are two ways to do it:

1. The Individual Energy Upgrade Grants:

You project manage it yourself. You hire a guy to do the attic. You hire a guy to do the walls. You hire a plumber for the heat pump. You apply for separate grants for each. It’s more work for you, but you have total control.

2. The Whole Home Approach:

This is where a single company manages everything—insulation, windows, heat pump, ventilation—in one go. The grant amounts are often higher here, and the grant is deducted from the price upfront, so you only pay the net cost. Companies offering these home energy upgrades handle the paperwork, the design, and the chaos.

Is it worth it? CSO data on Building Energy Ratings shows that moving from a BER of E to a B2 or A can slash your energy bills by hundreds, sometimes thousands, of euros a year. And that’s before we talk about the carbon tax, which is only going one way (up).

The Final Boss: Ventilation

There is one final trap to avoid.

Old Irish houses were “breathable.” That is a polite way of saying they were drafty. The wind blew through the floorboards and out the chimney, carrying moisture with it. It was cold, but the house didn’t get mouldy.

When you seal up the house with modern insulation and airtight windows, you stop the drafts. But if you don’t provide a new way for fresh air to get in, you create a plastic bag. Humans breathe, cook, and shower. That moisture has to go somewhere. If it can’t escape, it turns into mould.

This is why Met Eireann data on our perpetually damp climate is so relevant. We live in a wet country. A “Heat Pump Ready” house must have a planned ventilation system, like Demand Control Ventilation (DCV) or Mechanical Ventilation with Heat Recovery (MVHR). These systems pull stale damp air out and bring fresh filtered air in, without letting the heat escape.

The Future is Electric

The grid is changing. ESB Networks are upgrading the infrastructure to handle a world where we drive electric cars and heat our homes with electric pumps. It’s a massive engineering challenge, but it’s happening.

The beauty of the heat pump is that it connects your home to this green grid. As wind farms generate more power, your heating becomes cleaner every year. An oil boiler will always burn oil. A heat pump installed today will be cleaner in 2030 than it is in 2026.

And once you have the heat pump, you have electrified your heat. The next logical step? Generating that electricity yourself. This is where the synergy with Solar Panels Dublin really shines—generating your own power to run your own heat pump is the ultimate closed loop.

Retrofitting is complex. It involves physics, plumbing, and a bit of chaos. But living in a warm, healthy house that costs peanuts to run? That’s worth the hassle.

Also, the Ninja is much quieter than the Gorilla.

If you want to stop heating the sky and start heating your home, get in touch with us today to start your journey and reduce your bills…now.