Heat From Air

Do air source heat pumps work with existing radiators?

Do air source heat pumps work with existing radiators?

Do air source heat pumps need new radiators, or can they work with existing radiators? Find the answers in this expert blog.

Are new heat pump radiators required when replacing a boiler with renewable technology? This a key question to ask, especially before potentially installing an inappropriate system and making a job more costly than anticipated. 

Heating your home with an air source heat pump relies on low flow temperatures. But if you have low temperatures, then you need a larger surface area. Heat pumps have a lower flow temperature of around 35°C to 45°C, whereas a traditional radiator system warmed using gas boiler central heating would have flow temperatures of around 75°C. 

Underfloor heating is arguably the best solution in combination with a heat pump, but in existing homes where certain floor coverings, such as thick carpets or solid uninsulated floors, present less feasible conditions.

So, any radiator, old or new, needs a larger surface area to allow the heat to transfer effectively around a room.

Do air source heat pumps work with radiators?

Air source heat pump systems work with radiators, but you need to ensure that the radiators operate at lower temperatures. Consider this carefully when weighing up whether to invest in an air source heat pump or gas boiler

Most air source heat pump installations are more efficient when producing low temperatures. The heat pump works by compressing gas to create heat. Hotter gas requires higher pressure. Therefore, the harder the heat pump works, the less efficient it will be.

When swapping a boiler for an air source heat pump central heating system, it’s far better to have a small amount of heat for prolonged periods rather than a high temperature for shorter times.

With radiators not covered by boxing, the design requires larger surface areas to produce lower flow temperature heat in the room.

In this scenario, you may need to change single-panel radiators to double or triple-panel radiators, or possibly just add an extra radiator to the room.

It’s also worth noting that different alloys or metals such as aluminium, conduct heat quicker than steel and are sometimes better suited to more compact low-temperature radiators. However, they will also be more expensive than steel ones.

Double and triple-panel radiators are more likely to be suitable for use with an air source heat pump than single-panel designs.

What are the best radiators for air source heat pumps?

Any radiators with the correct output characteristics (such as those with a lot of surface area) provide the best radiators for air source heat pumps. And as mentioned above, double, and triple-panel radiators are more suitable than single-panel radiators.

Radiators with low surface areas may not have as much efficiency at the low flow temperatures that heat pumps provide. Common types of low surface area radiators include those with decorative columns, such as towel rails, single rails, and some designer radiator panels. 

While each of these radiators will technically work with an air source heat pump, they won’t work as effectively. In the design phase of the plans, we’ll discuss what radiators work best with the heat pump you’re installing. So, remember to ensure you have the correct compatibility by confirming with your heat pump installation team.

How much can you save with a heat pump?

There is not one specific size for the best radiator to work with an air source heat pump in an average room, as it depends on the heat loss calculations on a room-by-room basis.

Various factors, such as plumbing, position (especially with boxes around them), and surface (paint), all affect the sizing calculations.

Standard radiators deliver a specific amount of heat at a temperature difference of 50°C between the average flow temperature in the radiator and the room temperature. Therefore, if you buy a 1000W radiator and want the room temperature to be 20°C, it will deliver 1000W with the radiator flow temperature at 70°C (50°C temperature difference).

Heat pumps have an average flow temperature of 40°C, which means the temperature difference between that and the desired room temperature (20°C) is only 20°C. The result will only get 304W (the resizing factor, see below) from a 1000W radiator.

So, if the calculated heat loss in the room is 600W, you will need to install a radiator with a minimum output rating of at least 2000W. (Two 1000W radiators.)

Many manufacturers offer resizing graphs that you can reference to see if your heat pump radiators will perform appropriately.

Usually, you would use radiators with two or three panels and two or three convectors. The two-panel and two-convector radiators are known as Type 22 or K2 radiators. These types are common to fit on heat pump central heating systems.

When should you replace radiators?

Older homes had radiators fitted without much attention to the heat rating of the radiator. They may have been sized to fit under windows or simply supplied as they were ‘in stock’ or ‘on sale’.

If an existing home has specific energy efficiency measures such as double (or triple) glazing, modern draught-proof doors and insulation in cavities and lofts, then existing radiators (even where incorrectly sized) may be fine and not need replacing, so long as they’re in good working condition.

That said, the pipework to the radiators may need changing (More on this later).

When you get your survey for a heat pump installation, we’ll always perform a room-by-room heat loss calculation. We’ll also note the size and rating of the radiators in each room. These figures will then determine whether the radiators need changing.

Installation is suitable for existing radiators but only at a higher flow temperature, such as 50°C. Therefore, it’s worth asking how many radiators would need alteration for the flow temperature to be 45°C or even 40°C. This alteration will help improve the efficiency of the heat pump.

Alternatively, if you don’t want to install all new radiators, a high-temperature heat pump can provide you with another option. Get in touch to find out more.

How much will it cost for new heat pump-compatible radiators?

Standard radiators cost around £80 – £300 (depending on size and brand) while replacing radiators is not difficult for an experienced plumber or heating engineer.

Choosing radiators made from aluminium will be the best option to work with a heat pump. Cast iron and steel will work and might be cheaper, but you may need to check if these materials are appropriate for your house’s needs.

The anomaly here is the unknown hidden pipes. If you need to change the pipework (see below), you must find a route from the heat pump to each room. Working in ceilings is potentially easy. But skirting removal, floor lifting, and chasing walls can be disruptive and costly to fix.

Again, we will discuss everything during the planning stage to keep you in the loop.

Do radiator pipes also need to be replaced?

If you are evaluating your home for potential heat pump central heating installation, then 22mm pipes are best. 15mm pipes should still be ok, but anything smaller, like 12mm or 10mm microbore piping, could present design and performance issues.

This issue arises because there are two ways to deliver more heat via water to a room. Either you make it hotter, or you deliver it faster. Boilers have a hot flow temperature. Therefore, the pipe size may be specific for that level of heat. But with heat pumps, the ‘hotter’ option brings lower efficiency. So, the only remaining option is increased flow. Increased flow means larger pipes.

Small pipes could have pressure and balancing issues alongside potential noise problems, depending on the number of rooms and pipe length. Thermal cameras help map the route of the pipes.

Many volume homebuilders will have used the smallest possible radiators and the cheapest pipework. This means that many so-called ‘new homes’ can be challenging to convert to an efficient heat pump system without disruption and pipe changing.

You may be able to get the plumbing plans from the builder if they have them, which would certainly help determine the central heating schematic and the pipe sizes.

What are the 'hidden' cost implications if the pipework is replaced?

Heating engineers and plumbers are qualified to do pipework, and some electrical and mechanical work, such as hanging radiators and boilers. Any other skills are supplementary.

So, if you expect them to replace chased tiling, repair flooring, fit carpets, plaster walls, repair roofs or any of the other tasks, then expect to pay a bit more. Always ask the installer what’s included in the requirements of the project.

Final thoughts

We hope this article has helped anyone wondering whether air source heat pumps work with existing radiators and other features. Whether you’re considering an update to your home heating or finding a more environmentally friendly solution, heat pump radiators are ideal, with correct radiator requirements in place.  

As a quick recap, in most heat pump radiator cases, existing radiators should work with a heat pump providing it can produce low temperatures. Plus, a government grant of up to £5000 is available to put towards replacing your boiler with a more environmentally friendly heat pump providing certain criteria before installation. 

To get a quote for heat pump installation at your house, contact our friendly team at Heat From Air, and we’ll happily handle everything for you.

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