Will a heat pump work with microbore pipes?

As installers of air source heat pumps we are often asked whether we will need to change a customer's pipework in order to install a heat pump. In this article we explore microbore pipework, plastic vs copper and the way to tell what size pipework you have.

What is microbore pipework?

If your house was built or renovated after about 1990, there is a chance that you have microbore pipework. Housebuilders realised that with better insulation, the amount of heat needed to heat each room could be delivered to the radiator in narrow, plastic pipes.

The problem for heat pumps is that the water that flows around in your heating system doesn't get as hot as with a gas boiler, so we need to get more water to your radiators, faster. And if too much water goes down a narrow pipe quickly, it is noisy and who wants to hear their heating water gushing around their house?

How can I tell if my house has microbore pipework?

As above, the first clue is the age of the house - 1990 or newer. But the second way is to see if the pipes that come out of your radiators are nearer in size to your pinkie (littlest finger), or your thumb.

If it's your thumb, then you have 15mm pipework. If smaller, then it's microbore.

Does this mean I need to change my pipework?

Most often not. If your heat loss is very high and you have very little space for a buffer cylinder, then we might need to change pipework, but typically, with the right design, we can make your existing pipework work.

To find out, you will need to have a heat loss survey carried out. We can do that for you and the journey starts with a Discovery call, which you can book via this link.

Other pipework issues

Typically when you can see 15mm copper pipes coming to the radiators in a pre-1990 house, it's a pretty safe bet that the house has a spine of 22mm copper pipework with 15mm to each radiator. This is perfect for a heat pump.

Experience has thrown up a few other pipework issues across the 7 years we've been installing heat pumps. Here are a few of them:

• We've worked on houses that used to be multiple properties and then combined into 1 and the join was made with plastic pipework. The problem with plastic is that it has a smaller inside diameter than a copper pipe, so less water can get down.

• Where extensions have been built, often the extension radiators are added to the circuit with plastic pipework.

Here are our team working on a Victorian semi in Egham, Surrey where there was an interesting mix of pipework under the floor.

How to avoid problems

1. Make sure your heat pump installer does a heat loss calculation and sizes the pipework correctly

2. Tell your installer as much as possible about the house and anything you know about extensions or alterations

3. If your house has a complex history of extensions and upgrades, set aside some contingency money for pipework alterations that might be needed.

Ready to explore whether a heat pump is right for your home? Schedule your Discovery call with us today and take the first step toward low-carbon heating.

FAQs About Pipework and Heat Pumps

I’ve heard heat pumps won’t work with old pipework — is that true?

Not true. Heat pumps can work very well in older homes, even with existing pipework. The key is making sure the system is designed properly. In some cases, we may recommend changes — for example, if the pipes are very narrow microbore or if extensions were added with plastic pipework. But in most homes, especially with standard copper pipes, a heat pump can be fitted without major alterations.

What exactly is microbore pipework?

Microbore pipework is thinner piping, often used in homes built or renovated after 1990. It works well with gas boilers, but because heat pumps use lower water temperatures, microbore can sometimes struggle to deliver enough flow quietly.

How can I tell if I have microbore pipework?

The quickest check is the size of the pipes under your radiators. If they’re closer in size to your little finger, they’re probably microbore (around 8–10mm). If they’re closer to your thumb, that’s 15mm — a much better fit for a heat pump.

Do I always need to replace my pipework for a heat pump?

Not always. In most homes we can use your existing pipework, especially if it’s standard 15mm or larger copper pipes. In cases with microbore or unusual layouts, we’ll carefully assess whether changes are needed — but often the right system design means no major alterations.

Can plastic pipework be a problem?

Plastic pipes can sometimes restrict water flow because their internal diameter is smaller than copper. This can matter if your home has had extensions or alterations. During a heat loss survey, we’ll identify any potential issues so there are no surprises.

How do I make sure my installation goes smoothly?

Choosing an experienced installer is key. We always carry out a full heat loss calculation, check your pipework properly, and talk through what we find. If your home has had lots of extensions or upgrades, it’s wise to budget a little contingency just in case.