How do you set heat pump flow temperature?
Last Updated: October 26, 2026
Quick Summary
Heat pump flow temperature is the temperature of water leaving your heat pump and travelling through your heating system. Set it by accessing your system's control panel or app, adjusting in small 2-3°C increments, and monitoring your home's heating performance over 24 hours.
Heat pumps work best at lower flow temperatures than boilers, typically 35-45°C rather than 60-65°C
Your radiator size is the limiting factor: large radiators allow lower temperatures, smaller ones need hotter water
Weather compensation automatically adjusts flow temperature based on outside conditions to match heating demand
Always adjust in small increments and wait 24 hours between changes to let your system settle
Professional surveys help determine the right flow temperature for your specific property and radiator setup
Table of Contents
What is heat pump flow temperature and why it matters
Heat pump flow temperature is the temperature of the water leaving your heat pump and travelling through your heating system. It's the single most important setting for how efficiently your system runs.
Think of it this way: your heat pump is like a water heater. The hotter the water it produces, the harder it works and the more energy it uses. Set the flow temperature correctly, and your system runs efficiently. Set it too high, and you're paying for wasted energy.
Most heat pumps work best at lower flow temperatures than traditional boilers. A gas boiler might push water out at 60-65°C. A heat pump often performs best at 35-45°C. That lower temperature is where the efficiency gains happen.
Why does this matter? Because flow temperature directly affects your energy bills and how well your system heats your home. Get it right, and you'll see the savings. Get it wrong, and you're leaving money on the table.
Finding the best heat pump flow temperature for your system
The best heat pump flow temperature depends on three things: your radiators, your insulation, and how cold it gets outside.
Radiator size matters most. If you have large radiators (typical in older properties), you can use a lower flow temperature and still heat your home effectively. Smaller radiators need hotter water to deliver the same warmth. This is why understanding your radiator setup is the first step.
Insulation changes the equation. A well-insulated home needs less heat overall, so lower flow temperatures work fine. A poorly insulated property might need higher temperatures to compensate. This is why many installers recommend improving insulation before or alongside a heat pump installation.
Outside temperature affects settings too. On mild days, you need less heat. On freezing days, you might need more. This is where weather compensation comes in, a feature that automatically adjusts your flow temperature based on the weather.
Most installers set an initial flow temperature between 40-50°C as a starting point. From there, you monitor how your home heats and adjust. There's no single "best" temperature that works for every property.
Heat pump flow temperature depends on your radiators, insulation, and local weather conditions.
Factor | Impact | Typical range |
Large radiators | Allow lower flow temperature | 35-40°C |
Small radiators | Require hotter water | 50°C or higher |
Well-insulated home | Needs less heat overall | Lower temperatures work |
Poorly insulated home | Needs more heat | Higher temperatures needed |
Mild day outside | Reduced heating demand | 35°C |
Freezing day outside | Increased heating demand | 50°C |
Understanding heat pump weather compensation settings
Weather compensation is an automatic system that adjusts your heat pump's flow temperature based on outside temperature.
M Price Plumbing & Heating Limited
On a mild day (say, 10°C outside), the system might set flow temperature to 35°C. On a freezing day (say, -5°C outside), it might increase to 50°C. The system does this automatically without you having to touch anything.
This feature exists because your heating needs change with the weather. On mild days, you need less heat. On cold days, you need more. Weather compensation matches your system's output to actual demand, which reduces energy waste.
Most modern heat pumps have this feature built in. It's controlled through a curve, a setting that tells the system how to respond to temperature changes. A shallow curve means the system doesn't change flow temperature much as weather changes. A steep curve means bigger adjustments.
The right curve depends on your property's insulation and radiator size. This is where professional setup matters. An incorrectly configured curve will either waste energy or fail to heat your home properly on cold days.
Setting heat pump flow temperature for radiators
Your radiators are the limiting factor for how low you can set flow temperature.
Large radiators (like those in older properties) can deliver enough heat at 35-40°C. Smaller radiators need hotter water, sometimes 50°C or higher. If your radiators are undersized for a heat pump, you have two options: raise the flow temperature, or upgrade the radiators.
Many people worry about needing to replace all their radiators. In reality, most properties can work with existing radiators if you set flow temperature appropriately. The trade-off is slightly higher energy use compared to a property with perfectly sized radiators.
Heat loss surveys from certified engineers help determine the right radiator size for your property. At Heatgeek Wales, we use data-backed heat loss calculations to design systems that work with your existing radiators whenever possible.
To find your radiator size, look at the manufacturer's label on each radiator (usually on the side or back). If you can't find labels, a professional survey will measure them properly. Once you know your radiator sizes, you can calculate the minimum flow temperature your system needs.
Step-by-step: adjusting your heat pump flow temperature
Before you start: what you need to check
Before you adjust anything, gather this information:
Your radiator sizes (in BTU or watts)
Your current flow temperature setting
Your home's insulation type (solid walls, cavity walls, loft insulation, etc.)
Outside temperature on the day you're adjusting
You'll also need access to your heat pump's control panel or app. Most modern systems have a digital interface where you can view and change settings. Some older systems use a physical control panel.
Check your heat pump manual or contact your installer if you're unsure how to access settings. Never adjust anything without knowing what you're changing.
Accessing your system settings
Most heat pumps have a control panel on the unit itself or a wireless thermostat in your home.
Look for a menu option labelled "flow temperature," "supply temperature," or "heating settings." The exact name varies by manufacturer. Your manual will specify where to find it.
If your system has a smartphone app, you can usually adjust settings through the app instead. This is often easier than using a physical panel.
Write down your current setting before you make any changes. That way, if something goes wrong, you can revert to the previous temperature.
Making the adjustment and monitoring the change
Adjust flow temperature in small increments, no more than 2-3°C at a time.
Make one change, then wait at least 24 hours before adjusting again. This gives your system time to settle and your home time to respond. Monitor your heating performance: Is your home reaching the target temperature? Are radiators getting hot enough?
If your home isn't heating properly, increase flow temperature by 2-3°C. If your heating bills seem high, decrease it slightly. The goal is finding the sweet spot where your home stays warm without wasting energy.
Keep notes of your adjustments and how your home responded. This information is valuable if you need to troubleshoot later or if a technician needs to review your system.
Heat pump flow temperature troubleshooting
Problem: Home not heating properly even at high flow temperature.
This usually means your radiators are too small for your heat pump, or your insulation is poor. Raising flow temperature further will waste energy without solving the problem. Consider a professional survey to assess your actual heating needs.
Problem: Heating bills higher than expected.
Flow temperature set too high is the most common cause. Lower it by 3-5°C and monitor for a week. If bills don't improve, the issue might be something else, poor insulation, air leaks, or a system configuration problem.
Problem: Radiators stay lukewarm even at normal flow temperature.
Check that your pump is running and that radiators aren't blocked with air. Bleed air from radiators using the bleed valve at the top. If that doesn't help, your system might have a circulation problem requiring professional attention.
Problem: System keeps increasing flow temperature automatically.
This usually means weather compensation is set too aggressively. Check your weather compensation curve settings. A less steep curve will reduce unnecessary temperature increases.
Getting professional support with your heat pump settings
If you're unsure about any adjustments, or if troubleshooting hasn't worked, professional support is worth the investment.
A qualified engineer can review your system configuration, check your radiator sizes against your heating demand, and optimise flow temperature for your specific property. They can also identify other issues, poor insulation, air leaks, or system faults, that affect heating performance.
At Heatgeek Wales, we provide 24/7 remote monitoring and optimisation as part of our service. This means our team can track your system's performance continuously and make adjustments to improve efficiency. If issues arise, we identify them before they become problems.
Many homeowners find that professional setup and ongoing monitoring is an investment in getting your system right from the start.
Frequently Asked Questions
What is the best flow temperature for a heat pump?
The optimal heat pump flow temperature depends on your heating system and property. Most systems perform efficiently between 35°C and 55°C. Older properties with radiators often need higher temperatures (45-55°C), whilst newer homes with underfloor heating work well at lower temperatures (35-45°C). Lower flow temperatures reduce energy consumption and running costs, so aim for the lowest temperature that keeps your home comfortable. Your installer can recommend the ideal setting based on your specific setup.
How does weather compensation affect heat pump flow temperature?
Weather compensation automatically adjusts your heat pump flow temperature based on outdoor conditions. On mild days, the system reduces flow temperature to save energy; on colder days, it increases it to maintain comfort. This feature optimises efficiency throughout the year without manual adjustment. Most modern heat pumps have weather compensation built in.
Can lowering the heat pump flow temperature reduce running costs?
Yes. Lower flow temperatures reduce the energy your heat pump consumes, directly lowering your heating bills. However, the temperature must remain high enough to adequately heat your home. The sweet spot is the lowest temperature at which your property reaches your desired comfort level. Many homeowners find they can reduce flow temperature by 5-10°C without losing comfort, resulting in meaningful savings on energy costs over time.
What should I check before adjusting my heat pump flow temperature?
Before making changes, note your current settings and room temperatures. Check your installer's documentation or system manual for recommended ranges. Ensure your heating system (radiators or underfloor heating) is appropriate for the temperature you're considering. Make one small adjustment at a time (typically 2-3°C), wait 24-48 hours to observe the effect, then adjust further if needed. Document each change so you can revert if necessary.
Getting your heat pump flow temperature right is the difference between a system that works and one that works brilliantly. Start with the settings your installer recommends, monitor your heating performance, and adjust gradually. If you're not confident making changes yourself, a professional survey will identify the optimal settings for your property and ensure your system delivers the efficiency gains you expect.
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