Welcome To


Your guide to renewables


There are three main types of heat pumps connected by ducts: air-to-air, water source, and geothermal. They collect heat from the air, water, or ground outside your home and concentrate it for use inside.  

The most common type of heat pump is the Air source heat pumps which transfers heat between your house and the outside air. Today’s heat pump can reduce your electricity use for heating by approximately 50% compared to electric resistance heating such as furnaces and baseboard heaters. High-efficiency heat pumps also dehumidify better than standard central air conditioners, resulting in less energy usage and more cooling comfort in summer months. 

Air-source heat pumps have been used for many years in nearly all parts of the world, but until recently they have not been used in areas that experienced extended periods of subfreezing temperatures. However, in recent years, air-source heat pump technology has advanced so that it now offers a legitimate space heating alternative in colder regions. Let’s take for example Scandinavian countries which have some of the most extreme temperatures in winter. 

Finland is no different. In 2020, the country installed more than 100,000 heat pumps for the first time (the previous record was 76,000), and simultaneously passed the one million heat pump landmark. 

About us:

The focus of this blog will be on Air source heat pumps since they are more affordable than other types of heat pumps and as mentioned above, in recent years air-source heat pump technology has advanced so much, that they are now direct competition to ground or water source heat pumps, due to their lower costs. Furthermore, I have owned 16kw Viessman one for more than two years now and before I made the decision to buy one, I researched this topic thoroughly and I speak from experience so weather you are upgrading your current heating system or planning one from scratch this blog is for you. 

There are a lot of videos and similar blogs either vouching for heat pumps efficiency or denying them completely and I can say with certainty that they are both correct. 

What I mean by this:

Heat pumps will not work if you just slap them on hit the switch and the pump will do its magic, no, to make them work you need to carefully design your system to take most of the heat pumps efficiency. Properly set up system can generate COP (coefficient of performance- more on that later) up to 4 or more which means heat pump will for every Kw of electricity create 4 Kw of heating energy making it 400% efficient. 

Considering the most advanced gas boilers can only reach 100% of their efficiency you can see what all the hype is about, and I can confirm this to be true from my personal experience of using both fossils fueled heaters and heat pumps. 


In this blog I will go through with you on everything you need to know and will provide our carefully designed and completely free tool that will help you calculate and prepare your property before installing a heat pump so you can decide if upgrading to a heat pump is really for you.

Trust me, it’s far simpler and can be quote cheaper than you might think so let us begin. 

What you need to know before you buy: 

What size of a heat pump do I need? 

Contrary to popular belief the average property needs around 6 to 8 Kw load, that’s it, but that depends on how big of a property is and more importantly how well insulated that property is. 

To calculate this, you need to know what your property heat loss is. 

Yes, heat loss calculation will be focus of our research since every heating system design needs to start with heat loss calculation especially for heat pumps.

The “bigger is better” theme does not work with heat pumps, over sizing the unit will cause more compressor cycling, drop in efficiency (COP) and running costs will not justify your investment. 

This calculation will also help you with our second most important topic and that’s sizing your radiators. 

Yes, Heat pumps can work on your current radiator system but please note that you might need to upgrade your radiators for bigger ones or to add additional radiators in order to keep desired indoor temperatures while maintaining high efficiency (COP). 

If you have underfloor heating, you are good to go. 

What is heat pump COP/SCOP

Before we continue with our calculations, I would like to quickly explain what coefficient of performance or COP mentioned previously means.

Note: Formulas presented throughout this blog are for explanatory and research purposes only our tool already utilize all this formulas and does your calculations automatically based on your input, still i encourage everyone to go through them carefully as they will show you that our tool is based on precise math and extensive research, also some of you may even find it fun as i did:)

The Co-efficient of performance (COP) is an expression of the efficiency of a heat pump. When calculating the COP for a heat pump, the heat output from the condenser (Q) is compared to the power supplied to the compressor (W). 

COP = |Q|


COP is defined as the relationship between the power (kW) that is drawn out of the heat pump as cooling or heat, and the power (kW) that is supplied to the compressor. 

So basically, a given heat pump used for heating has a COP = 2. This means that 2 kW of heating power is achieved for each kW of power consumed by the pump’s compressor. The greater the COP the lower is the electric bill. 

Please note that COP is not fixed value for diverse types of heat pumps like mentioned above, no, each heat pump can achieve greater or lower COP based on several factors like outside temperature, desired in door temperature and most importantly system design which we will cover here in detail. 

I’m mentioning this as through this research we will design a system to try and squeeze the most efficiency (COP) out of a heat pump. 



Heat moves from hot to cold by law, so the heat will naturally try to escape your home in the winter either through walls, windows, doors or through ventilation. 

Heat loss calculation will show you exactly how much heat you are losing considering current outdoor temperature and just how much heat you need to deliver to that room in order to keep desired temperature indoors. 

Please note: 

Make sure that your installer conducts proper heat loss calculation for your property before getting further with any installation process. They will need to measure every wall, window, door, thickness and composite of wall insulation and most importantly size of your radiators. This is a lengthy process that would take couple of hours to complete based on the size of your property. Luckily by the end of this article you will gain knowledge to challenge installers since this part of heat pump installation process is so important that you should abort contract immediately if they haven’t done anything close to above mentioned measurements.

I’m saying this because most brands/installers will just sell you a product, install it and set it to “max” in order to meet your expectations heating wise, but the running cost will not justify your investment, you are better off with a gas boiler. 

Heat loss calculation is a complex process, you can hire a company to perform an on-site survey at your location to calculate your heat loss, but the cost of such surveys is quite high, and it takes multiple days in some cases. We created easy to use tool with all the formulas so you can easily calculate your home heat loss very precisely by yourself and according to that size your radiators so that you can buy the correct size of a heat pump and actually make it work (pay off) 

First, we need to tackle the “U” value of materials your property is built of: 

What is U value? 

Thermal transmittance, also known as U-value, is the rate of transfer of heat through a structure (which can be a single material or a composite), divided by the difference in temperature across that structure. The units of measurement are W/m²K. The better-insulated a structure is, the lower the U-value will be. 

This can be applied to walls as well as ceilings, floors roofs even doors and windows. 

Let’s see an example of calculating u value of a wall composite from outside to inside: 


Material Thickness Conductivity
Resistance = Thickness ÷ conductivity
Outside surface   0.040 K m²/W 
Clay bricks 0.100 m 0.77 W/m⋅K 0.130 K m²/W 
Glass wool 0.100 m 0.04 W/m⋅K 2.500 K m²/W 
Concrete blocks 0.100 m 1.13 W/m⋅K 0.090 K m²/W 
Plaster 0.013 m 0.50 W/m⋅K 0.026 K m²/W 
Inside surface   0.130 K m²/W 
Total 2.916 K m²/W 
U-value = 1 ÷ 2.916 = 0.343 W/m²K 

Please note that the above example includes the conductivity (k-values) of building materials, which is crucial for calculating the material U value. The purpose of this blog is to maintain these calculations as user-friendly and straightforward. Therefore, our tool will compute the U value of your walls by allowing you to easily select the materials your wall is made of and specify their thickness, as demonstrated below.


So basically, the lower U value is the better since that will mean that material or composite of materials provides more insulation. 

Note: You need to input U value for your doors and windows manually since they differ to much depending on type and manufacturer. You can find U values by contacting your manufacturer as they are obliged to provide this information with their product. You can also do a quick search on line to find the U value range for your window type (chose higher U value rather then lower just to be on the safe side).

Now that you have U values of your walls, ceilings/roof, floors, doors and windows we can start calculating heat loss room by room. 

Calculating Heat loss: 

Calculating the heat loss is the most vital piece of information, this tells us how big a heat pump you need is going to be or if installing a heat pump to your property is worthy at all. 

Thankfully as mentioned before most property’s require around 6-8 kw. 

So how to calculate the heat loss of a room. 

Now that you have your U values of materials, let’s say outer wall, we need to multiply that number by surface area of that wall and multiply that by temperature difference between indoor desired temperature and lowest outside temperature depending on your region. This difference in temperature is called delta T (ΔT). 

So, for example, if lowest temperature in winter in your region is –5C and you want inside temperature to be 22C, delta T would be total range of temperature from –5 to 22 so that equals to ΔT of 27. 

Let’s see on example below: 

Building component U-value
External wall 0,40 32,30 27 349 


So, we have an external wall composite with U value of 0.40 we multiply that by surface area of that wall 32m2 and multiply that by our ΔT which is as mentioned above 27. 

From this calculation we can see that we are losing 349W of heat through this wall. 

If we do this for all surfaces in the given room, we will have complete heat loss calculation for that room, meaning we will have to provide that much energy(WATS) into that room to maintain 22C. 

Worry not, our tool already includes all these formulas and will do these calculations for you in order to show you just how much heating energy (in Wats) you are losing through a certain surface (External walls, ceiling, Windows…etc.) you simply need to measure those surfaces in m2, exclude any windows/doors that may be on those surfaces for they are entered separately.

Notice on the tool there are fields named natural and mechanical ventilation. 

These are also important for your calculation since there will be some heat lost through opening doors and windows using aspirators, bathroom ventilation etc…
These values are fixed for every property, the tool will utilize your input to calculate heated area and your desired ΔT in order to provide heat loss through selected ventilation.

Repeat this process for every heated room in your property by “Adding new room” button in our tool and you will have complete heat loss for your property in Kw which is crucial when deciding on heat pump size.

Now that we can calculate how much heating energy, we need for each room we can continue to the next step, sizing the radiators. 

Sizing the radiators: 

Heat pumps are a low temperature system so it’s necessary to properly size your radiators in order to achieve efficiency. 

This applies for all heating systems, if you put more radiators or switch current radiators for a bigger one, you can lower the flow temperature significantly and still achieve your set in-door temperature, so basically the lower the flow temperature the greater the efficiency. 

You cannot have too many radiators but of course for the sake of room availability and the esthetics you cannot just cram ten 2m radiators into a 30m2 room, you need to do some calculations. 

This is especially applied to heat pumps, remember at the beginning of this blog we talked about efficiency of heat pump reaching 400%, you cannot do this with any other system even if you upgrade your radiators. 

So basically, the maximum water temperature you want for your heat pump powered radiators is 50c (remember lower is better), heat pumps are just not efficient after that point and as I said you are better off with a gas boiler. I’ll now elaborate how to use conversion factors to adjust radiator size for lower temperatures. 

And like I said if you have underfloor heating then you are golden since that type of heating system does not require more than 35-38c flow temperature anyway which is perfect for a heat pump. 

Now that you have your room-by-room heat loss calculation ready, let’s see if your current radiator system is heat pump ready or if you need to add or upgrade your radiators, or even if a heat pump will work for you at all. 

How to recognize radiator type?

The first thing you need to be aware of is the diverse types of radiators, you have type 11, type 21, type 22 and type 33. 

 If you look down at your radiator you can easily figure out the type of radiator you have. 

Types of panel radiators

If your radiators do not have these fins, you will probably have to upgrade anyway purely due to their age as they will not satisfy the output required for a heat pump.

Utilizing our tool:

Now that you know what type your radiators are you simply need to measure their surface area in m2 by multiplying their height times width and use that surface area in our tool that we provided. 

Remember to do this calculation room by room measuring all radiators in one room.  



 With the tool provided you can now check how much heat energy your current radiators can provide on water temperatures of 40 and 50c and/ or how big of a radiator you need to add or upgrade to in order to satisfy your heat loss for that room. (for this choose new installation option).

If the amount of wats your current radiators produce at water temperature of 50c matches or exceed wats needed for that room by your heat loss calculation, you don’t need to upgrade your radiators to have a heat pump. 

So, let’s say for example that we need 500 watts of heating energy in a room, measure the height of the radiator in meters and multiply it by its width. 

Assuming a type 22 radiator with dimensions of 600mm in height and 1200mm in width, we calculate the area by multiplying 0.6 by 1.2, resulting in 0.72m2. Plugging this value into our tool yields a power output of 1080 watts at a water temperature of 50 degrees Celsius. This surpasses the required 500 watts, indicating that your radiator can operate at an even lower temperature, ensuring a highly efficient system.

Now if you come up short you can use this tool to check how big of a radiator you actually need for this system: 
Choose new installation option in our tool and pick desired radiator type.

The tool will show you how wide of a radiator you need for three standard radiator heights (0.6, 0.8, and 0.9m) in order to satisfy your heat loss for flow temperatures of 40 and 50c.

This way you can plan and check if the radiator will fit in your desired place or if maybe you need to split it into two smaller ones or even pick a different height since taller radiators will be narrower and vice versa.

Note: There are radiators that are out of standard proportions for exceptions cases, consult your preferred radiator manufacturer in order to find what radiator will suit your needs considering your heat loss demand.

Play around with this tool to check what suits your needs the most.

Do I need to upgrade my pipework? 

Another common misconception is that heat pumps require large 28mm pipes or even wider. 

Heat pumps do require a greater flow rate, that is true and usually you need larger diameter pipes to achieve that. 

But as you will see below, your current pipework is most likely sufficient and if not, there is a workaround for that too. 

Pipe size does not influence the flow temperature; rather, it depends on the required flow rate and the amount of energy needed to be transported through the pipes.


The only variable that affects this is your system ΔT so let’s tackle that first. 

What is system ΔT: 

The system ΔT is the temperature difference between flow and return pipes (similar to ΔT mentioned above between indoor and outdoor temperatures). 

For the heat pumps we want to aim for temperature drop or temperature difference between flow and return of 5C, range between 5-7c is acceptable but 5c is the best spot. 

To put things in perspective a gas boiler has a temperature drop of ΔT 20 which means that boiler has to increase water temperature by 20 upon return. 

If we want to narrow this ΔT from 20C to 5C to be heat pump ready, we need 4x faster flow rate and thus 4x larger bore pipes, right? Well not exactly..

Is my existing pipework ready for a heat pump? 

First when we are talking about pipe diameter, we are talking about primary pipe work. Primary pipework is just the main pipework that goes from your boiler/heat pump before it tees off to the rest of the system

In older homes existing pipework is most likely designed for system ΔT of 11 which already brings us much closer to desired ΔT of 5-7C. 

Now considering we already calculated complete heat loss for our property we already know how much energy (wats) we need to move around through our pipes. 

While theoretically, you can augment power transmission in a pipe by accelerating water flow, this can lead to problems such as erosion corrosion, noise, and, crucially, turbulence. Excessive resistance due to turbulence can impede the required flow, rendering the system ineffective.

Remember this will most likely affect only our primary pipe work so if we replace our current 22mm pipe to 28m from the heat pump to where it tees into the rest of the system, we should be good to go. 

Now we just need to check if both pipes that are splitting from our 28mm primary pipe can carry the amount of energy needed to our rooms.

Optimizing Pipework and Considering Future Updates:

Note: In the future we might update our tool so that you can calculate the amount of energy you can move through your existing pipework on different flow speeds while maintaining desired flow ΔT. We decided not to because we deemed it not necessary as through our research, we found out that 90% of properties has sufficient pipework with exception of replacing only primary pipes which is usually not to expensive due to a short length those pipes need to travel.

If the pipes are smaller, such as 22mm or less, they probably cannot transport the necessary energy to meet our heat loss requirements. In such cases, upgrading these pipes becomes necessary, and the cost of such upgrades can be significant.

This brings us to our “workaround” that I mentioned previously.

Hydraulic separation:

Hydraulic separation comes in the form of a close-coupled tee, a low loss header, and a buffer or plate heat ex-changer.

It provides a ‘hydraulic break’, so the heat pump only needs to pump water to hydraulic separator with as much flow rate as heat pump needs and you will have additional water pump or more depending on number of heating circuits your property has, after the separator to feed your radiators.  

Hydraulic Separator


Bear in mind that even thou heat pump now has enough flow rate required to maintain ΔT 5, this separation will most likely cause heat pump to run hotter than it usually needs because of the differences between flow rates on both sides of hydraulic separator and your COP will be lower. 

The one form of hydraulic separation people talks a lot about are buffers:

A buffer tank is simply an insulated vessel that adds additional volume of hot water to your heating system, and it acts a little like a battery for the heating system. 

Aside from contributing volume to the system, which is typically adequate, I perceive minimal utility for buffer tanks in heat pump-driven systems. This is because the compressor inverter technology employed in contemporary heat pumps comprises advanced drive modules that facilitate variable speed operation. Because inverter technology has variable speeds—as opposed to the basic on/off functionality of single-stage and two-stage units—it allows you to cool or heat your home based on the specific requirements of your space. This will be important in our next article. 

So basically, engineers see hydraulic separation as more of a compromise and i would agree. 

You should already have well insulated property if you are planning to switch to a heat pump but if not than you should definitely invest in your insulation rather your pipe work. 

This way you will get two flies with one blow, you will drastically lower your heat loss or amount of energy you need to keep your property warm, thus making your current pipe work sufficient and reduce your flow temperature drastically which we know by now will increase your COP. 


So does heat pumps work? The answer is yes, but as we see in our little article here it requires a lot of planning and system design in order to make them work and not mentioning the positive impact they have on our environment. Some people are switching to heat pumps from gas boilers with no additional efficiency but only to de-carbonize their homes which i applaud.  

Also a lot of governments are issuing returns upon switching to a heat pump from a fossil fuel heaters so check if there are some benefits of de-carbonizing your home in this manner with your local government.  

There will be more articles like this one guiding you on how to set up your heat pump after installation since that part is equally important as system design.  

If you are just building your property then the logical choice would be underfloor heating with heat pump which is so incredibly efficient and pleasant.   

Please choose your installers carefully, luckily now by using the knowledge you obtained here you can challenge them and recognize true engineers from sellers.  

Also make sure to follow manufactures clearances while choosing the position for the outside unit. 

Scroll to Top