Underfloor Heating (UFH) with a Heat Pump

Why use UFH with a heat pump?

UFH is one of the few heating systems that are a perfect partner for use with Heat Pumps. In case you are wondering, wall and ceiling heating systems are two of the others (which we also supply). The main reason these systems are great for heat pumps is down to the flow temperatures these systems use when compared to traditional radiator systems. 

Heat pumps are intended to be run at low temperatures, much lower than boilers. For example, a boiler is usually producing a flow temperature of around 70-80ºC for radiator systems and around 50-55ºC for UFH systems. All heat pump manufacturers produce energy efficiency data for their appliances and in almost all cases, this data shows that the flow temperature (or MWT, mean water temperature – average of the flow and return, for example 37.5ºC flow and 32.5ºC return) is 35ºC. With an air source heat pump, the data is also based on a 7ºC outside air temperature. To achieve the low flow temperature with radiators requires them to be at least 50% bigger than they would be with a boiler based system – unless the heat pump is run a lot higher e.g., 55ºC, which will have a very detrimental effect on the efficiency of the heat pump. 

Our Variotherm Wall and Ceiling systems are also designed to be used at 35ºC with heat pumps.

Designing and Installing the UFH.

We design UFH differently for heat pumps than we do with boiler-based systems. As the flow temperature for heat pump use is much lower, we need to increase the surface area / coverage of UFH pipe. As a general rule, pipe spacing (the distance centre-to-centre of the pipe runs) for boiler-based systems is 200mm, but with heat pumps we reduce the spacing to 100mm, effectively doubling the amount of pipe. The COP (coefficient of performance – how efficient a heat pump is of converting electric into heat) of a heat pump is based on the recommended flow temperature and installing the pipes at 200mm spacing would seriously reduce the COP.

Some UFH and heat pump suppliers will design and install pipe at 150mm and whilst there are examples where this will not harm efficiency e.g. a very well insulated property, tiled floors, having pipe installed at 100mm will always give better efficiency and a better output from the UFH. At VarioHeat, we will only design and/or install at 150mm pipe spacing if we have a written request to do so (but we will also politely recommend 100mm!)

Some of our systems, such as the VarioComp overfloor/retrofit system, is only supplied at 100mm spacing irrespective of the heat source. Using UFH at 100mm spacing with a boiler will also enable the boiler to run at low temperatures, improving efficiency and output.

Considering a Heat Pump in the future?

We have many customers who have a boiler at the time of their property build/renovation but who will comment that a heat pump is going to be a consideration in the future. What we offer in these cases is to ‘future proof’ the property/UFH system, by recommending that the UFH is designed and installed for the heat pump use now.

There are two big advantages of this (and one slight disadvantage):

  1. Having much more pipe than normal for a boiler will provide faster heat-up time and create more residual heat. 
  2. With the faster response times and lower running temperature, around 15ºC-20ºC less, therefore the boiler will be more efficient. It will not require as much energy to heat the water and will not be on for as long.

The slight disadvantage to having pipe at 100mm spacing at this stage is that the UFH equipment and installation will a bit more. From our experience this is usually around 20%-35% more, however we feel that the gains in efficiency and comfort plus the ‘future proofing’ of the property far outweigh the initial higher cost.

UFH Controls with Heat Pump use

For multi-zone UFH with a boiler, it is usually most efficient to have separate thermostats for each area (or each main area combined, e.g. bedroom and ensuite together) so that the UFH is only used where it’s required throughout the day/night. The thermostats are used as a ‘call for heat’ function. At VarioHeat, we recommend that thermostats are set to 18ºC to 20ºC as this gives a comfort level that the vast majority of people will enjoy but if they’d like their rooms to be warmer, there is unlikely to be much more than a couple of degrees required.

When it comes to heat pumps, the manufacturers and installers will often recommend that the UFH is predominantly ‘open-loop’ with limited control. What this means is that all circuits are fed/open and the only controls fitted are in bedrooms and the kitchen to temperature limit, rather than call for heat. In addition to this, they will likely use weather compensation to control the flow temperature and when it is provided to the UFH. In short, the heating is used slow and low in this case.

Traditionally, for boiler use, we need to supply a thermostatic mixing valve and pump set for the manifold. When it comes to a heat pump system, the flow temperature is controlled at source and the overall system is usually centrally pumped so there’s no need for either component at the manifold(s). There are some examples where one or both are used and at VarioHeat, we like to talk to our customers and their installers so that we can ascertain what the needs of the project are.

If you would like to discuss this article, have some questions of your own or would like to discuss your project then please don’t hesitate to get in touch.

VarioHeat Ltd
Unit 5 Tanshelf Industrial Estate
Colonel’s Walk 
Pontefract
WF8 4PJ
01977 798720
damien@varioheat.co.uk

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Testimonials

We have had an exceptional experience with Damian at Varioheat during our underfloor heating journey. His attention to detail with our complicated layout has been impeccable. He has consistently gone above and beyond to assist us, ensuring everything is perfectly tailored to our needs. The process couldn’t have been easier. Highly recommended!

Leanne Broadhurst

Damien did a fantastic job of installing underfloor heating for us. He was reliable, on time and the work was completed to a high standard. I’d recommend Damien in the highest terms.

Elliot Kay

When downsizing, we chose to replace our radiators with underfloor heating. Damien, recommended by friends, conducted a thorough survey and provided expert advice. His knowledge and the detailed pipe layout drawings he supplied were crucial for our DIY installation.

Damien was incredibly supportive throughout, from initial design to commissioning. The system, which covers our entire ground floor with 320m of pipe, is quiet, efficient, and comfortable. We highly recommend Damien and VarioHeat for anyone considering underfloor heating.

Bill Grant

…….The heating system is quiet, efficient and comfortable and I would strongly recommend Damien and Varioheat to anyone considering underfloor heating.

Bill Grant

Having enjoyed underfloor heating in a previous home, I knew I wanted it in my new house. After seeking recommendations, I contacted Damien to install it throughout the house. I’m thrilled with the results. Damien was helpful, friendly, and thorough, explaining everything clearly and working hard to complete the installation promptly. I highly recommend both underfloor heating and Damien’s services.

Lucy Clark