Combi boiler for a large house

 

Looking for a combi boiler for a large house? Here we go through the issues that you need to consider when selecting the best combi boiler for a large house to suit your requirements. Selecting the correct combi boiler size for any home, is critical, especially when your residence is a large house, with multiple radiators, or an underfloor heating system and multiple bathrooms, it then becomes vitally important if you require a high efficiency and economical boiler with exceptional hot water flow rates then we have the perfect high heating efficiency gas boilers for your large house / home/ property, which can be fired with either natural gas or LPG / Propane gas.

In a nutshell combi boilers heat water for the central heating system and hot water demands,without a storage hot water cylinder. For this reason, they can struggle to cope with high hot water demands of multiple bathrooms properties that you might have in a 4 or 5 bedroom house for example. But we have a solution to this issue with the best combi boilers for a large property -please read on

What are combi boilers, and what do they do ?

Firstly, we need to establish what a combi boiler is. Well, the boiler’s official name is a “combination boiler” – but over the years the word has been shortened just to “combi boiler”. These boilers are now the most popular type of boiler for homes, flats, etc. in the residential market in the UK. A combi boiler not only supplies the heat for the central heating of the home (i.e., central heating system), but also heats the domestic hot water demands instantaneously as a hot water tap is opened.

If you already have a regular boiler installed in your property, that is coupled up with a hot water storage cylinder that requires a cold water tank in the loft space (if the hot water storage cylinder is a vented cylinder), then installing a combi boiler means you no longer need this cold water tank anymore and recover some loft space.

Generally combi boilers need to be more powerful than regular and system boilers to do the same job, as they use a hot water cylinder to store hot water.

Another benefit of a large combi boiler is that the hot water is fed from the mains water supply, eliminating the need for a feed and expansion tank, and thus the water pressure is often higher, resulting in better hot water performance and higher energy efficiency, without the need to store hot water in an unvented cylinder, for example.

These factors make a combination boiler one of the highest efficiency boilers on the market, with an attractive low cost purchasing price, along with the lower installation costs and continual lower running costs than the older type system boilers that were extensively used with hot water cylinders in previous times in larger homes or properties with complex heating systems.

There are two main elements to a combi boiler sizing, which need to be considered when selecting the correct size large house combi boiler –

1. The central heating side of the boiler– You need to establish how much of a heating load or requirement your large property will have. This is to ensure that our energy efficient boiler has sufficient capacity to heat your large home.

2. The Domestic Hot Water performance – This is the hot water that you use to bath, wash or do the dishes/kitchen use – when preparing meals etc., as you’re not storing hot water in a separate hot water tank with a combi boiler, which makes them the most efficient boilers.

We will look at both of  these issues and give you the guidance to ensure that you have the best solution for your combi for a larger house or property with multiple bathrooms and high hot water demands.

Combi sizing for large house / homes / properties

The first part is the easier bit, as they say. It doesn’t matter what heat emitters you are using to heat your home, whether it be a radiator system or an underfloor heating system or even a combination of both. The principle of heat loss sizing for your property doesn’t change for conventional boilers or combi boilers, or if they’re gas and oil boilers for your heating requirements. 

Basically, the fabric of your home loses heat, depending on how well insulated the building materials used, such as the brickwork, the floor and the roof. This is known as the “U “value of the materials in question.

This” U “value is official expressed as the rate in Watts [W]) at which heat transfers through 1 square metre [m²] of the surface of a buildings material when there is a temperature difference of 1ºC between the internal and external environments.

So, if you have a property built from the late 1990’s onwards then you are safe to use this ready reckoner chart. This ready reckoner table is based on a brick and block cavity wall with mineral wool insulation having a total wall thickness of 312 mm has a “U” value of 0.3 W/mtr. The building regulation from the late 1990’s specify that this “U” value must be achieved, to pass the building regulations.

You need to ensure that you have the total floor area of your home, including the ground level, 1^st floor, 2^nd floor etc. It is the home’s / properties total floor area you need to calculate.

Power Output of Boiler	Heating area with Height of 2.7 Mtrs & U Value of 0.3
4.5 kW	~ 55 Mtrs/2
7.5 kW	~ 85 Mtrs/2
9 kW	~ 110 Mtrs/2
13.5 kW	~ 165 Mtrs/2
15 kW	~ 180 Mtrs/2
22.5 kW	~ 278 Mtrs/2
24 kW	~ 300 Mtrs/2

For example – If your 5 bedroom house or large home has a total floor area of 600 M/2, then you’re going to need a 48 kW Combi boiler (2 x 300 m2 = 2 x 24 kW – thus a 48kW output combi boiler)

If your total floor area is 440 M/2, then you’re going to need a 48 kW Combi (1 x 300 m2 =  24 kW  and 1 x 165 M2 = 13.5 Kw –always go up on the chart – you can turn a combi boiler’s power output down , if you have it there , but you can never turn it up , if it doesn’t have the capacity – thus 24kw + 13.5 Kw = 37.5 kW  total boiler output

How many radiators ?

Radiators come in various kW outputs. Ultimately, the number of radiators will depend on what is required to cover your property’s kW heating load requirement.

The best combi boiler is a modulating boiler

Our combi boilers for large homes are modulating boilers, which means they will automatically ramp up and down the boiler’s power to suit the central heating (radiator or underfloor) requirements. They are very clever combi boilers these days!

Domestic hot water performance of the boilers

Ok, now for the second part of a large house combi boiler – the domestic hot water performance/sizing – and these days this is the most important factor when selecting the best boiler to suit your requirements.

Hot water flow rates

A standard showerhead typically requires 7 to 8 litres of hot water per minute of water at 40C, while “green band” showerheads that meet the European Water Label’s criteria demand only 6 litres per minute. Think of this standard as an “ErP” rating for hot water bathroom products, taps, etc. for domestic properties.

 

Please be aware that drench showers can have some huge flow rates, from 15 litres to pretty much any flow rate – 30 litres per minute is not uncommon.

 

 

Kitchen sink taps—4 to 6 litres per minute.

Sink taps, which are the standard type, have a flow rate of 4 litres per minute.

Basin/cloakroom “spray taps”—2 litres per minute— these water-saving spray taps are very popular now, as they save water and energy requirements.

Bath mixer taps – modern bath taps have an approximate demand rate of 12 litres per minute.

So by adding all your potential hot water outlets and then applying a diversity factor (a factor that not all the hot water outlets will be used at the same time), you can calculate your hot water demand for your large house combi boiler.

Combination boilers for large houses product range

Combination boilers use a plate heat exchanger to heat the domestic hot water up to temperature from the “heating water side of the boiler”. They have benefits in that they only heat the hot water when there are hot water demands; thus, they are a highly efficient boiler, and we do a range of this type of combi boiler up to 100 kW of output.

50kW Combination boiler – the best combi boiler for a 4 bedroom house ?

A 50kW combination boiler – whereby the plate heat exchanger is integral to the casing of the boiler. This boiler is a modulating boiler with a heating power range of 5.29 to 53.40 kW output at 50/30°C flow and return or 4.83 to 49.19 kW at 80/60°C with 20.30 litres/min of domestic hot water with a temperature rise of 35 degrees C (the standard temperature rise for Scotland and Northern Ireland locations in wintertime conditions) or a 23.4 litres/min hot water flow rate with a 30°C temperature rise. This 30°C temperature rise is the standard temperature rise for most of the UK in wintertime conditions.

This boiler which is an “A”-rated boiler for the heating system and hot water.These are fully detailed on this dedicated webpage 50kw combi boilers which shows dimensions, performance etc. This boiler will be the best combi boiler for 4 bed 2 bathroom house in 99% of the time or a four bed house with 1 bathroom, but using a drench shower.

 

 

If you want the best combi boiler for 4 bed 3 bathroom house, then you’re probably going to need our larger models, detailed below.

Larger output gas combination boilers 

We also have a 60 kW, 75 kW, or 100 kW output option for a large house combi boiler which makes these powerful combination boilers especially suitable for even larger homes such as a combi boiler for 5 bedroom house, that usually have larger hot water demands via multiple bathroom or showers, that any gas safe registered engineer can install.With these models, the plate heat exchanger is mounted directly underneath the boiler above the low loss header (picture below).

 

 

DHW heat exchanger 

The 60 kW model, this combination boiler is a modulating boiler with a power range of 6.44 to 62.84 kW heat output at 50/30°C flow and return or 5.75 to 57.82 kW at 80/60°C with 28.83 litres/min of domestic hot water with a temperature rise of 30 degrees C.

These can either be wall-hung boilers or floor-standing boilers when using our frame mounting kit, as seen in the picture above.

The 70 kW model, this combination boiler is a modulating boiler with a power range of 3.87 to 79.35 kW heat output at 50/30°C flow and return or 3.5 to 72.83 kW at 80/60°C with 35 litres/min of domestic hot water with a temperature rise of 30 degrees C.

These can either be wall-hung boilers or floor-standing boilers when using our frame mounting kit, as seen in the picture above.

The 100 kW model – again, this commercial boiler is a modulating boiler with a power range of 5.29 to 106.80 kW heat output at 50/30°C flow and return or 4.83 to 98.37 kW at 80/60°C with 47.28 litres/min of domestic hot water with a temperature rise of 30 degrees C.

These can either be wall-hung boilers or floor-standing boilers when using our frame mounting kit as above in the picture.

The 75kW and 100kW large house combi boiler models mentioned above have a modulation ratio of 1:20 for greater efficiency and reduced consumption both in heating and in DHW production, whilt the 60kW has a 1:10 modualtion. Not only do these units have stainless steel heat exchangers as standard, but they actually have two heat exchangers, or boilers, as such within one casing, meaning should one fail, you still have 50% of your duty available to you (the 60kW boiler only has one heat exchanger). Another benefit is that you can service one boiler while the other is working, so there will never be any “downtime” for your heating or hot water systems, which is a great feature!

Cold water mains supply – Why it’s vital

Combination boilers also have a minus point, which really come into factor when trying to fulfil the hot water demands when used in larger homes with multiple bathrooms or many hot water taps.

A combination boiler may struggle to meet high demands for hot water because it draws all of its water supply directly from the mains water supply. An example of this is when multiple hot water taps are turned on in various bathrooms, the kitchen or other rooms within the house; you will often see a dramatic reduction in the water pressure. That’s why the flow rate of the cold water mains should match your potential hot water requirements.

Hot water cylinder ?

This is caused by the combination boiler not having the benefit of a storage hot water tank, which would meet these levels of demand. This situation used to be resolved by using a regular boiler type commonly known as gas system boilers in conjunction with an indirect hot water storage cylinder.

System boiler for a large house

We have a full range of system boilers that are used in conjunction with a hot water storage cylinder / hot water storage tank when the hot water demands of multiple bathrooms require you to store hot water when the hot water outlets demands of multiple bathrooms can’t be satisfied by the cold water mains supply that combination boilers for large houses rely on.

Obviously installation costs are more for a system boiler and an unvented hot water cylinder setup, as they are more complex heating systems with more pipe work required, but high hot water demands sometimes require this.

Control options for the boilers

Everyone now wants to be able to control their boiler, when they are out and about, be it travelling or at work or even on a plane – having the facility to turn your boiler on and have the house warm for when you return to it has now become almost standard. Well the good news is that a combi boiler can do this – they have a control panel is also what is called “OpenTherm Plus “compatible, which means you can control these combi boilers, via the use of an “OpenTherm” controller, such as a “nest” type or similar.

This means you can make your life simpler and control these combination boilers from either your mobile phone (android or apple) your PC or tablet, from anywhere in the world, as long as you have an internet connection.

The control panel on these combi boilers also has numerous inbuilt features such as –

• Frost Protection – Full protection against freezing of the heating and domestic hot water in low ambient temperatures
• Pump Protection system – Anti-blockage System -The circulation pump is activated automatically once every 24 hours and prevent any blockage
• Ability to operate according to different heat demands with the variable flow pump control
• Low fuel consumption and fixed combustion efficiency thanks to the PWM driver, high modulating fan and high modulating gas valve
• Ability to operate according to different heating system configurations

Heating engineers

The last point is that all combi boilers with gas fuel types should be installed by a Gas Safe registered engineer, not just a heating engineer, to comply with the regulations and to ensure that the combi boilers are safely and correctly installed.

Hot water cylinder ?

This is caused by the combination boiler not having the benefit of a storage hot water tank, which would meet these levels of demand. This situation used to be resolved by using a regular boiler commonly known as system boilers in conjunction with a hot water storage cylinder.

System boiler for a large house

We have a full range of system boilers that are used in conjunction with a hot water storage cylinder / hot water storage tank when the hot water demands of multiple bathrooms require you to store hot water when the hot water outlets demands of multiple bathrooms can’t be satisfied by the cold water mains supply that the biggest combi boiler relies on.

Obviously installation costs are more for a system boiler and an indirect unvented hot water cylinder setup, as they are more complex heating systems with more pipe work required, but high hot water demands sometimes require this.

What are you waiting for ! Call us, for the best combination boiler for large properties

So should you be looking for a combi boiler for a large 4 bed house or for a 5 bedroom house , with 2 , 3 or even 4 bathrooms , you can now see why our combi boiler is the best option , as the element of some hot water storage , which is as small as possible , and thus saving on wasted energy , but large enough to cope with the hot water requirements of a large home or property, then please don’t hesitate to contact us at Flexiheat UK for the best combi boilers prices, using the contact us email , or alternatively give us a call on 01202 822221. As we believe we have the best combi boilers for large houses for sale on the UK and Irish market.