Searching for the best combi boiler?

You’ve probably hear that combi boilers are more compact and energy efficient than traditional boilers. But given there are so many different combi boilers on the market, which one is right for your specific needs?

Well, we’re here to help.

We’ve selected and reviewed the 6 best combi boilers on the market. We’ve also answered some of the most common questions people have about combi boilers.

So let’s get right to it!

In A Rush? Here’s Our Top Three Picks

Top 6 Best Combi Boilers

We selected all these combi boilers based on the following criteria:

• Energy Star certification: Energy Star® certified appliances consume 10% to 50% less energy than those that aren’t. Their energy savings will be even higher if you’re replacing an old appliance with one that is Energy Star® certified.

• Extended warranty: The vast majority of the combi boilers we’ve reviewed below provide a 10+ year warranty on their heat exchangers, a 5-year warranty on their parts and a 12-months warranty on labor cost. 

• 4GPM+ hot water flow rate: Boilers offering a flowrate of more than 4GPM can easily meet the hot water requirements of a small-sized household with up to 2 bathrooms, 1 to 2 bedrooms and up to 10 radiators.

• Stainless steel heat exchanger: Stainless steel heat exchangers conduct heat faster than aluminum or carbon steel heat exchangers, saving energy. They also have higher temperature tolerance and resist corrosion better, which enhances their shelf-life.

Noritz CB199-DV-NG Combi Boiler

• Weight: 95 pounds
• Type: Natural Gas
• Max Flow Rate: 9.2 GPM
• Warranty: 10 years heat exchanger/5 years parts

Do you regularly run out of hot water?

Have a large house whose hot water requirements can’t be met by an average-size combi boiler? Then you must check out the Noritz CB199. And not only because its massive 9.2 GPM flow rate allows it to meet the hot water needs of a family of 10. 

It’s 95% energy efficient and reduces your yearly outlays on natural gas by as much as $300 if you’re currently paying more than $1,000 a year in heating bills. Its Energy Star® rating means appliances consume up to 50% less energy than non-Energy Star® rated products.

The boiler’s hot water output is enough to meet the requirements of 4 or more bathrooms, multiple dishwashers and washing machines, and 3+ showers. Though it would be best if you don’t use it to get a power shower as the unit doesn’t have any pump to raise its water pressure.

The Noritz CB199 is part of its brand’s ‘CB’ series whose products are famous for:

a) compact dimensions

b) utility for areas that experience the harshest of winters.

As a result, it occupies 80% less space than other combi boilers while meeting space heating and hot water needs of large households.

That doesn’t mean that everything about this product is excellent. Its water pressure is nowhere near enough to supply a power shower without the installation of a pump. And despite its compact dimensions, this unit is heavy.

Things We Like:  

• Massive 9.2GPM flow rate
• Energy Star rating
• Compact dimensions
• 10-year heat exchanger warranty

Things We Don’t Like:      

• Massive weight
• Poor water pressure

How It Compares With Our Criteria

1. Energy Star certification®: Yes
2. Extended Warranty: Yes
3. Stainless steel heat exchanger: Yes
4. 4GPM or more flow rate: Yes

Best Gas Combi Boiler

Rinnai HTG DHW Combi Boiler

• Weight: 70 pounds
• Type: Natural Gas
• Max Flow Rate: 4.2 GPM
• Warranty: 12 years heat exchanger/2 years parts/1-year labor

Multiple features make the Rinnai HTG DHW one of the best on the market.

It is equipped with a stainless steel heat exchanger that can resist corrosion and withstand high temperatures. The exchanger is coated with a copper nickel integrated plate that enhances its durability even further.

Unlike the Noritz CB199, the Rinnai Boiler can be used to supply water to a power shower. That’s because it comes with an integrated modulating pump that raises its pressure to a level at which its hot water supply could match or even exceed the demands of a power shower.

Another area where this model distinguishes itself from the Noritz CB199 is venting. The CB199 just gives you one venting option – requiring you to use the VK3-H-PVC to exhaust its flue gases. This model, however, gives you eight venting options to choose from.

Our favorite among them is the polypropylene venting option..

Apart from being lightweight than the stainless steel venting option (included), polypropylene pipes cost less than PVC, CPV, and two-pipe systems. And the best thing about this venting option? It’s a cinch to install.

While a great option, this combi boiler suffers from its fair share of drawbacks. Its hot water supply (up to 4 gallons per minute) is only suitable to meet the needs of a household of 4, even though it costs more than the the Noritz CB199.

Things We Like:  

• Eight venting options
• Integrated modulating pump
• 12-year heat exchanger warranty

Things We Don’t Like:      

• Pricey
• Relatively low hot water flow rate

How It Compares With Our Criteria

1. Energy Star® certification: Yes
2. Extended Warranty: Yes
3. Stainless steel heat exchanger: Yes
4. 4GPM or more flow rate: Yes

HEATLINE by Vaillant Combi Boiler

• Weight: 73 pounds
• Type: Natural Gas
• Max Flow Rate: 10 GPM
• Warranty: 2 years

No products found.

How does this model compare with the two we reviewed above?

Start by comparing the flow rates. The Noritz CB199 and Rinnai Boiler can churn out 9.8 GPM and 4.0 GPM of hot water, respectively.

This model outperforms both with its massive 10 GPM flow rate. That means you can rely on it to meet the hot water needs of a small-size restaurant.

Then comes its heat exchanger.

While both the top two models have a stainless steel heat exchanger protected by the DHW plate, this model’s heat exchanger is made of aluminum, which doesn’t perform as well as stainless steel when it comes to keeping rust and corrosion at bay.

One would imagine that’s the reason why the Capriz 2’s warranty is smaller than its two counterparts reviewed above. Both those models are warrantied for 10+ years. In contrast, the Capriz 2 has a subpar 2-year warranty on its heat exchanger, parts, and labor.

All these factors shouldn’t come as a surprise given that this product costs almost 5x less than Noritz CB199 and almost 6x less than the Rinnai HUG Boiler. Despite all of that, it still packs decent features like a temperature control system, vertical and horizontal flue kits, and an analog timer.

Things We Like:  

• Competitive asking price
• Horizontal and vertical flue kits
• Massive 10 gallons per minute flow rate

Things We Don’t Like:      

• Small warranty

How It Compares With Our Criteria

1. Energy Star® certification: Yes
2. Extended Warranty: No
3. Stainless steel heat exchanger: Yes
4. 4GPM or more flow rate: Yes

Worcester 25i Combi Boiler

• Weight: 31.7 pounds
• Type: Natural Gas
• Max Flow Rate: 2.7GPM
• Warranty: 5 years heat exchanger/10 years parts and labor

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What is it that sets apart the Worcester 25i from its predecessor, the 24i junior?

The 25i features an improved output – with both its DHW kW and flowrate up from 24kW and 8.6l/m to 25kW and 9l/m. This allows it to deliver a quicker hot water output and better heating performance.

The Worcester 25i also has a much-improved interface.

Gone are the knobs and buttons that made the 24i’s control panel look ugly. They’ve been replaced by a scrolling text display that lets you chat more easily with Worcester’s in-house engineers when diagnosing any issues.

The Worcester 25i also saves you from buying additional equipment that could fight frozen condensate. It is equipped with a built-in siphon, an item that protects its pressure sensor from the potentially disastrous effects of quick-fire pressure changes.

Certain components of the Worcester 25i, including its heat exchanger, are much easier to service. It is also compatible with Worcester’s Comfort Controls that let you program hot water and heating.

You can also control its operation using the Worcester Wave.

It is a smart thermostat that allows you to control this boiler’s operation from a smart device. All you have to do is to install its app on your device, pair it with the boiler, and control this boiler’s heating performance and hot water output from anywhere in the world, with internet access.

The only thing about this boiler that disappointed us was its warranty. Whereas the top picks in this review offer 10 year+ warranties on their heat exchangers, the Worcester 25i, despite being UK’s top-selling combi boiler, takes responsibility for its heat exchanger for only five years.

Things We Like:   

• Compatible with Worcester’s Comfort Controls
• Can be controlled using a smart thermostat
• User-friendly and neat control panel

Things We Don’t Like:      

• Only 5-year warranty on heat exchanger

How It Compares With Our Criteria

1. Energy Star® certification: Yes
2. Extended Warranty: Yes
3. Stainless steel heat exchanger: Yes
4. 4GPM or more flow rate: No
   

Rinnai M060SN Combi Boiler

• Weight: 82.3 pounds
• Type: Natural Gas
• Max Flow Rate: 9+ GPM
• Warranty: 12 years heat exchanger/2 years parts/1-year labor

One problem users face with natural gas boilers is deciding where to install them. The Rinnai M060SN solves it by offering multiple venting options such as PVC, CPVC, two-pipe systems, among others, thereby letting you set up this unit wherever you like.

Another issue that plagues the performance of gas boilers is their heat exchanger catching rust and corrosion. This problem mainly arises due to a poor quality material used in the exchanger’s construction. Rinnai MO60SN has prevented it by equipping this boiler with a stainless steel heat exchanger.

This product won’t send your natural gas bills through the roof either. That’s because it’s Energy Star® certified and enjoys a 95% Annual Fuel Utilization Efficiency (AFUE).

Users living in areas where the natural gas supply is shaky can easily convert this model to run it on liquid propane. The kit required for the conversion is included in this package. And an outdoor reset sensor will turn off the unit if its internal pressure exceeds a safe limit.

There’s one issue with this boiler that might prevent users from buying it. Two of the items needed for its installation (one zone controller and two additional pumps) aren’t included in the package. You’d thus have to purchase them separately to get this unit up and running.

Things We Like:   

• Eight venting options
• Liquid Propane conversion kit included
• Energy Star certified and AFUE rated

Things We Don’t Like:      

• Package lacks some items needed for installation

How It Compares With Our Criteria

1. Energy Star® certification: Yes
2. Extended Warranty: Yes
3. Stainless steel heat exchanger: Yes
4. 4GPM or more flow rate: Yes

Noritz NRCB199DV-LP Combi Boiler

• Weight: 95 pounds
• Type: Liquid propane
• Max Flow Rate: 11 GPM
• Warranty: 12 years heat exchanger/5 years parts/1-year labor

Most combi boilers you see on the market aren’t easy to install. The Noritz NRCB199DV is different. It comes with a wall mount bracket to help any qualified mechanic get it up and running within hours. The frame also provides multiple mounting possibilities and saves floor space too.

Another thing that sets it apart from its competitors is the use of stainless steel.

The majority of boilers we reviewed above also used stainless steel for the main heat exchanger, but they used other materials for the plate heat exchanger. The NRCB199 uses stainless steel for its primary heat exchangers and the third flat plate heat exchanger, thereby ensuring all three last longer.

This combi boiler also has manageable running costs.

Mainly because it’s 95% energy efficient and is certified by Energy Star® to keep its energy consumption to a minimum. But also because it has a user-friendly control panel that lets you decide exactly how much heating and hot water you want from it.

The fact that it runs on propane gives this model superiority over natural gas boilers.

While propane costs more than natural gas (per gallon), it burns more efficiently. One cubic foot of natural gas provides 1,030 BTUs, while one cubic foot of propane offers 2,516 BTUs. That means you’d have to burn 2.5x more natural gas than propane to heat the same amount of water.

Even if you prefer the carefree supply of natural gas through pipes over the manual labor of refilling a propane tank, there’s no reason why you shouldn’t consider this boiler. It comes with a natural gas conversion kit using which any expert can easily switch it from one fuel to the other.

Having said that, this product might not suit you if you don’t have the space to install it indoors. That’s because it isn’t outdoor approved, which means it cannot be installed in an environment where it would be exposed to external elements and conditions.

Things We Like:  

• Natural gas conversion kit
• Energy Star® rated
• 95% energy efficient

Things We Don’t Like:     

• Cannot be installed outdoors

How It Compares With Our Criteria

1. Energy Star® certification: Yes
2. Extended Warranty: Yes
3. Stainless steel heat exchanger: Yes
4. 4GPM or more flow rate: Yes

Benefits of Combi Boilers

You can expect various benefits from having a combi boiler offering hot water and central heating to your home. They include higher energy efficiency, hassle-free installation, trouble-free maintenance, and more. Here are the top benefits of your ideal combi boiler:

High Energy Efficiency

According to one estimate, all modern combi boilers are more than 90% efficient. That means they convert more than nine-tenths of the power they receive into heat.

That is precisely the reason why they could reduce your energy bill while also keeping your carbon footprint in check.

Here’s why combi boilers are incredibly energy efficient. They heat water directly in the mains and don’t require a hot water cylinder or cold water storage tank. This allows them to get rid of energy losses that both these items cause in conventional boilers.

Quality Heat Exchangers

The best combi boilers are equipped with stainless steel heat exchangers certified by Energy Star® for their low power consumption. These heat exchangers are responsible for converting power (natural gas, oil, or electricity) into heat to raise water temperature.

Water flows through these heat exchangers, heats up and then goes through a ‘flow’ pipe into the central heating system. That means that were it not for the heat exchanger’s quality, much of the power supplied to a combi boiler will be lost in the form of energy losses.

Advanced Electronics and Diagnostics

Almost all combi boilers boast advanced electronics and diagnostics. This makes them easy to use by giving their users complete control over the boiler’s operation. Advanced diagnostics, meanwhile, makes troubleshooting combi boilers simple.

Hassle-Free Installation

Combi boilers are extremely easy to install, operate and maintain. Mainly because they don’t need pipes to divert water from your mains to a cold water storage tank.

Instead, combi boilers heat cold water directly in the mains, making their installation relatively quick and inexpensive.

Inexpensive to Maintain

The main reason why combi boilers’ maintenance costs are low is that you have only one unit to maintain. There are no external pipes, no cold-water tank, and no hot water cylinder that you need to take care of. Their replacement parts are also cheap.   

Don’t Suffer from Pressure Issues

Combination boilers do not have to deal with pressure issues because they take water directly from the mains. This also allows them to remain well clear of air locks, an event when air is trapped in the pipes and prevents water from coming out of the fixtures.

Provide Safe Drinking Water

It is safe to drink warm water from combi boilers because they take water directly from the mains and don’t have any storage tank to keep it. This differentiates them from conventional boilers whose water isn’t safe to drink under any circumstances.

If you’re looking to learn more about condensation in boilers and why you may need a condensate neutralizer, read this article.

Relatively Clean Operation

Most central heating systems that use combi boilers are extremely easy to clean because they don’t have to deal with the massive build-up of sludge. That’s because these models do not store water in a tank, where it would be easier for it to accrue rust and debris.

Things to Consider when Buying a Combi Boiler

Combi boilers are an essential investment for those of you living in the cold climate area. It’s vital you must consider their various aspects before choosing one for your home. Here are multiple things you must consider to get the best combi boiler in 2021:

Type of Combi Boiler

Here are the three main types of combi boilers:

Natural Gas Combi Boiler

• PROS: Low running cost; cost less up front; extremely energy efficient
• CONS: Aren’t easy to install; aren’t environmentally friendly

The best natural gas combi boilers have low running costs, cost less upfront, and boast massive efficiencies. However, since they require venting to exhaust flue gases, they aren’t easy to install. They aren’t an environmentally friendly option too.

Electric Combi Boiler

• PROS: Operate quietly; require no ventilation; easy to maintain
• CONS: Bigger running cost than natural gas boilers

These units rely on a heating element to raise the temperature of cold water. When compared with gas combi boilers, they operate quietly, require no ventilation, and are relatively easy to maintain. Though their running costs are greater because one unit of electricity costs more than one unit of natural gas.

Oil Combi Boiler

• PROS: Work in remote locations
• CONS: Poor energy efficiency; have to be stored outside; running cost fluctuates

An oil combi boiler is the best choice for landlords whose property isn’t connected to the main grid. Unfortunately, that’s where their benefits end. Oil boilers are less efficient than the other two types, have to be stored outside and their running cost fluctuates with the market price of oil.

Combi Boiler Size

Make sure you select the correct size combi boiler based on your heating and hot water needs.

A combi boiler that’s too powerful may end up increasing your energy bills. At the same time, one that is too small might not be able to meet your hot water and heating requirements at all.

Here’s how you can choose the right size combi boiler for your household:

• Select a 24 – 27kW combi boiler if your home has 1-2 bedrooms, one bathroom, and up to 10 radiators
• Go for a 28-34kW combi boiler if your home has 2-3 bedrooms, an equal number of bathrooms and up to 15 radiators
• Choose a 35-42kW combi boiler if your home has 4+ bedrooms, three or more bathrooms and up to 20 radiators

Tip: Hire a heating and cooling professional to determine the correct boiler size for your home. These personnel rely on Air Conditioning Contractors of America (ACCA) Manual J to calculate the correct boiler size based on your home’s wall thickness, foundation, windows, air filtration, and more.

Sealed Vs Non-Sealed Combustion Boiler

Combi boilers are either sealed-combustion or non-sealed combustion.

You must purchase a sealed combustion unit because it will send flue gases outside and outside air into the burner. Sealed-combustion units don’t require a draft hood or damper as they suck outside air directly.

That isn’t the case with non-sealed combustion boilers. They waste a lot of energy by taking heated air out of the house for combustion before exhausting it. They might also pose health issues by releasing dangerous gases into your home.

Energy Efficiency

An annual fuel-utilization-efficiency (AFUE) score rates the efficiency of all boilers. It does that by comparing the boiler’s energy consumption with the useable heat it produces. Regulations require that all new combi boilers have an efficiency of more than 92%.

The higher the AFUE score of a boiler, the higher it will cost, but the lower the running cost. For instance, if you replace a boiler with an AFUE of 65% with another whose AFUE score is 90%, you’d end up saving more than $350 per year in energy bills, if you previously paid $1,300 per year for fuel bills.

Combi Boiler Warranty

Combi boilers with an extended warranty give you peace of mind that you’d have nothing to lose in case the boiler gives you issues.

Almost all combi boiler manufacturers equip their models with decent warranties. But the length and terms of the warranty may vary.

Here are the longest available warranties offered by well-known combi boiler brands:

• Ideal: 12 years
• ATAG: 14 years
• Vaillant: 10 years
• Viessmann: 10 years
• Worcester Bosch: 12 years

Pro Tip: Some manufacturers give you the option to extend the warranty on their combi boilers if you choose to get it installed by their certified heating engineer. So we suggest that you ask the manufacturer of your model whether they’re giving any such offer.

Combi Boiler Installation

Do not try to install the combi boiler yourself.

Leave it to the heating engineer certified by its manufacturer or any other expert. A poorly installed boiler can pose many dangers including gas leaks, damage to the boiler’s body and invalidation of the boiler’s warranty, among other issues.

Here’s what else you should do before the installation of a combi boiler:

1. Get quotes from three different professionals and ensure that all fees, including any call-out fees, are included
2. Don’t believe in figures given in headlines – ask the professionals to provide you with a written quote of the total installation fee, including labor charges
3. Make sure they’re offering a guarantee with their work. This will keep you safe should anything goes awry with the boiler installation.

Combi Boiler FAQ

Q: What is a Combi Boiler and how does it work?

A: A combi or ‘combination’ boiler combines a central heating system with a water heater. It works by heating water directly from the main line. When you turn on the tap, cold water enters the boiler and the heat exchanger raises its temperature. The hot water then leaves the boiler via the ‘flow pipe’.

You can control the temperature of hot water via a thermostat on the boiler’s body. Most combi boilers also have a small reserve of pre-heat water. They use it to provide hot water when you open a tap, while taking that time to heat more water.

Q: How to boost your combi boiler’s efficiency?

A: Follow these tips to enhance your combi boiler’s efficiency:

1. Insulate your walls and attic
2. Have your boiler regularly serviced by an expert
3. Caulk around windows to prevent heat from escaping
4. Install weather stripping around doors
5. Clean your chimney every few months
6. Regularly bleed your radiators to let trapped air escape
7. Insulate cooling system ducts in attics and crawl spaces
8. Ensure your ceiling fan runs clockwise to blow climbing heat down
9. Insulate your pipes with foam tubes to prevent heat loss
10. Run the boiler for at least 15 minutes/day in summer to keep things active

Q: What is the installation cost for combi boilers?

A: The installation cost for combi boilers ranges between $600 and $3,500, with the like-for-like models costing less. A more complex installation, which may involve installing a combi boiler in place of a different style of boiler, might set you back close to $3,500.

Q: How much does it cost to install a combi boiler and multiple radiators?

A: For an average 3 bedroom house, the total cost will be close to $5,000. At this cost, you’ll get one 28kW boiler and nine radiators. That cost excludes pipework, for which you’d need to add $1,300 on top if your combi boiler didn’t work with existing pipes.

Q: What is the best place to put my combi boiler?

A: Here are the most common places to put your combi boiler:

1. Kitchen: Most users choose to have their combi boiler installed inside their kitchen cupboard. That’s because combi boilers are pretty compact and are capable of being fitted into tight spaces.

• Utility Room: Make sure that no wires surround the boiler if you chose to put it away in the utility room. Otherwise, if you can’t make space, you might want your boiler installed somewhere else.

• Loft: Combi boilers put away in lofts won’t interfere or gobble up your living space. Though you’d need to have a ladder to access the boiler when the need arises. The area needs to have adequate lighting and must be boarded too.

• Airing Cupboard: Swapping your heat-only system with a combi boiler? Then you might want to put your combi boiler in the airing cupboard. Just make sure that the boiler doesn’t make much room, as your bedroom will be nearby.

Q: How is a combi boiler different from a traditional boiler?

A: Combi boilers are more compact, easier to install, and prone to fewer heat losses than traditional boilers. Even the worst combi boilers are more energy-efficient and, if appropriately insulated, will leak less heat to the surroundings than their traditional counterparts.

However, suppose you want to run more taps at once and looking for a boiler that could be retrofitted with your existing pipework. In that case, you may need to go for a traditional boiler. That’s because they have a bigger reserve of hot water.

Q: Is a combi boiler gas or electric?

A: Combi boilers can be run on electricity, natural gas and propane.

Electric combi boilers are easier to install because they don’t require venting. Natural gas models have a low running cost and cost less upfront too. Propane boilers, meanwhile, have the lowest running price of the three.

Q: Does a combi boiler add value to a house?

A: According to research by comparison site GoCompare, a new boiler costing $2,700 will add at least $11,000 to the value of a house. That means that if you add a combi boiler to your home today, you can expect to gain an automatic 1.9% return on your investment.

Q: What is the best combi boiler for a 3 bed house?

A: The Rinnai M060SN is the best combi boiler for a 3 bed house. A 3-bed home requires 10.2 liters of hot water per minute and its heat requirements are in the range of 30 to 35kW. The Rinnai M060SN, with its 2.7GPM hot water output and more than 40kW heat output, can easily match these requirements.

Q: What is the best combi boiler for a large house?

A: The Noritz CB199-DV-NG is the best combi boiler for a large house with multiple bedrooms and lots of bathrooms. Such homes have large hot water and heating requirements and want a boiler that could provide more than 9 gallons of hot water per minute, which CB199 is capable of.

Q: What is the best combi boiler for 10 radiators

A: The Worcester 25i is the best combi boiler for 10 radiators. That’s because you need a 24-27KW radiator if your home has up to 10 radiators, 1-2 bedrooms and 1 bathroom. The Worcester 25i further sweetens the deal with its Energy Star certification and various innovative features, which we explained above.

Conclusion

Do you need a combi boiler? The fact that you’ve come this far tells us that you do.

We hope the information we provided has helped you to select the best combi boiler for your needs. We suggest preparing a checklist of factors mentioned in the buying guide and try to get a model which ticks all (or most) of the boxes.