Warm Air Heating Systems and Combi Warm Air

Although Warm Air Heating Systems have arguably fallen out of fashion in new properties, they have been one of the most efficient kinds of heating on offer over the past 4 decades.

In fact, the efficiency of traditional warm air heating has only been matched by radiator based systems in the last decade - and here at Hot Water and Central Heating Ltd we can offer advice based on our years of experience in working with warm air central heating .

We offer two main solutions, the Gas Warm Air heater, and and the Warm Air Combi.

NB: Those on oil fired warm air should go straight to the Warm Air Combi section.

Gas Warm Air heaters

There are just two manufacturers now covering the domestic residential warm air market in the UK.

New homes are no longer being built with warm air systems, and when older equipped houses come up for renovation, many of the existing warm air systems are removed and replaced with radiators.

Also, as our existing housing stock is extended with new kitchens and additional rooms, a warm air system is often found to be difficult to extend into these areas because the ductwork was often buried deep under the concrete floor.

A bit of history

In consequence, the market in the UK dwindles each year.  There used to be a large choice of suppliers in the UK such as;  Sugg, McCleary, Balmforth, Thorn, Sutherland, Halstead, Brink, Lennox and Johnson & Starley.  Out of these, only Johnson & Starley are still operating in the UK.

Lennox, based in the USA, and probably the largest warm air manufacturer in the World, pulled out of the UK in 2016 because the numbers didn’t warrant their investment.

Most existing Warm Air Units in UK housing stock are ‘open flue’ systems, where the heater is an archaic gas fire with a fan perched on top, or underneath, and there is a flue, or chimney, running to the roof.  In 2017 these type of units, by then still manufactured by Johnson & Starley for older housing stock, were withdrawn from sale due to low efficiency not meeting current EU standards.

Two current manufacturers

The Johnson & Starley Warmcair range was launched in 2013 and is now their main product.  This is a room sealed modern design .  Being a modern design, it can’t re-use the old chimney flue, however in some cases this can be replaced with their concentric flexible flue system.

The MultiCalor Udara is  made in Belgium and sold across Europe, including the UK.  Udara works in a different way to Warmcair and is more efficient, but does not offer a hot water heating option.  Like Warmcair, existing chimney hardware is incompatible.

Your options

Presently, there are 4 main options for a household with a defunct or old warm air unit.

  1. Replace it with radiators
  2. Replace it with a MultiCalor Udara
  3. Replace it with a Johnson & Starley Warmcair
  4. Fit a hybrid system such as the Warm Air Combi (further details follow)

MultiCalor Udara

The MultiCalor Udara is the latest condensing high efficiency gas warm air unit from MultiCalor Industries.  We’ve been fitting their products for over 10yrs and have found them to be very quiet and reliable.

A colour LCD panel allows the owner to programme operating characteristics including fan profile speeds and outputs, and see how the unit is operating.  Compared to the competition, this unit is a generation ahead.

Udara onboard touchscreen

Unlike older models, the Udara can match outputs with demand, so every model has a power modulation ratio of at least 5:1.  In other words, a 20Kw output Udara can run at less than 4Kw output when the weather is milder, and anywhere in between.

A modern programmable thermostat is provided with the units.

MultiCalor Udara room thermostat

The present-day warm air heaters enjoy considerable technical superiority over their predecessors. The contemporary models come equipped with the electronically controlled fan speeds and temperature regulation, thereby replacing the traditional on/off nature of old variants. So, the boilers of today operate in a subtler manner. These improved features lead to greater comfort and economic benefits for the householders when they think of upgrading.

MultiCalor Udara cutaway (upflow version shown, downflow similar)

A simple removable filter cassette is incorporated, this can be hoovered to remove dirt.

Johnson & Starley Warmcair:

Johnson and Starley, based in a large manufacturing centre in Northampton, transformed their range of warm air heaters into a new high efficiency range in 2013.  Recently further improvements have been made and we are pleased to offer them to customers for warm air upgrades.

Johnson & Starley Warmcair

Warmcair is made specifically for the UK market, and therefore many models incorporate a hot water heating function, unlike any of the imported units.


J&S Warmcair requires a hot water storage cylinder to be located somewhere in the house, this can either be an older vented cylinder, or a more modern mains pressure unvented type.  Many older warm air systems coming up for replacement need a hot water solution, and J&S are the only one box replacement.

All Johnson & Starley warm air products now come with a 5 year manufacturer warranty.

We are your local warm air specialist for Surrey, Kent, Sussex and South London, call us for details on 01732 866282, or use our email enquiry form.

We only offer repairs and servicing to equipment installed by us,  so our installation customers get the best possible service.


NB: If you want to add radiators into parts of your warm air equipped house, or mains pressure water systems, or have an oil fired or electric warm air system, take a look at our warm air combi solution on this page.

The Warm Air Combi:

Many of our customers have an antiquated old warm air unit and would now like to enjoy the advantages of a combination boiler in 2019, such as;

  • instant hot water
  • mains cold and hot water pressure to all outlets
  • economic hot water water production
  • no hot water cylinder needed

But don’t want radiators to disfigure their home………

For these, we offer the Warm Air Combi.  It comprises just two boxes, a simple warm air unit and a wall mounted combination boiler.

Simple, safe, convenient and economical.  It looks like this;

A gas or oil boiler, such as a Worcester Bosch wall hung unit;

2019 Worcester Bosch Style 8000

And one of our air handling units;

MultiCalor air handling unit

So, what is a MultiCalor Air Handling Unit?

Energy is supplied to it by an electrical supply for the varispeed fan and electronics, and a pair of pipes from the boiler containing heated water.  In simplified terms, it is a very large copper radiator with a varispeed fan.

Your old gas, LPG or oil fired warm air unit is removed and replaced with this neat box, which is coupled to your existing ductwork.  There’s no flue/chimney system, because the new unit uses energy from a boiler located somewhere else.  No gas ventilation required, no fire risk, no carbon monoxide risk from the unit.  Furthermore, the separate boiler can be one of your choice and it could provide your hot water, and run those radiators in the conservatory or the underfloor heating in your kitchen extension……

Here’s an example of one our jobs in 2018 below, (NB: there’s lot’s more examples in our Case Study section called Simon’s Blog);

New MultiCalor MC20 in Horsham, Sussex – ductwork altered to fit.

In this case it replaced a very old filthy oil fired unit;

Try selling the house with one of these in it

In this particular example, we provided a new hot water cylinder and a new Worcester Bosch oil  boiler in the garage, and left our customer with a modern, quiet, efficient warm air system, and internet control too….

New Worcester Bosch Oil fired Danesmoor in the garage

Warm Air Combi options;

  • 14, 20, 30 and 40Kw warm air capability
  • Can be linked to almost any type of Oil, Gas and LPG boiler(s)
  • Can add an unvented (Megaflo) hot water system for larger applications
  • Can be partnered with radiators in the same house
  • We can also offer Evohome and multi zone systems

Ask us for details.

You can find examples of our Warm Air Combi installations here;

Multicalor Warm Air

Afos warm air:

There are still some AFOS oil warm air units in the UK, these comprise an oil boiler coupled to an air handling unit.  We can offer replacements using Worcester-Bosch boilers and an air handling unit, for a modern, high efficiency home, using existing ductwork.  Email us for details, we work in a 30 mile radius of our base in Kent.

Customer Testimonials

Excellent Work

Excellent work , the workers were very efficient, considerate and tidy. They worked with the least disruption possible for an elderly lady. Any unexpected problem was dealt with safely and professionally. The finished heating is to a high standard. K.T. Kent

Jennie 05/05/2017