If you refurbish homes for the rental market, heating is one of the few line items you cannot skimp on and cannot overspend on either. Tenants expect instant hot water and warm rooms, your Gas Safe engineer needs something they can fit and service quickly, and your spreadsheet needs a number that does not blow the refurb budget.
This guide is written for private landlords, HMO operators, housing associations and anyone renovating houses to let. It covers three proven all-gas setups, what each one costs in hardware, which products to buy, low-cost smart controls that help you spot damp and wasted heat, and how the installation fits together, so you can brief your installer with a clear specification instead of an open cheque.
The cheapest heating system is rarely the cheapest boiler. It is the one with the fewest parts to buy, fit, certify and repair over the life of the tenancy.
Pick your setup in four questions
Answer these before you buy anything. They point you straight to one of the three setups below.
How big is the property?
Up to about 10 radiators and one bathroom points to a combi. 15 or more radiators, or several bathrooms, points to a heat-only boiler.
What pipework is already there?
An existing combi is a like-for-like swap. An older open-vent system with tanks in the loft suits a heat-only boiler, which can also be converted to a sealed system.
How much hot water at once?
One shower at a time is fine on a 24kW combi. Two showers running together, or an HMO with a morning rush, needs 16 L/min from a multipoint.
Is there mains gas?
No mains gas? The E-Combi ONE ships with an LPG conversion kit, and there is a dedicated LPG multipoint for off-grid lets.
The three all-gas setups
The Workhorse Flat: combi boiler, compact radiators, wireless stat
Best for 1 to 3 bedroom flats and terraced houses with one bathroom. This is the lowest-cost way to deliver heating and on-demand hot water from a single appliance, with no cylinder, no tanks and no loft pipework.
- Boiler: Ariston E-Combi ONE 24kW (30kW if there are two bathrooms). It is sold boiler only, so add the Ariston HE horizontal flue kit (3318073, £59.95).
- Radiators: white K2 compact radiators sized to each room with our BTU calculator.
- Controls: Drayton Wiser Thermostat Kit 1 for app control, OpenTherm boiler control and room-by-room expansion. Choose the Multi-Zone Kit 1 if you want two radiator thermostats included from day one.
Hardware from about £1,340 for a 2-bed flat with five radiators, including the flue and smart controls. Valves and fittings are extra. See the worked budget below.
The Big House or HMO: heat-only boiler, underfloor heating, multipoint hot water
Best for larger houses, HMOs and conversions with high heat demand. The Baxi 625 heat-only boiler handles space heating (radiators, underfloor heating or both) while a gas multipoint water heater delivers hot water on demand. You get a large-house heating output without buying, housing or certifying an unvented hot water cylinder.
- Boiler: Baxi 625 Heat Only 25kW with a 7-year parts and labour warranty and a telescopic flue included.
- Sealed system: Heating Expansion Vessel Part L Filling Kit. Converting an old open-vent system to sealed removes the loft feed and expansion tank and the frozen-tank callouts that come with it.
- Heat emitters: water underfloor heating on the ground floor, compact radiators upstairs.
- Hot water: Biasi Multipoint 16S (horizontal flue included) or Ariston Next Evo X 16, both 16 L/min, enough for a shower and a basin at the same time.
- Controls: Drayton Lifestyle RFPT wireless programmable thermostat for time and temperature control of the heating circuit.
Core hardware from about £2,080 (boiler, 8L vessel kit, Biasi multipoint and thermostat), plus pump, underfloor manifold and radiators.
The Multipoint Add-on: extra hot water where the boiler cannot reach
A gas multipoint is also the landlord's fix for awkward layouts: a loft-conversion en-suite a long pipe run from the combi, a second kitchen in an HMO, or an annexe. It serves several taps from one wall-hung unit, fires only when a tap opens and needs just 0.2 bar of water pressure to start.
- Natural gas, lowest price: Biasi Multipoint 16S, 16 L/min.
- Natural gas, slimmest: Ariston Next Evo X 16, 187mm deep for cupboard installs.
- Off-grid LPG: Ariston Next Evo X 11 LPG, 11 L/min for one outlet at a time.
From £390 per unit, plus a fused spur. The Biasi includes its horizontal flue; the Ariston Next Evo X units need the SE flue kit 3319648 (£49).
Why gas still wins on a landlord's budget
- Lowest upfront cost per kW. A 24kW combi costs less than most 9kW electric boilers and delivers far more hot water.
- Cheaper to run for tenants. Per kWh, mains gas costs a fraction of the price of electricity under the UK price cap, which helps with lower bills, fewer complaints and longer tenancies.
- Every engineer knows it. Any Gas Safe engineer can service, repair and certify these appliances, so you are not waiting on a specialist.
- One annual check covers it all. Your yearly Gas Safety Record (CP12) visit can cover the boiler and multipoint in the same appointment.
- Proven parts. Baxi, Ariston, Biasi and Drayton parts are stocked by UK merchants, so a breakdown is a same-week fix, not a same-month one.
Side-by-side comparison
| Setup | Best for | Core hardware from | Hot water | Watch-outs |
|---|---|---|---|---|
| A: Combi + radiators | 1–3 bed, 1 bathroom, up to ~10 rads | ~£1,340 (2-bed) | 10.4 L/min (24kW) or 12.5 L/min (30kW) | One shower at a time; flue sold separately |
| B: Heat-only + UFH + multipoint | Large houses, HMOs, 15+ rads | ~£2,080 core | 16 L/min from multipoint | Two flues; needs external pump and controls |
| C: Multipoint add-on | Remote en-suites, annexes, second kitchens | £390–£519 per unit incl. flue | 11–16 L/min | Needs gas supply sized for 22–30kW |
| Bathroom UFH kit | Tiled bathrooms on any wet system | £307 | n/a | Floor build-up; connect near flow and return |
Worked budgets
2-bed flat, Setup A
| Item | Qty | Price each | Line total |
|---|---|---|---|
| Ariston E-Combi ONE 24kW (boiler only) | 1 | £635.00 | £635.00 |
| Ariston HE horizontal flue kit 3318073 | 1 | £59.95 | £59.95 |
| Drayton Wiser Thermostat Kit 1 (2nd Gen) | 1 | £170.00 | £170.00 |
| 600x1000mm K2 compact radiator (lounge, bedrooms) | 3 | £107.00 | £321.00 |
| 600x600mm K2 compact radiator (kitchen, hall) | 2 | £77.00 | £154.00 |
| Hardware subtotal | £1,339.95 |
4-bed HMO, Setup B (core plant)
| Item | Qty | Price each | Line total |
|---|---|---|---|
| Baxi 625 Heat Only 25kW | 1 | £1,530.00 | £1,530.00 |
| Expansion Vessel Part L Filling Kit (8L) | 1 | £57.00 | £57.00 |
| Biasi Multipoint 16S (horizontal flue included) | 1 | £430.00 | £430.00 |
| Drayton Lifestyle RFPT wireless thermostat | 1 | £63.00 | £63.00 |
| Core plant subtotal | £2,080.00 |
Prices include VAT and were checked in September 2026. Valves, pumps, fittings and labour are extra. Vessel size is chosen by your engineer based on system water content, so the 8L kit is a starting point, not a specification.
Boilers and flues
Ariston
E-Combi ONE 24kW / 30kW Combi Boiler
Stainless steel heat exchanger, 94% seasonal efficiency and a 1:7 modulation ratio that stops short-cycling in small, well-insulated flats. The LPG conversion kit and wall bracket are in the box. Boiler only, so order the flue separately.
£635.00 inc. VAT
Ariston
HE Horizontal Flue Kit 60/100mm (3318073)
The standard through-wall coaxial flue for the E-Combi ONE. The 1000mm kit covers most UK wall thicknesses, can be cut on site and pushes together with lip seals, so no clamps or sealant.
£59.95 inc. VAT
Baxi
Baxi 625 Heat Only Boiler 25kW
Built for larger homes with 15 or more radiators. Works on open-vent or sealed systems, needs no pump overrun or permanent live, and comes with a 7-year parts and labour warranty and a telescopic flue.
£1,530.00 inc. VAT
Zilmet (Trade-Tec)
Heating Expansion Vessel Part L Filling Kit
Vessel, safety valve with gauge, braided filling loop and wall bracket in one order. It is the kit that turns a heat-only boiler into a sealed system. Available in 8, 12, 18 and 24 litres.
From £57.00 inc. VAT
Smart controls: simple, affordable home automation
A basic programmable stat meets the minimum rules, but a smart system does far more for a landlord for not much more money. The Drayton Wiser 2nd Generation range runs from one hub: start with a thermostat kit, then add radiator thermostats and £25 sensors room by room, all in one free app with no subscription.
Early warning for damp and mould
A humidity sensor in the bathroom or a north-facing bedroom can alert you when humidity stays high, so you can check ventilation before mould appears. For social landlords working to Awaab's Law timescales, that early signal is valuable.
No heating the street
A window sensor tells the radiator thermostat in that room to back off while the window is open. The radiator heads also detect a sudden temperature drop on their own.
Room-by-room control in HMOs
Give each let room its own radiator thermostat and schedule. One hub handles up to 16 rooms and 63 Wiser devices, so an empty room is not heated while a tenant is at work.
Void periods and frost protection
Between tenancies, set Away mode from your phone, keep a low background temperature and use a door or motion sensor to know if someone enters the property.
Drayton Wiser
Wiser Thermostat Kit 1 (2nd Gen) for Combis
HubR plus wireless room thermostat. Controls the combi by OpenTherm or relay, runs from the Wiser Home app with Alexa and Google, and needs no subscription. Add radiator thermostats and sensors to the same hub later.
£170.00 inc. VAT
Drayton Wiser
Wiser Multi-Zone Kit 1 (2nd Gen) for Combis
Everything in Kit 1 plus two radiator thermostats, so bedrooms can run on their own schedules from day one. Heads fit over 95% of existing radiator valves and ease off automatically when a window is opened.
£315.00 inc. VAT
Drayton Wiser
Temperature and Humidity Sensor (CCT593012)
Reports room temperature and humidity to the app, with a 5-year battery. Use it as a discreet thermostat in rooms that do not need a display, or set a humidity alert for bathrooms and bedrooms.
£25.00 inc. VAT
Drayton Wiser
Window and Door Sensor (CCT591012)
Magnetic open/close sensor that sticks or screws to any frame. Set a rule to turn a room's heating down while its window is open, or get an alert if a door opens in an empty property.
£25.00 inc. VAT
Drayton Wiser
Motion Sensor (CCT595012)
Battery PIR sensor that also measures light level. Useful in void properties and communal hallways, where it can send an alert or switch on lighting through a Wiser smart plug.
£27.00 inc. VAT
Drayton (budget option)
Lifestyle RFPT Wireless Programmable Thermostat
A 7-day wireless stat with receiver, so no chasing walls between tenancies. Installer-set min and max limits stop tenants overheating the property or turning it down far enough to invite damp.
£63.00 inc. VAT
Starter automation pack for a 2-bed let
| Item | Qty | Price each | Line total |
|---|---|---|---|
| Drayton Wiser Thermostat Kit 1 (2nd Gen) | 1 | £170.00 | £170.00 |
| Temperature and humidity sensor (bathroom, main bedroom) | 2 | £25.00 | £50.00 |
| Window and door sensor (front door or main window) | 1 | £25.00 | £25.00 |
| Motion sensor (hallway) | 1 | £27.00 | £27.00 |
| Pack subtotal | £272.00 |
Respect your tenants' privacy. Use motion and door sensors in void properties and communal areas, not to watch occupied homes. Agree with tenants who has access to the app, and remember the hub needs a Wi-Fi connection. In single lets that is usually the tenant's broadband. The HubR must be hard-wired by a competent person.
Multipoint gas water heaters
A multipoint heats mains water as it flows, so there is no stored hot water to lose heat, no cylinder cupboard and no cylinder to replace. Pair one with a heat-only boiler (Setup B) or use it to serve a remote bathroom (Setup C).
Biasi
Multipoint 16S 30kW, 16 L/min
The best-value 16 L/min option. It holds the set temperature when a second tap opens, starts at 0.2 bar and has a child lock that caps the output at 48°C. ErP A with a 2-year guarantee (register within 30 days).
£430.00 inc. VAT
Ariston
Next Evo X 16 Natural Gas, 16 L/min
Only 187mm deep, so it fits kitchen and airing cupboards. It has an oxygen-free copper heat exchanger, an ECO mode and temperature stabilisation. Add the SE flue kit 3319648.
£470.00 inc. VAT
Ariston
Next Evo X 11 LPG, 11 L/min
For off-gas-grid lets, holiday lodges and rural cottages on bottled or bulk LPG. It supplies one outlet at a time and is only 165mm deep. Add the SE flue kit 3319648.
£390.00 inc. VAT
Ariston
SE Horizontal Flue Kit 60/100 (3319648)
The stainless steel through-wall flue for both Next Evo X models, 800mm long with elbow, clamp and seals included. It is not interchangeable with the HE flue used on Ariston boilers.
£49.00 inc. VAT
Radiators and the bathroom decision
Compact radiators are the cheapest heat emitters per watt you can buy, and standard sizes drop onto existing pipe centres without re-plumbing. Use K1 single panels for hallways and small bedrooms, and K2 double panels where you need more heat from the same wall space.
| Radiator or valve | Best for | Price |
|---|---|---|
| 600x600mm K1 single panel | Hallway, WC, box room | £43.00 |
| 600x800mm K1 single panel | Small bedroom | £57.00 |
| 600x1200mm K1 single panel | Wide window, narrow room or behind a door (1,017W) | £89.00 |
| 600x500mm K2 double panel | Kitchen, under a short window | £65.00 |
| 600x600mm K2 double panel | Kitchen, hall with an external wall | £77.00 |
| 600x1000mm K2 double panel | Double bedroom, lounge | £107.00 |
| 600x1200mm K2 double panel | Larger lounge | £120.00 |
| Evolve Contract 15mm TRV / Evolve angled TRV | Every bedroom and living room radiator | £7.30 / £9.30 |
Fit TRVs as standard. Part L expects room-by-room temperature control on new and replacement systems, TRVs are the cheapest way to provide it, and they leave the door open to Wiser radiator thermostats later. Check the valve body fits the smart head before you order a batch.
The case for a bathroom underfloor kit
A single-room water underfloor kit connects to the radiator pipes you already have, so the bathroom is heated by the same gas boiler as the rest of the house. That is why it is cheap to buy and cheap to run:
- No extra boiler zone or whole-house manifold. The kit includes its own Grundfos pump and controls and tees off the nearest flow and return.
- Gas running costs, not electric. An electric mat of the same size draws power at electricity prices. The water kit uses heat your boiler is already making.
- Warm tiles dry faster. A warm floor helps a bathroom dry out between showers, which means fewer damp and mould complaints, a big issue for housing associations and HMO operators.
- Frees the wall. No radiator to work around when fitting a vanity unit, bath or shower screen in a small rental bathroom.
Read our guide to connecting underfloor heating to radiator pipes for the full explanation.
The simpler alternative: a towel radiator
If the floor is not being lifted, a towel rail on the heating circuit is the lowest-cost option. It heats the room and dries towels in one unit, and a heated rail next to the shower helps with condensation too.
AIZO Quality Heating
Single Room Water Underfloor Heating Kit
Room kits with a Grundfos pump, thermostat and controls that run off an existing radiator circuit. Sized from bathroom-scale rooms up to large kitchens.
From £307.00 inc. VAT
Reina
Diva Chrome Curved Towel Rail 600 x 800mm
A straightforward, well-priced curved chrome rail with 1,363 BTU at Δ70°C, enough for a typical small rental bathroom. Suitable for central heating, dual fuel or electric-only use.
£120.00 inc. VAT
How the installation comes together
Here is the order of works for a typical refurb, and who does each job. Gas work must always be carried out by a Gas Safe registered engineer.
Survey and size the systemHeating engineer
Measure each room and run the numbers through our BTU calculator to size the radiators. Your engineer confirms boiler output, flue route and gas pipe size. A 30kW multipoint needs a gas supply that can carry the load alongside the boiler.
Clean the old systemHeating engineer
Flush existing pipework before a new boiler goes on. Sludge from old radiators is the most common cause of early boiler failure and can affect warranty claims. Add inhibitor at the end.
Lay underfloor pipe and fit radiatorsPlumber or competent builder
Underfloor pipe goes down during the floor strip-out, before screed or boards. Radiators hang on concealed brackets. This first-fix work can often be done before the heating engineer's main visit, which saves day rates. See our water underfloor heating install guide.
Fit the boiler and flueGas Safe
A combi replaces the old boiler in place. For a heat-only system, the engineer adds the circulating pump and controls. If converting from open-vent to sealed, they fit the expansion vessel kit and remove the loft feed and expansion tank.
Fit the multipointGas Safe and electrician
Wall-hung within flue distance of an external wall, with its 60/100mm coaxial flue (SE kit 3319648 for Ariston Next Evo X) and a fused spur. Hot water pipes run from the unit to each tap it serves.
Connect the bathroom underfloor kitHeating engineer
The kit tees into the nearest radiator flow and return and runs on its own pump and thermostat, so it works independently of the rest of the house.
Set the controlsInstaller
Connect the Wiser HubR to the boiler (OpenTherm where supported), pair the room thermostat, radiator heads and sensors, and set a sensible schedule and any humidity or window rules. On an RFPT, lock the min/max range (for example 18 to 22°C). Hand over app access in line with what you agreed with the tenant.
Commission and registerGas Safe
The engineer completes the Benchmark checklist, notifies Building Control through Gas Safe and issues your Gas Safety Record. Register every manufacturer warranty straight away. Biasi requires registration within 30 days of purchase.
Landlord compliance checklist
- Annual Gas Safety Record (CP12) covering every gas appliance, with a copy for tenants.
- Benchmark commissioning checklist completed and left with the boiler. Most warranties depend on it.
- Building Regulations notification of the new boiler, handled by your Gas Safe engineer.
- Boiler Plus (England): new gas boilers need time and temperature controls. Combis also need one extra energy-saving measure: load or weather compensation, flue gas heat recovery, or a smart thermostat with automation and optimisation. A smart system such as Drayton Wiser, connected by OpenTherm, is a common way to meet this; confirm the route with your engineer. See our Part L guide.
- EPC and minimum energy standards: an efficient condensing boiler with proper controls supports your EPC rating. Check the current minimum band for your property type before you let.
- Warranty registration for the boiler and multipoint, filed with the property records.
Landlord FAQs
Combi or heat-only: which is cheaper for a rental?
For flats and small houses with one bathroom, the combi is cheaper to buy and install because it replaces both the boiler and the hot water system. Heat-only makes sense in large houses and HMOs where the heating load is high, or where keeping existing open-vent pipework avoids a costly re-pipe.
Why use a multipoint instead of a hot water cylinder?
A multipoint gives unlimited hot water on demand from one compact wall unit. There is no cylinder to buy or house, no stored water losing heat all day, and no unvented cylinder with its own servicing requirements. The trade-off is flow rate: 16 L/min comfortably runs a shower and a basin together but not three showers at once.
Can underfloor heating really run off my radiator pipes?
Yes, with a single-room kit designed for it. The kit's own pump and controls take water from the radiator circuit and bring it to a safe floor temperature. It is ideal for bathrooms and kitchens in a refurb where the floor is already coming up.
Can tenants override the thermostat?
On the budget Drayton Lifestyle RFPT, the installer can set minimum and maximum temperature limits. Setting both to the same value turns it into a fixed-temperature stat. A narrow band such as 18 to 22°C gives tenants some control without the extremes that lead to big bills or damp.
Do smart controls cost anything to run?
There is no subscription for the Drayton Wiser app, scheduling or voice control. The sensors run on batteries (about five years for the humidity sensor), and the hub uses the property's Wi-Fi. Agree app access with your tenant, and keep motion and door sensors for void periods and communal areas.
I have properties without mains gas. Does this still work?
Yes. The Ariston E-Combi ONE ships with an LPG conversion kit that your Gas Safe engineer fits at commissioning, and the Ariston Next Evo X 11 is a dedicated LPG multipoint for off-grid cottages and holiday lets.
Do you supply landlords and housing associations in volume?
Yes. If you are specifying several properties or a full block, send us your room schedules and we will quote the full package, with free UK mainland express delivery on most orders.
Specifying more than one property?
Send us your room list and we will price the boiler, hot water, radiators and controls as one landlord package.
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