Boiler heat and window ACs to a mini split

Updated September 2026 · ATX Mini Split King, Austin and Central Texas

Some Austin and Central Texas homes heat with a hydronic boiler and cool with window air conditioners. This page explains the setup in plain language, its honest pros and cons, failure signs, what a ductless replacement involves, and when not to switch. ATX Mini Split King is an independent HVAC and electrical contractor in Austin and Central Texas. Work is done to code by a TDLR licensed contractor. Phone (512) 297-7493.

Flat pricing, everything included

Those are materials and labor together, wired to code by a TDLR licensed contractor. Anything non standard gets quoted first, before a single tool comes out of the truck: a very long line set, an electrical panel that needs work, a difficult mount, a roof or masonry penetration, disposal of the old equipment. You hear the number before we start, not after.

What this kind of system actually is

A hydronic boiler heats water and sends it through pipes to radiators or baseboard heaters. Rooms warm from the metal surfaces, not from blown air. There is no ductwork for heat. Window air conditioners handle cooling. Each window unit sits in a window or a sleeved wall opening, pulls indoor air across a cold coil, and dumps heat outside. People in older housing and converted spaces around Austin often ended up with this pair because adding ducts later is messy and expensive. The boiler lives in a closet or garage. A circulating pump moves the water. A simple thermostat or several zone valves control which rooms get heat. In a long hot summer the window units run almost every day. In a short mild winter the boiler may sit idle for weeks at a time.

The two halves do not talk to each other. Heat is hydronic. Cooling is a separate plug in or hardwired window box. You set the boiler thermostat for winter and you set each window unit for summer. There is no shared indoor air handler. Condensate from the window units drips outside or into a pan. The boiler has its own flue or vent if it is gas. Electricity for the boiler is usually a dedicated circuit plus the pump. Window units often share household outlets or have their own. In additions and converted spaces the boiler piping may have been extended in a hurry, with extra radiators in a sunroom or a garage apartment. That is the system in plain terms. It is two different machines doing two different jobs in the same house.

Honest reasons people still have this setup

Heat from radiators is quiet and even in a way many people like. There is no fan noise from the heating side. Dust is not blown around. If the boiler and piping are in good shape, rooms can feel comfortable on a cold Austin night without dry blowing air. Some owners inherited the system with the house and it still works, so they leave it. Window units are cheap to replace one at a time. You can cool only the rooms you occupy. In a converted garage apartment or a small addition that never had ducts, the combination was often the least disruptive way to get heat and cooling. The boiler can last a long time if water treatment is decent and it is not cycled hard. Mild winters mean fewer hours of operation, which can stretch the life of a well maintained boiler.

Another real plus is familiarity. A homeowner who has lived with radiators for decades knows how they feel. Window units are simple. If one dies in July you can buy another and slide it in. There is no big outdoor condenser for cooling, only the window boxes. For a rental or a house you may not keep long, putting money into a full changeover may not make sense. The hydronic side does not leak conditioned air into an attic the way leaky ducts can. In a tight older bungalow the radiator heat can be pleasant. People also keep the setup because a previous owner already paid for the boiler and the piping is already in the walls and floors. Removing it later is extra work. Those are honest reasons it is still around in Central Texas, even with long summers.

Honest cons and limits of this pairing

The cooling side is the obvious weak point in Austin. Window units are loud. They block a window. They leak hot outdoor air around the frame if the install is sloppy. They are inefficient compared with a modern ductless head, though we will not talk numbers. In a long summer they run for months. One unit per room means several noisy boxes and several places for rain to get in. Security is worse with an open window frame. They do not dehumidify as evenly as a properly sized indoor head. Heat from the boiler is slow to change. If a cold front drops through Central Texas overnight, radiators take time to warm the mass of water and metal. Zoning can be clumsy if there is only one thermostat. Old piping can hide leaks in walls or under floors.

The boiler itself has limits in this climate. It is sized for heat, which is the smaller load here. It sits unused most of the year, then is asked to fire on the few cold weeks. Standing pilots, old controls, and mineral scale from hard water are common issues. A leak in a radiator or a pipe can damage floors and walls. Gas boilers need venting that must stay clear. You still have two systems to maintain, two places things can fail, and two energy bills that do not share equipment. Window units also wear the electrical outlets and can trip breakers on old wiring common in older Austin housing. In an addition the piping run may be long and poorly insulated, so heat is lost before it reaches the far room. Those are the real drawbacks.

Maintenance is split and easy to neglect. The boiler wants annual attention that many owners skip because it is used so little. Window units want cleaning and a cover in the off season that they rarely get. When both are old, you are one failed pump or one seized window compressor away from no heat or no cooling. Finding parts for an old boiler can take time. A cracked heat exchanger or a leaking section is a serious repair. In converted spaces the original install may never have been quite right, with undersized radiators or window units fighting west sun all afternoon. Living with the cons is a choice some people make on purpose. Others just have not looked at the alternative yet.

Signs this system is failing or near the end

On the boiler side, look for water on the floor around the unit, rusty pipes, kettling or banging when it fires, a pilot that will not stay lit, or a pressure gauge that will not hold. Radiators that stay cold at one end, or rooms that never catch up on a cold morning, point to sludge, air, or a dying pump. A smell of gas or soot around a gas boiler is a stop and call someone situation. Frequent cycling, or the boiler running long after the thermostat is satisfied, means controls or the heat exchanger may be tired. In Central Texas the boiler may only reveal these problems in December or January, which is a bad time to be without heat.

Window units tell you they are done in more obvious ways. They rattle, they ice up, they blow warm air when set to cool, they trip the breaker, or they leak indoors. The sleeves rot. The window frame is damaged. You are replacing a unit every couple of summers. In a hot Austin summer a failing window unit means one room is miserable while you wait. Combined with an aging boiler, you have a house that is uncomfortable in both seasons. Electrical panels in older homes may already be at the edge with several window units plus the boiler. Burn marks at outlets, flickering lights when a unit starts, or warm plugs are signs the electrical side is also tired. If repair quotes keep coming and parts are scarce, the system is near the end of its useful life in that house.

What a mini split replacement actually involves

ATX Mini Split King removes the window air conditioners and, if you choose, the boiler and as much of the hydronic piping as makes sense. Radiators can stay if you want them as objects, or they can come out. Window openings and wall sleeves are patched and made weather tight. Sometimes a small piece of siding or drywall is needed. The outdoor condenser sits on a pad or wall bracket, usually on the side or back of the house where it is allowed by code and neighbors. Line sets, the copper pair that carries refrigerant, run from each indoor head through a small wall penetration to the outdoor unit. Condensate from the indoor heads is piped to the outside or to a drain, with a pump if the run is uphill. That is the physical swap in outline.

Electrical work is part of the job because ATX Mini Split King is also an electrical contractor. A new dedicated circuit, disconnect, and whip to the outdoor unit are typical. Indoor heads need power as well, often from the same outdoor connection through the line set cover or a separate run. Old boiler circuits and window unit outlets can be made safe and covered. If the panel is full or the service is too small, that is a panel upgrade and it is quoted before work starts, not a surprise. Awkward mounting, a long line set across a long addition, or extra indoor heads beyond a simple layout are also quoted before work starts. For a straightforward one indoor head job the price is $1,500, materials and labor included. Two indoor heads are $2,500. Three are $3,500.

What the crew does in a day depends on how many heads and how much demo. A simple one or two head swap, with window units out and openings patched, often finishes in a single day. The boiler disconnect and some pipe capping can be the same day or a return if the piping is extensive. The customer decides where each indoor head goes, which rooms matter most in a long summer, and whether radiators stay or go. You decide if the old boiler flue chase gets used or closed. You decide on a wall, floor, or ceiling cassette style head if the room allows it, knowing non standard mounts are quoted first. ATX Mini Split King works to code as a TDLR licensed contractor. You get a clear picture of the standard price and any extras before tools come out. That is the process, not a mystery.

When we will tell you to wait

Do not switch if the boiler is healthy, the radiators heat the rooms you live in, and you only need cooling a few months in a way the window units still handle. Repairing a pump, a zone valve, or one window unit can be the cheaper and less disruptive path. If you plan to sell the house in a year, a full changeover may not return what you spend in this market. If the house already has unused ductwork from a previous system, finishing a ducted repair or a small ducted unit might fit better than hanging heads. We will tell you a mini split is not the right call when you want the exact feel of radiator heat and you are not willing to give that up. It is also the wrong answer when indoor head locations would fight furniture, art, or a historic interior you care about.

Waiting a season is often the better call. If it is October and the boiler just needs a cleaning, get through winter with what you have. If it is April and the window units still cool, wait until you see another summer of bills and noise. Central Texas has a long cooling season, but you do not have to decide in the first heat wave. If your electrical service cannot support a new outdoor unit without a heavy upgrade, and you are not ready for that cost, staying with window units on existing circuits may be wiser for now. If the house is in the middle of a remodel, coordinate so heads and line sets go in with the walls open, rather than cutting finished surfaces twice. ATX Mini Split King will tell you when a repair or a wait makes more sense.

Questions people actually ask

Can I keep my radiators if I install a mini split?

Yes. The hydronic piping can be capped and the radiators can stay in place as furniture or be removed. The mini split does the heating and cooling. Some people like the look of old radiators and leave them. Others want the floor space. That is your call. ATX Mini Split King can cap the system safely. If the boiler is removed, the gas or electric supply is made safe to code. Work is done by a TDLR licensed contractor. Call (512) 297-7493 if you want to walk a house and see options.

How long does install take in a boiler and window unit house?

A straightforward one or two head job with window units removed and openings patched is often one day. Taking out a boiler and capping pipes can add hours or a second visit if the piping snakes through several rooms. Electrical from an existing panel is usually same day. A panel upgrade is extra time and is quoted first. You should plan on the crew being in the house, with some noise and indoor dust from patching. Furniture in front of planned head locations needs to be moved. ATX Mini Split King will set expectations before the day starts. Phone is (512) 297-7493.

What if the line set must run a long way for an addition?

Long line sets, extra indoor heads, and awkward mounting are not in the flat figures. They are quoted before work starts. An addition or converted space at the far end of the house may need extra copper, extra cover, and extra labor. That does not mean it cannot be done. It means you see the number first. The $1,500, $2,500, and $3,500 prices are for standard runs and normal wall mounts, materials and labor included. ATX Mini Split King will measure the path and tell you if it is standard or not. Call (512) 297-7493 to have someone look.

Will a mini split heat well enough in a Central Texas winter?

For the short mild winters here, a ductless mini split is commonly used for heat as well as cooling. It will not feel like a radiator. Air moves. Some people miss the silent radiant warmth. If that feeling matters more than convenience, keep the boiler. If you want one system that cools through the long summer and takes the chill off in winter, the mini split does that job. Very rare hard freezes are when any heat pump works harder. Backup from a remaining radiator loop is possible if you leave the boiler, but that is two systems again. Be honest with yourself about the feel you want.

Who does the work and how do I start?

ATX Mini Split King is an independent HVAC and electrical contractor in Austin and Central Texas. Work is done to code by a TDLR licensed contractor. Call (512) 297-7493. Someone can look at your boiler, your window units, your panel, and your rooms. You will hear whether a standard one, two, or three head job fits, at $1,500, $2,500, or $3,500 with materials and labor included, or whether long lines, a panel upgrade, or awkward mounting need a separate quote before anything is scheduled. There is no pressure to change if a repair or a wait is the better path for your house.

Keep reading

Every replacement guide we have written is listed on the replacement guide hub. Next door to this page: replacing a floor console indoor unit with a ductless mini split, replacing a ceiling cassette indoor unit with a ductless mini split. Pricing, service area and the quote form all live on the ATX Mini Split King home page, and the Austin mini split cost guide covers what the rest of the market charges.