Gas vs. Hydronic Unit Heater: Pros and Cons

Unit heaters are stand-alone, compact heating systems that do not require any ductwork. They are typically larger than standard space heaters and therefore more durable and reliable.

Because they do not connect to an existing heating system, unit heaters are ideal for individual, decentralized heating. Large industrial buildings that have cold spots will often install wall unit heaters to not disrupt their existing ductwork. Spaces like garages, workshops, and building entrances also use unit heaters to manage air temperatures.

Unit heaters work by channeling a generative heating method like combustion or convection from burning gas or boiling water. Then, a heat exchanger transfers the thermal energy created by the fuel source. Types of heat exchangers include metal plates, finned coils, and tube bundles. Then, each unit uses a type of blower fan to move and circulate the air throughout an area.

Unit heaters can have different fuel sources, but the most common ones fall into two categories: gas and hydronic. Gas unit heaters use natural gas or propane as their fuel, combusting it in a furnace to create heat. Hydronic unit heaters, on the other hand, use hot water or steam from a boiler or heat pump. Radiation heats the air and distributes it throughout the room.

General unit heating benefits include lower installation and maintenance costs. Their singular compactness makes all their parts accessible and easy to repair and replace. For smaller spaces, their overall operating costs are also less than a ducted system would be. Beyond that, each type has its own benefits and disadvantages that make them suitable for different uses and environments.

Pros

Of all types of heating fuel sources, gas is the most widely used for home heating. Natural gas and propane are readily available and affordable fuel sources. Most homes have access to a natural gas line, and propane tank prices are generally inexpensive.

Gas-fired heaters also warm up faster than hydronic heaters because of the speed of gas combustion. If simplicity and speed are some of your priorities for your unit heating system, then a gas unit is a perfect option for you.

Cons

The downsides of gas unit heaters are mostly because they are forced air heating systems. If any dust or pollutants accumulate in the unit, then the blower fan will circulate it throughout the area. Luckily, most gas unit heaters have air filters that help catch any debris before the fan blows it out. Regularly cleaning these filters is important to maintain clean air quality and prevent harmful respiratory problems.

On top of that, you will likely need to have your gas unit heater regularly serviced to ensure there are no safety issues. Things like leaks, poor ventilation, and excess carbon monoxide buildup can all occur with gas heating. This can increase ongoing maintenance costs compared to other types of heaters.

Pros

Both hydronic and gas heating are energy efficient, but water is an overall better transferer of heat than air. If you’re looking for a high efficiency alternative to gas heat, then consider a hot water unit heater. Hydronic heating systems are roughly 30 percent more efficient than forced air systems.

Hydronic systems are also quiet, as they transfer heat through convection rather than blasting it with a forced air fan. Radiant heat systems, such as hydronic, are better at distributing warm air evenly throughout an area. If you’re worried about cold pockets or costly heat losses, a hydronic, radiant system can eliminate those concerns.

Cons

Compared to other types of systems, hydronic unit heaters are more expensive up front. The use of convection instead of gas combustion also means that they may not get as hot as gas unit heaters. For those in extreme climates, this could be a significant disadvantage.

Also, since there is no ventilation or air filtering, the air inside the water heater unit could get stale. Leaks are also a potential issue because of the many fluid pipes within the unit. Because hydronic heaters are more modern, maintenance costs are higher and replacement parts may be more difficult to find.

If you're still debating between the types, browse HomElectrical's selection of unit heaters to see more specifics up close. Once you’ve determined which unit heater is best for your needs, consult an HVAC professional for installation.