HVAC System Replacement

Can I Replace Just Part of My HVAC System?

The question of whether you can replace just part of your HVAC system, on the surface is pretty simple. An HVAC system is called a “system” because by definition a system is made up of components. The real question is should you replace just part of your HVAC system?

Depending on the type of system, there may be more or fewer components. Below are the major types of systems with a listing of the components. Of course the thermostat and ductwork are also technically considered part of the system. 

System TypeComponentsPartial Replacement Possible?
Split System Heat PumpCondensing Unit

Fan-Coil

Yes, Technically. Not advisable. 
Split A/C and FurnaceCondensing Unit

Furnace and Air-Handler

Evaporator Coil

Yes
Packaged A/C and Furnace

Packaged Heat Pump

All components contained in one caseNo. Repair or Full Replacement Only

 

In most cases the recommendation would be to replace the whole system at one time — there are a few reasons

  1. Cost — While it’s cheaper at the time to just replace part of the system, if you have to make repairs on the part you didn’t replace or end up replacing the 2nd part at a later date it will end up costing more than it would have to replace the entire system. A general rule of thumb would be about 40% more. 
  2. Reliability — The best way to ensure that you have a reliable system that only requires routine maintenance is to replace the whole thing. 
  3. Matching Performance — New systems are matched by 

There are a few cases where it makes sense however.

Some homeowners may inherit a system that has already had a partial replacement. In this case there may be a significant difference in ages between the major components. For instance the A/C condensing unit and evaporator coil may be 3-4 years old while the furnace might be 18-20 years old. In this case, you can assume there is lots of usable life left in the A/C and it would be advisable to consider just replacing the furnace.

Certain systems may experience a major failure in the A/C side of the system well before the furnace hits an age where it should be replaced. In general, the A/C usually fails before the furnace. The furnace is comparatively a simpler system with less points of major failure. The A/C components should provide reliable operation for at least 10 years. It’s possible the furnace could easily provide 15 or more years of reliable operation with proper maintenance. If you feel comfortable with the furnace and don’t mind the possibility that you may have a few repairs, you might be able to save a few dollars on your replacement by keeping the furnace. 

Summary and Recommendations

Making a good decision about going to a partial replacement can be difficult unless the circumstances are really obvious. Realistically you will probably need to rely on a recommendation from a professional as you weigh your options. Just keep in mind that it’s usually a little more trouble for a little less profit to do a partial replacement, so make sure you are getting good advice from someone that you trust and as always get a couple different opinions.