I currently own a gas forced hot air 90 plus efficiency which is going on 20 years old. In November of 2014 I had the cicuit board replaced under a HVAC contract which covered all parts/labor. The unit has been running fine since then. I also have an outside AC unit (single stage)that is the same age and have replaced a capacitor once on it. I have noticed the last 2-3 years it has not removed the the humidity out of the house like it used to. I know that I want to replace the A/C unit this year. Where I’m hung up at is should I replace the furnace also to do it all at one time? By replacing them both I would consider a 2 stage A/C unit and acquire better humidity control. If I would only replace the AC unit to adapt to the current furnace, I would only be able to get a single stage AC unit. Are the 2stage AC units that much more efficient ? I live in Pennsylvania where I cool about 4.5 mtgs out of a year. Please provide me with your thoughts or guidance regarding this matter.
Thanks
Fredd
Replies
Generally speaking, it's easy to replace the AC of a forced air heating setup without the need to diddle with the air handler very much. The worst of it is that the evaporator unit inside the air handler may need to be replaced, to match the characteristics of the new condenser unit, but this is not usually difficult.
I don't know much about 2-stage AC units, but if your 90% furnace has a variable-speed fan it may already be able to accommodate the 2-speed AC.
Thanks for your reply. The current unit has a single speed fan. What's your opinion on replacing the furnace also seeing that it is 20 yrs old but still runs fine?
Thanks
My mommies furnace in central IL is now 63 years old. Inspected 3 years ago, replaced the fan motor (rubber bushings deteriorated) and fan blet and nothing else, still runs fine. Yours should be good for a few more years. Of course back then the HE was made out of thick stainless steel and was non-condensing.
Get yourself a set of old gauges ($10 on ebay) and check the AC pressures when running, compare to the chart inside the cover panel and recharge if needed. You can use propane (R290) to top off unless the air handler is in a basement.
OK, let us now hear from the peanut gallery on how R290 will explode the house and kill the family, etc........ been used in Europe for decades as refrigerant.
If you had a 30-40 year-old open flame 70% unit it would be an easy call, both because the unit would be worn out and because it would be costing you a bunch of money. But your unit likely has another 10 years of useful life left.
So it becomes a question of how stingy you are vs how much you want to minimize the future risk of breakdown, plus the 2-speed AC issue. And this, of course, depends to a non-trivial degree on your financial situation.
Fix What's Broke
Why would the air conditioner not be reducing humidity as it did before? That's the question you need to answer.
I object to replacing things just because they're "old." Twenty years isn't long at all! Even by the newer standards, 90% is pretty good.
A 90% furnace, btw, is almost certain to have a variable speed fan.
The air conditioning, by contrast, probably is worth replacing... as long as you get a new one, one that isn't using a refrigerant that's being phased olut of service.
I disagree with the poster who said to just fill it with propane. Air conditioners are a system ... changing the type of refrigerant also requires changing some internal parts (like the expansion valve), and very likely the compressor as well.
Why would a unit no longer remove humidity? The most likely cause is a unit so over-size that it runs only in short spurts.. Perhaps a supplimental dehumidifier is what you really want.
A proper servicing of the air conditioner will measure the 'superheat' of the unit, to see if it's performing properly. Using those gauges is one way this can be done; that's how you tell if you have the right amount of coolant in the system. The guy will also clean off the coils and make sure there's good air flow over them.
The main reason why the AC might not be reducing humidity as much as before (after verifying the fan's working properly and the filter isn't clogged, etc) would be an increased surface temp at the evaporator coil. This is normally due to the inability of the compressor to develop as much pressure as before.
(Minor refrigerant loss actually tends to lower coil temp, possibly resulting in icing and a failure to cool, but not typically impacting the ability to dehumidify. However, it would make sense to have the unit serviced before trashing it, as there could be some odd problem somewhere causing the symptom.)
And when the compressor itself starts to fail there's usually not much one can do other than to replace the entire outdoor condenser/compressor unit.
Based on my (somewhat limited) experience, a standard quality residential compressor will last 25-30 years in the temperate US. At 20 years it's a little early for the compressor to be showing its age, but not impossible.