Variable speed helps warm rooms?

8 years ago

Our 20 year old four ton ac unit is about to die (coil leak that’s not worth fixing). My ac guy offered the following:

1. Single speed $5900
2. Heat pump $6200
3. Variable speed $ 6700

We are in sw Florida so have the ac on for 6-7 months a year, and it goes down to the forties for a few weeks. So we are going with at least the heat pump.

Our house is 1950s with an addition in the 2000s. This unit will cool the original part of the house (probably 1500sf). Old windows and ductwork probably from the 1960s. The only part of ductwork I can see shows a round run wrapped in old brown paper. From a quick google search, it looks like this is metal wrapped in insulation. Currently, two bedrooms have bad air flow and stay several degrees warmer than the rest of the space. One is about twenty five feet from the unit with a few turns. The other is in the room right next door to the unit, but the ac guy thought it might have several turns in the ductwork.

The ac guy can replace ducts for $350 a piece (we would likely need to replace 5 or so), but felt that the variable unit could likely resolve the problem by itself.

First question: any benefit generally to spending $500 on a variable speed unit? Does it make a difference in Florida?

Second: will variable speed really help the flow problems in those rooms? Or is this a ductwork problem? Or is old ductwork dangerous stuff that we should just leave and suffer with a temp differential?

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Comments (5)

mike_home
8 years ago
You should spend the money and fix the duct work. Fixing it is not dangerous. I highly doubt there is any asbestos in the insulation.

The variable speed is will help lower humidity which is a good feature for Florida. Is is not a cure for poor duct work.

If you want feed back on the equipment and prices then post the model numbers of all equipment (condenser, air handler, and thermostat).
H202 thanked mike_home
H202
Original Author
8 years ago
The equipment is definitely needing replacement. The inside unit is 21 years old, and had the capacity to be a heat pump, but apparently the outside unit died and was replaced with a used unit that does not support heat pump, and it's totally rusted through. I'm fine replacing it. (As an aside, we are planning on re-doing our kitchen next year and would be moving the a/c unit then to help the floorplan -- so we'd replace it then anyway).

So as a general matter, 50 year old ductwork is a likely reason for bad airflow?
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sktn77a
8 years ago
last modified: 8 years ago
"So as a general matter, 50 year old ductwork is a likely reason for bad airflow?"

No, the addition that draws from a system that wasn't designed for it is the issue. Get the ductwork redesigned and replaced (use metal, insulated ducts, where possible, not flexduct). And don't forget the returns.
H202 thanked sktn77a
H202
Original Author
8 years ago
To clarify, the addition has it's own two a/c units. This unit only cools the original part of the house. So the addition didn't add on to this original ductwork.
PRO
Austin Air Companie
8 years ago
Due to location a variable speed blower can help with humidity to a certain degree when paired with a 2 speed condenser. Heat pumps also come in 2 speed varieties as well which in your climate would probably make this a better choice if you plan to stay at this property for at least 10-15 years.

If you match a single speed air conditioner to a variable speed blower it will provide you slightly better efficiency and it will run quieter provided the duct system you attach it to is adequate.

If this property is a lifetime home: (you have no desire to move) It may pay you dividends to look into Inverter AC system or Inverter Heat pump system whichever you are considering. Because of your location there is nothing better in terms of dehumidification control, better efficiency and typically better warranty coverage from manufacturer as well.

Reducing humidity in your home a mere 5% will make you much more comfortable even at a higher temperature.

I live in a humid climate as well: I service the Katy, Texas area.