3.5 ton heat pump vs 4.0 ton heat pump
I've posted other threads today on my new split sytem heat pump. This thread is to ask about a 3.5 ton unit vs a 4.0 ton unit. Most of the quotes have been for a 3.5 ton unit. The latest Goodman quote was a 4.0 ton unit along with a 3.5 ton Carrier. He said for this SEER unit Goodman only had heat pumps available in even ton units.
What is the disadvantage of the 4.0 ton unit? Will the difference between a 4.0 ton unit and a 3.5 ton unit be noticeable in a humidity situation? Both systems are variable speed air handlers. Both qualify for the tax credit.
4.0-tons is bigger. Bigger = shorter run cycles. It takes about 10-minutes for the refrigerant in the system to stabilize when the unit first comes on. For those first 10-minutes, the indoor coil is getting gradually cooler and between about 8 and 10 minutes it finally reaches the dew point of the air flowing across the coil and can begin to dehumidify the house. If a 4.0-ton unit runs for a 12-minute cycle because it's bigger than needed, you will end up pushing the t-stat to a lower setting (longer run) to try and wring moisture out of the air. If 3.5 tons is what the house calls for by load calc, then that's the way to go. I'd also recommend installing a whole house dehumidifier for those days that are warm and wet but not steamy hot. If you prefer, you can install a 2-stage, 4.0-ton unit and that will operate at about 3.5-tons capacity on 1st stage and have some 'reserve' for extra hot days. Not the best way to go if the house really calls for 3.5-tons, IMO. I'd do the 1-stage w/WHD. Your money, your choice.
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Goodman's two-stage units are only available in full-ton increments. According to what I've read, stage one is roughly 75% capacity, or in your case - 3 tons. I have a DSZ - 18 , 4-ton unit installed in my house - it's quiet and works well. I believe it's oversized, (it replaced a 3.5 ton unit) , but my utility bills still went down substantially. I'd buy it again, especially when the price is compared to competing brands.
FWIW, Goodman also has a new "comfortnet" ready unit available with a communicating thermostat - it might be a worthwhile upgrade to consider.
You might also have a conversation with your contractor about where exactly your load calc is - if it's 3.2 tons, for example - you might be able to blow in some more insulation and get away with a 3 ton unit. I bumped my attic insulation to r-49 from r-19 and it made a nice difference in comfort for not alot of bucks.
I would go for the 3 ton even. You'll save money now, and during most outdoor conditions. And it will run at a lower fan speed, which should make it quieter.
If you find it really doesn't keep up on the very hottest days (which may add up to only a few hours per year), then you have an incentive to tighten your home: seal ducts and wall/ceiling penetrations. More attic insulation. Possibly windows.
Also, if it doesn't keep up and it is only a few hours, a box fan or a ceiling fan should keep you comfy.
whats the square footage of the house
what size did you have before
were there humidity issues before
did it cool during the hottest days
FWIW, one of the op's previous posts indicates 1550 sq/ft in the northeastern US. 3 tons might be excessive based on that info..
Unless the old unit is tested for the actual BTUH it is delivering to the rooms, you can't go by how it performed.
Many existing older systems don't deliver/REMOVE near their tonnage rating to/from (actually heat from) the rooms...
Last edited by udarrell; 08-30-2010 at 06:32 PM.
Reason: (actually heat from) the rooms...
My existing AC unit is a 3.5 ton carrier manufactered in 1998. Several of the quoters said it was a SEER 12 unit. It seemed to cool fine with no really noticeable humidity problems. The square footage of the house is around 1550 with a basement with 5 AC ducts and a return. I would say 2/3 of the basement is one large room with the ducts and return as mentioned. A door seperates this from the rest of the basement which contains my 40 year old gas hot water furnace and gas water heater. My home is located in the middle of the Shenandoah Valley (Waynesboro, VA).
I don't know what the Goodman model is. I will get that info before signing the contract. I know the air handler is variable speed but I don't know if it is a single or dual stage unit. The price is $4600 installed.
did the heat load call for. My own system is a Carrier Infinity 3 ton HP . Though the load was 2 1/2 ton , I went with the 3 ton because it is 2 stage . The system is almost always in in the first stage . the house has NO humidity problems ,very mush the opposite ,It cold in here @ 78°F
I'd look more at the heating load than the cooling load - your basement isn't going to require much if any cooling unless it's a walk-out or very exposed.
Originally Posted by shiflerg
For that area of the country, i'd insist on a two-stage - you'll have much longer run times which will help greatly with the humidity.
Make sure to familiarize yourself with the terminology as well - Goodman has both "variable-speed" and "multi-speed" air handlers - there is a difference...
SSZ16 - 3.5ton; DSZC16 - 3.5ton
Does the ssz16 come in a 3.5ton unit? Does the DSZC16 come in a 3.5 ton unit?
Thanks; I'm getting all kinds of good inputs.
neither is available in 1/2 ton increments. You'll find the price difference between the two is a nothingburger though. For my money, I'd get the dsz "c" model, which will work with the communicating thermostat if you want really good humidity control.
Originally Posted by shiflerg