Heat Pump size; 4 ton, 3.5 ton, or 3 Ton

last year

I received 3 bids on a new heatpump. One quote is for a 4 Ton 17 Seer, another for a 3.5 Ton 17seer, and the final one is for a 3 Ton 20 seer.

My home is 2200 square feet, single level ranch with kitchen and living areas facing south, 15 registers, and 2 air returns. I would love a 20 seer but I'm questioning why I'm quoted for a 4 Ton and then another is a 3 Ton. It seems like that's a large difference?

My current set up is a 3.5 Ton 15 seer if that helps. But it's already failing and we've had it 13 years this May.

Featured Answer

Elmer J Fudd

last year

Different outcomes can result not only from slight differences in the inputs (many of which are estimates anyway) but also from what conclusion is drawn from the result. If the cooling load comes out to 3.6 tons, do you round down to 3.5 (one tenth of a ton difference is inconsequential) or do you round up (the old fashioned seat of the pants attitude, no one ever calls to complain they're too cool during hot weather). Arguably, half a ton isn't a huge difference either. One ton, different story.

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Comments (6)

sktn77a
last year
Has the 3.5 ton unit heated and cooled the house adequately in the past (excepting the most recent times when you think it's failing on you)? Single stage units come in 0.5 ton increments while multistage units only come in 1 ton increments.

(A 3 ton 20 SEER unit will be more efficient/kWhr of electricity but won't heat/cool as much as a 17 SEER 3.5 ton ot 4 ton unit).
ksd4423 thanked sktn77a
ksd4423
Original Author
last year
sktn77a, No, the 3.5 ton has not cooled or heated properly. Our south facing rooms are always warmer in the summer and during the winter it is always cooler by 4 degrees. We added fresh insulation in the attice and in the crawl space and also put in energy efficient windows and slider at the south end of the home. One of the companies went underneath and took pictures of the ductwork showing me leaks which I have always suspected. We are going to have those sealed.

My two top quotes are both for Daikin Fit. The first quote is for a 4T 17 seer. The 2nd quote was a 3.5T 17seer. Both are variable speed.

Charles Ross Homes: If they use an ACCA manual to calculate loads, why does one company think I need a 4 ton, and the other company a 3.5 ton?
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What they're probably telling you here is not that the new system is better but that your old system was oversized, and on the surface of it that seems like a possibility, since 3.5 tons is a lot for 1200 square feet in most cases. Someone is going to tell you to have them due a Manual J load calculation, and that's certainly good advice, but for the sake of discussion, how much does your current system run to keep the house cool on the hottest days? If your old system is running all day on the hottest days, you may have a house with high heat gain (possibly older construction, many windows, or high internal heat gain from living activities). But if your current system has run intermittently even on the hottest days, and I'm guessing that's the case, you probably have room to reduce the sizing, and this would give you better humidity control and reduce energy consumption.
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First of all, it is considered poor forum etiquette to start a new thread when you already have an active thread. Questions that you have not answered in earlier thread. What is the brand, model, size, and efficiency of existing propane furnace? What is its blower size rating? This is important if you are considering just adding on a heat pump with matching coil to existing furnace. If you really require a 5 ton, then this would most likely require significant ductwork modifications to handle the additional CFMs. Has any of the dealers mentioned this? Mighty important. What is your cost/gallon for propane? What is cost/KWR for electric? Tell us about existing problems with current system and location of problems? Basements at or partially below grade have low heating and cooling loads. Tell us about your average temp for both summer and winter? And extremes? What are your inside design thermostat setting for heating and cooling? How did existing 4 ton AC perform when it was working correctly as far as meeting your comfort requirements? The finished basement should have its own separate system preferred or at very least a zoning control. Any opportunity for insulation improvement/upgrade to basement area? I would want to see a separate load calculation for basement zone. Have you seen the load calcs in writing so that you can review? On the software letterhead? Post back. IMO
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"It shows needing 24,241 btu's cooling, with sensible load of 22,042 latent load of 2199, and and btu's of heating at 104,838" Your load calculation from loadcalc.net says you only need a 2 ton AC, but you need 110K BTU furnace for heating a 2200 sq. foot house in your climate. The numbers make no sense to me given that your climate is very similar to mine. The cooling load seems too low, and the heating load seems too high. You either entered the wrong values, or the free calculator is very poor at estimating. "None have provided a load calculation. I am guessing maybe a couple have done one." There is no need to guess. Either the contractor has done a calculation or he has not. Ask the question directly, and ask for a copy. Some contractors won't give you a copy because they don't want you to take their work and then buy form someone else. In that case ask him to show you a hard copy and have him explain it to you. If you were buying carpeting for the whole house, would you expect the contractor to come in and measure every room, draw up a plan on where the seams would be placed, and tell you options on how to minimize waste? What would you think if you got quotes from 5 carpet contractors each of which had very different amounts of carpet and none of them were what you estimated? Wouldn't you be asking "show me your measurements"? HVAC sizing is more critical than carpet sizing. If you buy too much carpet, you have left overs which you can either throw away, or put to some other use. The carpet that has been installed is not affected. If the HVAC is sized incorrectly, it will not function well, waste energy, on likely fail prematurely. All of that can be avoided by spending 30 minutes doing a correct load calculation.
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A couple of considerations. Heat gains and losses. It might be a good idea to have someone run a good Manual J heat load calculation just to make sure. If you're on the bubble, it might be a good idea to bite the bullet and add some ductwork. The newer and higher effiency equipment will NOT have the same heat capacities as the older equipment. The capacities will be given in the equipment manufacturer's catalog. Some of the newer equipment may not have the capacity of the "nominal" size. Make sure your contractor selects equipment based on the actual capacities based on the Manual J heat load and the equipment manufacturer's catalog ratings, not just nominal ratings. Sometimes there is a big difference. The main consideration when increasing the size if the equipment is making sure that you maintain .5 inches total external static pressure on the system. Occasionally this can be done by adding a damper. Sometimes though, it may require replacing the entire plenum and increasing the size of or adding ducts. The main thing to remember is that your system regardless of size is designed at .5 inches total external static to maintain proper airflow. I hope this helps. If you would like to do some further reading, please feel free to check out my blog HERE.
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Charles Ross Homes
last year
"If they use an ACCA manual to calculate loads, why does one company think I need a 4 ton, and the other company a 3.5 ton? " Good question. It may be that they haven't done any calculations and they're using a rule of thumb for sizing instead. If they have run the calcs, it could be that they are inputting different values for the area, insulation, glazing, etc. You'll need to ask them how they arrived at the size in their proposals.
mike_home
last year
last modified: last year
I am not familiar with the Daiken Fit whole house heat pump. I looked up the specification data for DZ17VSA 481A model. It shows a heating and cooling capabity of 45,500 BTUs. That's about 3.8 tons. the DZ17VSA 421A* model shows an output of 40,000 BTU or 3.33 tons. If the load calculation was about 3.5 tons, it is possible the installer decided to be conservative and move up to the next size.

You should ask for the heating and cooling load numbers, and what indoor and outdoor winter and summer design temperatures were used in the calculation. If you get no answer then I suspect no manual J calculation was performed.

Our south facing rooms are always warmer in the summer and during the winter it is always cooler by 4 degrees.

This likely is a supply duct problem and not a equipment size issue. You should ask each contractor how this will be addressed.
sktn77a
last year
"My two top quotes are both for Daikin Fit. The first quote is for a 4T 17 seer. The 2nd quote was a 3.5T 17seer. Both are variable speed."

Variable speed or inverter?

Heat Pump size; 4 ton, 3.5 ton, or 3 Ton

Elmer J Fudd

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Heat Pump size; 4 ton, 3.5 ton, or 3 Ton

Elmer J Fudd

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