[skibum87]

I recently had two-2 ton ac units installed (one on a 3 ton furnace in basement, and another on 2 ton furnace in attic). My home is about 1900sq feet in New England. During 90-95 degree weather my two units seem to run for five minutes, and then shut off for five minutes. Is this system too large? Thermostat set to 70 downstairs, 72 upstairs. The tstat temp is being met around 5 mins (swing set around 1.25 degrees). It then kicks back on after around 5 min. The thermostat does have the 5 min delay built in. I am worried they are cooling too quickly. I called the company and the tech came out and determined attic furnace blower was at 1200CFM so he lowered it to 800 to match two ton ac outside. He also lowered the downstairs 3 ton blower from 1200 to 1000 to better match the two ton ac unit. He basically said to see how it goes the next time we get some heat....what are your thoughts on this?

 

[BaldLoonie]

Here in the steamy Ohio Valley, 1900 sq ft would be 2.5 ton for the average house. So if you, in a cooler climate with lower humidity, have 5 tons in 1900 sq ft, I'd guess you have about twice what you need. Probably could cool the whole house on the upstairs unit til it got really hot. Cool air falls. Give it a try!

 

[motoguy128]

IF you have a lot of shade, moderate window area nd good insulatoion, and not a lot of mass (not stone, brick or stucco exterior) that's abotu normal. Humidity isn't' that high right now, daily temrpature diversity is still pretty wide since the ground hasn't warmed yet so it's cool at night and the house doesn't get heat soaked like it does in July.

In my 3200sqft home in Iowa, I have 2 2-ton system as well and on a rescent 90F, humid sunny day, the upstairs (that gets heated by the roof) only run on 1st stage for about 50% of the time at most to maintain temp and downstairs maybe 25% of hte time on 1st stage since it's most impacted by solar gain through windows and occupancy and appliances. At 93-95F the upstairs run about about 100% of the time on 1st stage, and it's running flat out at about 102F in 2nd stage. I'm not sure about downstairs since it's a new system and I haven't seen it run through a summer yet.

I agree, 2 tons could probably cool the whole house. Reducing the airflow should help.

I don't think your groosly oversized. Zoning can be a challenge in some home nowadays if you want 2 systems with conventional equipment, since hte smallest size is 1.5 tons. I'm starting to think that there may be a solid market for 1 ton split systems and 30k BTU furnaces for upstairs zones if we can get contractors to not oversize equipment.

 

[George2]

I recently had two-2 ton ac units installed (one on a 3 ton furnace in basement, and another on 2 ton furnace in attic). My home is about 1900sq feet in New England. During 90-95 degree weather my two units seem to run for five minutes, and then shut off for five minutes. Is this system too large? Thermostat set to 70 downstairs, 72 upstairs. The tstat temp is being met around 5 mins (swing set around 1.25 degrees). It then kicks back on after around 5 min. The thermostat does have the 5 min delay built in. I am worried they are cooling too quickly. I called the company and the tech came out and determined attic furnace blower was at 1200CFM so he lowered it to 800 to match two ton ac outside. He also lowered the downstairs 3 ton blower from 1200 to 1000 to better match the two ton ac unit. He basically said to see how it goes the next time we get some heat....what are your thoughts on this?

Is your home a ranch or 2 story? From your description, it sounds like the furnace/air conditioning in the basement takes care of that area and then the attic system takes care of the main floor? Asking if the systems are to big (now) is like "water under the bridge". I agree with the others.......2-2.5 ton was all the home needs. I would run only the second floor (or attic unit) and I bet it'll be great.

What is the square footage of each floor?

 

[skibum87]

2 story-940ish sq. feet per floor. Correct, attic runs second floor basement runs the first floor.

 

[beenthere]

Probably should have been 1.5 tons each. And you still would have probably been slightly over sized.

 

[udarrell]

I recently had two-2 ton ac units installed (one on a 3 ton furnace in basement, and another on 2 ton furnace in attic). My home is about 1900sq feet in New England.
(Well, that's about 950-sf per floor; in your climate a 1.5 ton upstairs & a mere 1-Ton downstairs should handle it. Needed load calcs performed...!)

During 90-95 degree weather my two units seem to run for five minutes, and then shut off for five minutes.
(I'd say something else could be affecting the air-temp near the thermostat; cycling back on in only 5 minutes after a 1.25F temp-differential does not seem right. It might even cycle on sooner if it weren't for the 5 minute delay.)

Is this system too large? (Looks like it from here.)

Thermostat set to 70 downstairs, 72 upstairs. The tstat temp is being met around 5 mins (swing set around 1.25 degrees). It then kicks back on after around 5 min. The thermostat does have the 5 min delay built in. I am worried they are cooling too quickly. I called the company and the tech came out and determined attic furnace blower was at 1200CFM so he lowered it to 800 to match two ton ac outside. He also lowered the downstairs 3 ton blower from 1200 to 1000 to better match the two ton ac unit. He basically said to see how it goes the next time we get some heat....what are your thoughts on this?

Reducing the airflow ought to help some; however, I'd be trying to figure out why it is short-cycling on both thermostats; cycling off in 5 minutes & on again in 5 minutes is far too much cycling per hour.

You evidently have Temp-Swing adjustable thermostats; I'd also go to a higher temp-spread-swing until it provides the length of cycles you are trying to achieve. Then perhaps with another room thermometer see what the actual temp-swing is.

Those thermostat settings of 70 & 72F are awfully low; with adequate runtimes the humidity should be lowered enough to set those thermostats at around 76F, & with a little air circulation feel very comfortable...

 

[rock&roll4]

I go big

I also go big it may be wrong but when ever we did it right costumer would complain not cool enough they want 69 on any day they want to come home on a 90 to 100 degree day house 85 inside and cool down to 69 in a few hours. 76 would not cut it at any humidity for my costumers. I put ten minute time delay on condenser helps with short cycle.

 

[udarrell]

Whenever units are oversized the runtime is too short to bring down the humidity enough therefore, they won't feel comfortable unless it is close to 70F.

I have half-ton window units, one upstairs & one downstairs; in the hottest & humid weather they keep me perfectly comfortable.

It is important to dress for comfort & have good air circulation by using low energy use fans...

Some of the problem is psychological; they have gotten used to the 70F thing & think it's too hot if it's not 70 or below.

Some of the problem is that the Home & the system is not optimized for efficiency...every factor is important to human comfort...

 

[toocoolforschool]

The thing people (my wife) don't understand is the temp on the t-stat doesent reflect the humidity in the space so people see 75 and say oh it's to warm. To the op the t-stats might be in a bad location causing short cycling also.

 

[SBKold]

Do you have new honeywell thermostats per chance?