Furnace Undersized for AC???


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Old 07-10-11, 05:58 PM
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Exclamation Furnace Undersized for AC???

I had my AC replaced last year at the end of summer, but I held off on replacing my furnace.

This summer has been absolutely dreadful for my family, our AC can't keep up with the temperatures... I have had two seperate HVAC companies send technicians and both indicate the issue is that my furnace is undersized for my AC. My confusion is that my old air conditioner was capable of cooling my house and it was 25 years old. My furance is definitelly small but it has no problem heating my home.

I don't have the money to replace my furnace and it seems rediculous that I would get a new AC, only to have it be considerably worse and to have it be LESS effiicient to run. (Because it runs ALL day long)

Since I can't afford the replace the furnace.

Can I purchase Duct Fans: Will they fix the problem? Or is it something to do with how hard the air is blown onto coils or something?

Any ideas or are both companies correct and I have to replace my furnace because my new AC requires something stronger where my old AC did not...
 
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Old 07-10-11, 06:14 PM
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This sounds very odd to me. If they replaced with the same size unit it should be better than your old unit. Is your blower clean that will help get more air. ALS duct fans will do nothing. You can't push air that is not there to begin with. Was a heat load done to size the AC?
 
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Old 07-10-11, 06:21 PM
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I forgot to note - they replaced the blower on my furnace. They hoped that would correct the issue. But it barely made a dent into the problem. I'm unsure if they tested with that but they say the temperatures and all 'readings are good.' I have paid two other companies to look at it and they each say it's the furnace...

So inline duct fans right over the AC\furnace wouldn't help? Too bad... (Seemed too simple lol)
 
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Old 07-13-11, 07:25 AM
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air conditioning requires a higher volume of air. Not all blowers are rated for air conditioning. Most furnaces today are rated for the cfm that they will put out and form there can be matched to the size of a/c. a/c needs 400 cfm per ton. example = 3 ton a/c needs 1200 cfm
 
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Old 07-13-11, 07:04 PM
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My main agitation is that my new AC runs 24\7 and can't keep the house cold. My old AC which was like 25 years old and said to be a Seer 4 vs my seer 14 and my electic bill is like $80 more per month all summer long.

I had the old blower before (Same type as new one they put in) - why would an older\less efficient Ac COOL better and for less electric. We use our TVs less, have more ceiling fans and use energy efficient bulbs and bulbs... Our PCs are powered off most of the time.

Compared to last year, our TV was on nothing energy saving ect.... Now the only major difference is that the AC runs 247...

Is there anything I can do!! I can't afford an AC.
 
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Old 07-13-11, 07:33 PM
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Age of a unit has little to do with how well it cools. Was a heat load done on the home by the contractor.
 
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Old 07-13-11, 08:18 PM
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I'm not an HVAC pro, but your logic seems good to me. Old system was cooling sufficiently, new system should do the same for less money.

Do you know what size your old system was and what size this new one is?

What size is your home?

As Airman asked, did anyone do a heat load calculation to determine the correct size?

Was any other work done, like adding supply or return ducts? Or any other construction since the new ac was installed.

Does the air coming out of the supply registers seem cold? Can you measure it and the room temperature?

In addition to resolving the problem you have stated, you can also reduce your heating and ac requirements, but that should be looked at after this issue is resolved.

More information and the pros will respond.

Bud
 
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Old 07-14-11, 07:18 PM
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you have a sizing issue. the only time that thing should be running non-stop is on a 95 degree day. make sure that your indoor filter is clean, things as simple as this slip through the cracks sometimes. quick tests you can perform with a simple thermometer are indoor coil temp (should be about 40 degrees colder than your return ambient air temp) supply temp (should be about 20 degrees cooler than your return air temp). condenser discharge air temp (should be about 30 degrees hotter than you outdoor temp, this air comes from the top of the fan). with those 3 readings your wont get the best knowledge of how its running but it should tell you enough.
 
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Old 07-18-11, 12:01 PM
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Possible ?

Couple questions for you ? First is the air blowing out of the vents the same as it was before they replaced the fan Velocity wise ? It is possible they have wired the fan either too fast or too slow to cool the house . Too fast wont remove the humidity, to slow the home takes forever to cool . Id start with that first if the AC is the same ton as the old one
 
 

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