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scotzz 03-20-2013 07:07 AM

New A/C for Ranch - Separate Air Handler vs Evaporator Coil in Furnace
 
Have an 1800 sq ft ranch built in the early 60's which I purchased 2 years ago. Currently it has central air with the evaporator coil mounted in the furnace. The a/c worked ok for the first summer but became weak last summer resulting in extremely high electric bills and difficulty cooling the house. I had the unit serviced and was told that the compressor is weak and air off the coil is not the proper temperature. I have an option to just replace the outside compressor/condensor unit but it may not be matched to the furnace/coil. The unit is 15 years old so I am just going to replace the entire system with high SEER 2-stage compressor unit. I can keep the same configuration with a new coil in the furnace or, convert to a separate attic located air handler/evaporator coil. The attic air handler costs substantially more since ductwork needs to be run to the ceilings in all rooms. I know the attic mounted coil/air handler will do a better job of cooling since cool air is duffused from the ceiling down. However, I don't favor the expense, complexity and having this equipment in a hot attic. On the other hand, the furnace mounted coil is not optimum for cooling since it blows cold air in at the bottom of the rooms. However, the furnace mounted coil provides the benefit of naturally cooling the basementthrough exposed ductwork.........this is without actually opening a vent down there. This is important to me since I have a 1/2 finished walk-out basement with two fully exposed outside walls. I would lose the benefit of natural basement cooling if I went with an attic air handler although the contractor says he could run a duct down to that area. So, cost aside, I would like to hear pros and cons for both of these configurations.

Thanks

beenthere 03-20-2013 04:31 PM

Is the new furnace going to be 2 stage also?

scotzz 03-21-2013 07:12 AM

Quote:

Originally Posted by beenthere (Post 1141686)
Is the new furnace going to be 2 stage also?

The furnace will be variable speed, I don't believe single or 2 stage apply

JScotty 03-21-2013 03:47 PM

Quote:

Originally Posted by scotzz (Post 1142046)
The furnace will be variable speed, I don't believe single or 2 stage apply

From my understanding it's not so much a furnace as it is an air handler. If that's the case then single/multi stage doesn't apply as there isn't any heat to be staging. To your bigger question I would recommend not putting the unit in the attic. On top of the fact that working on it when it's hot outside (when it's most likely to break) is a nightmare. But if you have a drain line stop up you've got the potential to have a bunch of water end up on your ceiling. As opposed to the basement where it is usually much easier to clean up. Especially considering it's going to be quite a bit of extra expense to put it there, I'd leave it where it is.

beenthere 03-21-2013 04:24 PM

Quote:

Originally Posted by scotzz (Post 1142046)
The furnace will be variable speed, I don't believe single or 2 stage apply

All VS blower gas furnaces are either 2 stage, 3 stage, or modulating.

av-geek 03-25-2013 08:54 AM

Is the new system a heat pump, or a straight air conditioner? If it is a heat pump, I would NOT recommend ceiling mounted vents at all! I lived in a house where it was heated with a heat pump with the vents in the ceiling, and the house was always cold. The difference between the floor and the ceiling was almost 10-15 degrees. The system did great in the summertime at keeping the house comfortable, but bear in mind, the leaks will be in an attic space that could get well over 120 degrees in the summertime. This could reduce the efficiency of the air conditioning side.

If you are only getting a straight air conditioner one option is to have the two systems integrated where the unit installed in the basement only heats, and the new system in the attic only cools. That way, you will have optimum ductworks for comfort for whatever system is running. This will not be the cheapest option though.

In my honest opinion, the most cost effective solution is to replace your system in the exact same location as the old equipment. This may not yield the best comfort during the summertime. I would however weight how much you use heat versus how much you use AC when making your decision. (If this is a home in Florida, I would make decisions based on AC, but in Maine, it would be on heating)

scotzz 03-26-2013 01:06 PM

Quote:

Originally Posted by av-geek (Post 1145253)
Is the new system a heat pump, or a straight air conditioner? If it is a heat pump, I would NOT recommend ceiling mounted vents at all! I lived in a house where it was heated with a heat pump with the vents in the ceiling, and the house was always cold. The difference between the floor and the ceiling was almost 10-15 degrees. The system did great in the summertime at keeping the house comfortable, but bear in mind, the leaks will be in an attic space that could get well over 120 degrees in the summertime. This could reduce the efficiency of the air conditioning side.

If you are only getting a straight air conditioner one option is to have the two systems integrated where the unit installed in the basement only heats, and the new system in the attic only cools. That way, you will have optimum ductworks for comfort for whatever system is running. This will not be the cheapest option though.

In my honest opinion, the most cost effective solution is to replace your system in the exact same location as the old equipment. This may not yield the best comfort during the summertime. I would however weight how much you use heat versus how much you use AC when making your decision. (If this is a home in Florida, I would make decisions based on AC, but in Maine, it would be on heating)

The new system will not be a heat pump but integrated heat/air conditioner running through the lower wall mounted heating ducts/vents.

techpappy 03-26-2013 03:53 PM

You can overcome cooling circulation concerns by programming the air circulator to stay in the " low/med speed" continuous "on" position until there is a call for cooling then it automatically kicks into Hi speed for the cooling cycle ...this can be done via the thermostat and configuring the controls on the new furnace. The heating would remain as is unless you have problem cold spots which would also benefit from a similar set up. The continuous low speed fan operation provides better circulation and helps to even out the temperatures throughout. During heating, could feel a little drafty due to room air temps being circulated over windows but, this isn't noticeable during cooling


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