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Old 08-01-2012, 04:50 PM   #1
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Update Furnace or Condenser first?


So I have tons of questions but don't want to DIY this so I want to ask questions here before I ask my HVAC tech.

Should I upgrade my furnace before my AC condenser or vice versis? This is due to cost reasons.

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Old 08-01-2012, 05:01 PM   #2
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Update Furnace or Condenser first?


OK so, How old are these units and are they currently sized to match? What condition are they in? Is your priority heating/cooling where you are located. Everything being equal, first thing I would do is check out sizes, types and efficiencies of new units. A new high efficiency furnace, ( i shouldn't but, I will assume you are talking natural gas) may or may not have the right fan capacity to work well with existing AC..ask about all of these things and about any possible problems you may encounter by mixing and matching. It's a start!

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Old 08-01-2012, 07:16 PM   #3
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Update Furnace or Condenser first?


if your a/c works you will probably gain by changing furnace first...
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Old 08-01-2012, 10:33 PM   #4
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Update Furnace or Condenser first?


Depends on which is older. Keep in mind, swapping out the outside unit also means swapping out the A-coil. Newer indoor or outdoor unit can also change in size of tons. That means that if the current units are 2.5, and updates have been made to make the house more efficient (newer windows doors, more insulation & air sealing), it could bring it down to 2 tons.

So best bet is to look at what is the oldest unit, and then go from there. Usually people go for the whole package, because a lot of times you get a discount not only from your energy supplier, but also can possibly get from the manufacturer of the equipment.
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Old 08-02-2012, 08:30 AM   #5
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Update Furnace or Condenser first?


Ok I'll add some more to the story. The outside unit is 2.5tons and is nordyne, it's a 1992 Seer 8 model single speed. The furnace, natural gas, is a goodman 90k btu single speed 1990 80% one. It heats and cools my house fine, but is old and I would like to research/replace before I have to because then I'm paying the "I NEED NOW" rate.

Updates: I added attic insulation up to R49 (was R9 before), I added new triple pane low E argon filled windows (was wooden single pane before). Now I plan to insulate the floor too (between R19 and 49 - depending on insulation deals going on).

Replacement equipment: I'm looking at a single speed SEER 16 outside unit (want single speed because more efficient in terms of cooling then 2 speed) and looking at a 90k 2 stage variable speed furnace.

Also looking to get my house zoned (upstairs and downstairs zones) so my new equipment must be compatible with that.

If I were to have any HVAC problems it would be that the upstairs heats/cools differently (3degrees so) then the downstairs and it takes 6-8 hours for the entire house to cool off 2-3 degrees. Now I understand that 100 degrees is hot, but without humidity it should cool off faster. Also the amount of air out of the vents is pretty weak in from the upstairs vents.

So knowing that the unit works, is old, only SEER 8, what would you say to do first? outside unit and turn up the furnace blower motor speed, or furnace and let the variable motor take care of the work?
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Old 08-02-2012, 08:38 AM   #6
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Update Furnace or Condenser first?


Quote:
Originally Posted by rebelranger View Post
Ok I'll add some more to the story. The outside unit is 2.5tons and is nordyne, it's a 1992 Seer 8 model single speed. The furnace, natural gas, is a goodman 90k btu single speed 1990 80% one. It heats and cools my house fine, but is old and I would like to research/replace before I have to because then I'm paying the "I NEED NOW" rate.

Updates: I added attic insulation up to R49 (was R9 before), I added new triple pane low E argon filled windows (was wooden single pane before). Now I plan to insulate the floor too (between R19 and 49 - depending on insulation deals going on).

Replacement equipment: I'm looking at a single speed SEER 16 outside unit (want single speed because more efficient in terms of cooling then 2 speed) and looking at a 90k 2 stage variable speed furnace.

Also looking to get my house zoned (upstairs and downstairs zones) so my new equipment must be compatible with that.

If I were to have any HVAC problems it would be that the upstairs heats/cools differently (3degrees so) then the downstairs and it takes 6-8 hours for the entire house to cool off 2-3 degrees. Now I understand that 100 degrees is hot, but without humidity it should cool off faster. Also the amount of air out of the vents is pretty weak in from the upstairs vents.

So knowing that the unit works, is old, only SEER 8, what would you say to do first? outside unit and turn up the furnace blower motor speed, or furnace and let the variable motor take care of the work?
the first thing you need to do is perform or have a load calculaton performed for you so you can properly size the new equipment.

Here is a link to the one I used:
http://www.hvaccomputer.com/gtarget1...FQSFhwodPk4ANQ

Pay the $49 and do it right. My existing furnace was almost double what it should be.
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Old 08-02-2012, 08:50 AM   #7
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Update Furnace or Condenser first?


If it is hot upstairs, I would be looking at getting better ventilation into the attic space, along with those windows that are South facing, use a UV Film to help lower heat gain. As for your choice of equipment, with the added insulation, and any air sealing that has been done, like I stated before you could end up over sizing. I would do a Manual J to double check the numbers. Also zoning will raise the price of equipment.

Also depending on where you live, a heat pump may be a better choice than a a/c, and also where are you getting that a single speed 16 SEER is more efficient than a two speed?
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Old 08-02-2012, 09:25 AM   #8
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Update Furnace or Condenser first?


16 SEER single speed runs at max capacity and will achieve the set temp faster then a two stage 16 SEER condenser. The 2 stage unit is all about comfort, so 1st stage runs to remove humidity then 2nd stage runs to continue humidity removal while cooling. In terms of electricity usage a single stage unit running for 3 hours vs the 2 stage running for 7 hours, the single stage wins. I'm looking at pure electrical efficiency, and every HVAC tech I've talked to agrees but ALL say go 2 stage because of all the benefits in comfort it gives you. I want my AC to cool then shut off, fan recirculate the air and keep the house cool. I don't want my outside unit to run 8 house on 1st stage (although it uses less electricity) and not achieve the thermostat's desired results.

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