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Heating & Air Conditioning

Do I replace my HVAC duct with a new furnace/condenser?

4 years ago

Hello All

I am doing a whole-house renovation now, so opening some walls here and there. My contractor replaced the furnace and condenser in the house. The furnace is located in the attic, while the condenser is located on the balcony on the 1st floor.

The old furnace/condenser were both about 30 years old. I am not sure if the duct has been replaced but I assumed no.

Should I replaced the duct in the whole house? My contractor changed the duct in the attic and mentioned that the duct in the attic is the most important as there is large heat fluctation in the attic. He checked the duct through the house and said it's still in good condition with good insulation. He also mentioned that duct last a very long time.

I assumed when you replaced the HVAC system you would want to replace ALL the duct work? Should I replace it? Is he right? Thoughts?

My thoughts are given that I am renovating now, I should just replace it. My contractor thinks it's a waste of time.

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Comments (6)

alanfong31
Original Author
4 years ago
Sorry I meant my contractor thinks it's a waste of "money".
fsq4cw
4 years ago
Are the ducts sized to deliver the volume (CFM) of air required; do the leak?

SR
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So, if I do not use bleach to clean the drain, how to you recommend that I should keep them clean? One way: use a good quality filter and change them at regular intervals. This method is not perfect. Second way: pitch drain line to a minimum 10-15 degree angle so that it empties fully, into a single trap if possible --- trap placement is just as important. Flat piping runs and elbows should be avoided as much as possible. (Don't forget about first step.) IE: gravity works for you just as much as it can work against you. It all comes down to the design of the drain system. Third way: wait until it clogs and then clean it out / or pay to have it cleaned out. Which way do you suppose most service companies are counting on? So by now you clearly see the 'two sides to every coin'. If something is billed as being perfect --- it is an out right lie, merely to swindle you. Drain line could still clog given the second way, but you cut the risk to fraction of what was possible with other methods. It's not always possible: architecture was built for beauty, not for how the HVAC system condensate line is to be run to prevent drain clogs. In some situations it may be better to level the home and start over. Ah the reasons why someone sells a home these days... it will boggle your mind. It should be noted that bleach does not clean the drain, it merely treats it by killing bacteria and algae growth. To keep bacteria and algae growth in check the drain has to be treated continually, because as you run the AC the bleach is eventually diluted and flushed down drain with condensate from the AC. The problem with retreating is that bleach is corrosive. If not flushed down the drain completely the fumes come up the drain and attack anything metal. Your all aluminum coil is no match for bleach. It will attack the heat exchanger as well. The more you treat the drain with bleach the more less likely you have drain clog, but at the expense of system damage due to the corrosiveness of the bleach you use to treat the drain.
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weedmeister
4 years ago
" I assumed when you replaced the HVAC system you would want to replace ALL the duct work "

Bad assumption. There's no reason to replace all of it if it is in good shape. The only question might be about the insulation value of the covering. And if any of the joints need resealing.
fsq4cw
4 years ago
weedmeister

" I assumed when you replaced the HVAC system you would want to replace ALL the duct work "

Bad assumption. There's no reason to replace all of it if it is in good shape. The only question might be about the insulation value of the covering. And if any of the joints need resealing."

Not necessarily so, if installing a HP where previously there was only a forced air gas furnace, oil furnace or all-electric furnace that delivered a higher temperature heat, you might want to replace duct work that is too small to deliver the volume (cfm) of air now required due to the much lower temperature output of a HP.

Having improperly sized ductwork will lead to complaints about uneven heating, being cold in heating mode, drafts and noise.

IMPO

SR
PRO
Austin Air Companie
4 years ago
last modified: 4 years ago
Given that you're renovating I would say it's a good time to do it. It can raise the costs dramatically depending on a myriad of factors.

If what you have is flex duct / going back with flex duct the costs shouldn't be too extreme, but this can lead to boot replacement and vent replacement so that can increase costs further than just duct work alone.

You should replace with at least R8 flex duct if you are going back with flex. This can pose challenges because circumference wise these ducts will be larger than what you have now most likely.

By using a minimum R8 insulated flex duct, this will increase the efficiency of the system, marginally in most cases depending on climate. It also wouldn't be a bad idea to possibly add an additional new filtered return at a known hot spot / cool spot within the structure. (hot or cool --dead air space that might be getting trapped, by adding a filtered return to this spot it will aid in the comfort factor of the structure.)
User
4 years ago
Is your contractor a licensed HVAC professional? If not, did he bring one in to replace the units and ducts in the attic? If the answer is no to either question, it’s time for the contractor to admit he’s out of his personal depth and get a real expert out there to assess the original system of ducts and it’s condition and compatibility with the replacement system.

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