HVAC installation and Duct-work?

I'm in the process of shopping to replace my HVAC - at present I have a Furnace only but interested in adding AC. I've had a couple of bids done by local companies and trying to figure out which to trust/go-with.. One of the main differences in the bids i've received is reg'd the duct-work in my house. The existing ductwork was replaced during a large remodel around 2008 - so they are about 15 years old. My house is approx 2000 sq ft, and is located in coastal Southern Calif. In this area I've survived without the AC for a while but it'd be nice for about a month out of the year (i already have a whole house fan which is great most of the time).

Company A - Lennox ML17XC1 - 3 Ton AC, Lennox ML180V Furnace .. NO Ductwork required
Company B - Bosch BOVA-36HDN1-M15G 3 Ton AC (inverter condensor), Rheem R801T0754A17UHNNAS Furnace.. FULL replacement of 5 duct runs

Given similarly sized AC units, any thoughts on whether the duct-work is really needed on the job? Does the addition of AC usually require larger ducts?

thanks in advance

 

First, contact the contractor and have them explain why they want to replace the ducting. Maybe they saw or know something we don't.

It is hard to offer advice since we don't know your house or it's ducting. So, anything is largely a guess. But, I had many rental properties and averaged replacing 2 or 3 HVAC systems per year. It was extremely rare to need duct replacement. When it was done it was due to the old ducts being damaged, and it was pretty obvious that they needed replacing. If your ducting is in good condition I would want a very good reason for why it needs replacing.

 

Thanks Dane - these bids came from local companies that specialize in HVAC.. I inquired with both of them about the ducts.. Of course, the one requiring newer/larger ducts (and vents) indicated that the following:

Your existing ductwork is undersized for AC so my plan is to enlarge the one in the master bedroom, the two in the living room and the two in the ADU. The rest of the ducts would remain.

So basically he is requesting to upsize a subset of these ducts/vents. The master bedroom has 1 vent approx 13.5"x7.75" .. The living room area is actually more of a great room combined with my kitchen.. For this whole area there are a total of 4 vents - 2 near kitchen and 2 in living room.. All of these are the same size at 13.5"x7.75". His recommendation was to upsize 2 of the 4 in this great room

The company which did NOT require any ducting for the system told me the ducts are in great shape and didn't see any need to change them..

 

I am not an HVAC tech so take what I say with a grain of salt.

It looks like the Lenox quoted is a simple single stage AC. That's appears to be a basic unit and is probably more forgiving of a slightly undersized duct. The Bosch is a variable speed Heat Pump and would be capable of providing both heat and cooling. Because the Bosch is a variable speed heat pump able to run at 110% capacity might be why that installer also wants to upgrade the ducting. So, they are very different units and it's like comparing apples to oranges.

 

Gotcha - thanks Dane .. FWIW I did also get a quote from the 'NO Duct-needed' contractor for a non-name brand inverter-style system like the Bosch - does both heating and cooling - ACPRO AULD36W2 (3 ton) . Guessing it isn't exactly the same as the Bosch unit but similar.. Anyhow, they weren't asking for Duct work for this setup either