A/C gone bad

[gusherb]

I'd bet 3.5-4 ton would be more than enough for that house. I'd be looking at the ductwork, particularly the return air to make sure it's not undersized, that will always make an oversized system perform like it's undersized. I believe a 5 ton system should have at least 2 18" returns.

13 years ago when I did our upstairs system, it was practically unheard of for contractors to offer Manual J here. I went with the one that did, but he fudged the numbers so much in the software that we ended up with an oversized system anyway.

Second time around, 8 years ago, I solicited bids again for the downstairs system and everyone was offering Manual J. I ended up going with the contractor who wanted to downsize our furnace from 100k to 60k, we kept the same 2.5 ton condenser as that was already sized correctly. The furnace has no issues keeping up and it runs nice LONG cycles in 1st stage and 2nd stage doesn't kick in until it's below 10º outside.

 

[DADoES]

 
I have two 20" x 25" (grill/filter size) returns.

Second quotes.  Single-stage 15 SEER Trane (4TWR6060H1, TEM6AOD60H, 81-0703-01), $10,216.73.  Two-stage 17 SEER (4TWR7060A1, TEM6AOD60H, 81-0703-01), $11,718.27.  Does not state if sales tax is included but I assume not.  It is included on the first quotes.

 

[gusherb]

I'm not sure about your market plus things being the way they are lately, but those prices around here for a simple changeout seem kinda high. That said, that 17 SEER two stage quote isn't a whole lot higher, I'd be tempted to go that way but I'd downsize it to 4 ton. Was there ever a time when your 5 ton would run continuous to maintain setpoint or even not keep up? A proper sized system would run continuous at design outdoor ambient (which IIRC is around 97-102º depending on which part of TX) with an indoor target of 75º.

 

[chachp]

July 2020

 

<span style="font-family: helvetica;">Our A/C went out and we decided to replace the entire system because it was 18 years old.  The Heat Exchanger and Compressor were replaced around 2014ish from what I could find in the paperwork.  The system is Trane with a 16 SEER 4 ton compressor and a two stage furnace.  All in it was $7318.20.   We put a two stage in the old house and really loved it so we went with the two stage here as well.  I don't recall the difference in price.</span>

 

<span style="font-family: helvetica;">We had an interesting situation in this house.  It's 2400 sq ft. and the family that built this house had a zoned system put in.  It didn't make a lot of sense because one zone was most of the house and the other two zones were each of two smaller bedrooms at the other end of the house.  That needed to be replaced or removed when we put in the new system.  It would have been about $2,000 to replace or $800 to remove.  Since it didn't really buy us much in this house we had it removed.  We paid the $800 to have them remove the unneeded ductwork in the attic and air balance the system.  No regrets.</span>

 

[gusherb]

Zoning forced air is usually an act in futility getting it to work right, particularly when they’re small zones like that. And it murders your systems efficiency. The only way it works is if each zone can individually handle the full airflow that the equipment requires, or if it’s two stage and each zone can individually handle the airflow needed for the 1st stage. Or if it’s a communicating zone system like Carrier Infinity or whatever Trane calls their version where it can adjust the blower CFM according to how many zones are calling, and it all works even better if you’re using a modulating furnace and modulating inverter condensing unit.

 

[whitewhiskers]

no fan of zone control

I have a Honeywell Zone Control System, three Honeywell Modulating Automatic Round Dampers (MARDs) and a Honeywell Universal mini-zone controller box. It's been problematic since day one. The primary problem are the MARDs. All dampers move to the open position when the system is off. Depending on which zone calls for heating or cooling causes some of the MARDs to close. The dampers are prone to sticking or they leak air. The zone controller developed cold solder joints causing all kinds of erratic behavior. I reflowed several connections years ago and no problems since.

Had the original installer out twice to fix the leaking air problem. The result was the tech fried one of the zones on the controller board. Moved the zone to an unused port but now have no spare. Right now I'm sure all zones blow air even when one of the zones should be closed. I gave up on the system years ago. In theory zone control sounds good, but in practice you will be buying a constant source of problems.

 

[retro-man]

I have 2 heating and a/c systems in my house. The 1st is in the basement, there is one zone down there and the 2nd zone does the 1st floor. The 2nd unit is on the 3rd floor. 1st zone is on the 2nd floor and the 2nd zone does the 3rd floor. They were installed 15 years ago and no problems with the zone features on either unit. Also had both systems balance for airflow when installed and all rooms in all zones keep target temps set. Very please the way they work.

Jon

 

[chachp]

Zoned systems

 

<span style="font-family: 'American Typewriter', serif;">We have had zoned systems in the past and have been happy with them but in all those cases it made sense.  The man who built this house was a contractor who built this house for he and his wife who had become empty nesters.  His daughter said since he was a contractor, he had access to lots of cool upgrades and added the zoned system just because he could.  The house is filled with many upgrades that make sense but this one didn’t.  It’s 2400 sq. ft. with large rooms except for these two small bedrooms at the opposite end of the house.  They zoned the entire house as 1 zone and then each of the two small bedrooms were a separate zone.  It worked as designed for a while, but we started having issues with damper motors as it was 18 years old.</span>

<span style="font-family: 'American Typewriter', serif;"> </span>

<span style="font-family: 'American Typewriter', serif;">If we could have easily made the Master Bedroom and Bathroom a separate zone then we would have replaced the zone system along with the new A/C and furnace.  With this setup we could heat/cool just the bedroom at night vs. the entire house, but the way the ductwork was done it would mean ripping out what was done on that end of the house and redoing it.</span>

<span style="font-family: 'American Typewriter', serif;"> </span>

<span style="font-family: 'American Typewriter', serif;">So, we made the decision to remove the Zoned system altogether and have been happy with it.  I think it depends on the brand and how the system is designed.</span>

 

[jamiel]

We are contemplating putting in a small split system for the upstairs---currently we struggle to get the upstairs (2 story Colonial house, all 3 BR upstairs, black roof) cool enough on a hot (>85) day...doesn't happen often in Michigan, but just enough to be a pain.

 

[chachp]

Split System?

 

<span style="font-family: helvetica;">I don't know what a Split System is but here in the South if you have a two story home you really need two separate systems to cool the upstairs.  My condo complex when I moved here in 2002 was built in two phases.  They were all two story units, bedrooms up.  The first Phase was built with 1 system for the entire unit.  The second Phase (where I was) was built with two systems one up and one down.  The people in the old Phase did nothing but complain about cooling the upstairs.  The complex didn't allow for air conditioners in the windows so it was an issue for them.</span>

 

<span style="font-family: helvetica;">Since then both houses we've had have been single story, LOL.</span>

[this post was last edited: 11/12/2021-12:44]

 

[48bencix]

1946 Ranch House

I moved here in 1990 into a 1946 Ranch with 1960 bedroom and family room additions. One window unit in the family room really did not cool the whole house. I designed and installed a new system with the gas furnace outside the slab on grade family room and ducts into the attic for the rest of the house. (Built a small outside enclosure for the unit) Components such as condensing units were available at the time for a homeowner, now only to contractors. I hired an HVAC contractor to connect the condensing unit and add any charge required.

Fast forward to 2017 and I decided to replace the furnace and condensing unit. Had a contractor install Trane units and permit required testing of all existing ductwork. Leakage was less than allowed for new ducts, so my original ducts system was passed. Old SEER was 11 new is 14 with 80 AFUE for the furnace. Better efficiency but not really high efficiency as I believe this will be more reliable. Contractor provided a 10 year parts and labor warranty. I serviced the old units myself mainly changing the furnace igniters and run capacitors in the condensing unit. With the ranch style no need for zoning. We did insulate the walls (no existing wall insulation) and added attic insulation.

 

[bradfordwhite]

Ten's of thousands for a stinky, noisy, overly complicated and unreliable ducted systems?! I'm literally shocked and appalled what contractors are charging. But with (supposed) labor shortages....maybe they feel they can get away with it.

No way would I when you can get pre-charged mini-splits for under $500.

Videos online showing how to install.

The onslaught of legit competition is most likely what's pushing the prices for the old fashioned ducted systems. It's just like with the old fashioned auto prices going sky high, now that Tesla and other electric vehicles have arrived.

https://www.ebay.com/itm/1650371621...DttQAhnQJHFks0%2FL5dH96FfXuhnr%2Brs0xhGSc%2Br

 

[bradfordwhite]

And if you want zones on the same system

I wouldn't do zones but each their own.

https://www.ebay.com/itm/3027412711...Uc8c1O2BsfuNXqi5HW%2BBKu9k4bVvIPPIe2qPK2ndj3i

 

[DADoES]

 
Both of the HVAC outfits said they'd do a Manual J.  One I asked directly, the other's office girl said without prompting that they'd come onsite and "measure windows & stuff" for the quote.  Neither did so.  Both are referencing the "rule" of 1 ton per 500 sq ft.

Plugging my measurements and parameters best as I can determine them into the online load calculator at http://www.loadcalc.net using its default design temps for this area of 94°F/75°F/50% and 33°F/70°F says 21,831 BTU (1.8 tons) cool and 38,895 BTU (3.2 tons) heat.

I run 78°F to 79°F during heat of the summer, never 75°F.  A bit cooler for humidity control during fall & spring when needed but rarely even to 74°F.

Changing to 102°F/77°F/50% and 30°F/68°F gives 25,705 (2.1 tons) and 39,946 (3.3 tons).

I had a follow-up call yesterday with the Trane outfit to ask some questions, including for a 1-speed 4 ton quote.  Guy said reducing to 4 tons wouldn't be a good idea.  Figure how he's likely to respond if I tell him the online Manual J says 2 tons cooling is sufficient (although it does say 3.5 tons for heating without auxiliary).

 

[bradfordwhite]

A heat Calc

I had to have a heat Calc. done on the last house I built.  These days most building permits require them as part of the permitting process.  It's really a good idea since there are many variables that affect equipment sizing and options.

 

[sudsmaster]

Is anyone in the northern hemisphere still runnning their air conditioning system in November?

Note: the only AC system I have is a small ~5000 btu window unit that I took out of the house about 10 years ago, and a somewhat larger (~10000 BTU) roll around unit that I can roll up to a window (usually in the combined family room/kitchen area) that I didn't have to roll up to a window and run at all this past summer.

Gotta love the SF Bay Area.

Oh, and the forced air gas fired heating system didn't start coming on until November here. And then for only a few minutes in the evenings. Although I expect more heating will be needed in the coming weeks/months.

 

[DADoES]

 
Cooling in November .... yes.  It was in the mid 80s and humid a couple days ago before the latest norther arrived.

Have been instances of cooling during a Christmas warm spell.

 

[qsd-dan]

Glenn is located in the south where temps can exceed 85F beyond Thanksgiving day with high humidity.

 

[chachp]

Reply 31 and Reply 32

 

<span style="font-family: helvetica;">We were still cooling until last week...ish.  We are now in the 60s but back to mid 70s this week so I expect we will be cooling again.  </span>

 

<span style="font-family: helvetica;">We see a lot of units like those split units here in older homes (we are estate sale freaks so go into a lot of houses) that never had central air.  We also seem to see a fair amount of them in two story homes where they had one unit for the entire house but then added some of these to have effective A/C upstairs.  My guess is it would be cheaper to put these upstairs than it would be to convert ductwork from a single unit to multiple units.  Any of the experts know if that's a true statement? I am only guessing based on what we see.</span>

 

<span style="font-family: helvetica;">Most newer homes built here that require multiple units seem to have the traditional central air units.  Maybe these split units are cheaper to put in, I really don't know.  We were in a house a couple of weeks that was a really cool MCM house.  They had units like this with louvers that rotated back and forth I guess to distribute the air better. </span>

 

[gusherb]

The only way I would go with mini splits is if it was an older home that I couldn't feasibly get ductwork in without ripping too much of it apart, or if I had a specific area that needed cooling. My neighbor built a room addition with radiant floor heat and used a mini split for cooling, which made the most sense.
Those systems can quickly reach or exceed the cost of a conventional forced air system, especially if you're using higher quality brands like Mitsubishi Mr Slim. Conventional forced air if designed properly is more discrete, costs the same or less than mini splits, and has less electronics to fail on the equipment.

Interestingly, I see a trend of people ripping out hot water or steam heating systems and putting in mini split heat pumps on the east coast. Those people probably wonder why their house suddenly feels draftier after doing that...