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Started By
Message
Are 2 central AC units the norm Now or is that specific to the application?
Posted on 8/17/21 at 10:14 pm
Posted on 8/17/21 at 10:14 pm
Single story 2500 sq ft 3 BR home. Internet says I’d need a 5 ton unit. So.. being a believer that
More is better, I’d be inclined to ask for a six ton unit. But would I be better with 2 each 3 ton units? Or is that set up for a two story home?
More is better, I’d be inclined to ask for a six ton unit. But would I be better with 2 each 3 ton units? Or is that set up for a two story home?
This post was edited on 8/17/21 at 10:15 pm
13
Posted on 8/17/21 at 10:16 pm to tigerinthebueche
quote:
So.. being a believer that
More is better,
Not in this case.
Lots of house specifics should also be considered like efficiency.
Posted on 8/17/21 at 10:25 pm to tigerinthebueche
I have 2 units (2 ton & 3 ton) in my 2800sf home. I like it because the bedrooms are on one unit and the kitchen/livingroom/etc are on the other. Also it’s important to realize more = better isn’t necessarily true when dealing with a/c. The manual j load calculation for my house called for 5 tons..I swore I needed more.. but my house stays comfortable and has no problems at all during the heat of the day.
Posted on 8/17/21 at 11:44 pm to tigerinthebueche
500 sq ft per ton is a very old rule of thumb from the 70’s and unfortunately still used today my many HVAC firms. It frequently over-sizes the system. More is definitely not better in HVAC unless you look forward to having a house with a short cycling HVAC, high humidity and associated mold and indoor air quality issues in a south LA climate.
Correct sizing of HVAC systems is correctly done via a manual J (heat and cooling load), manual S (sizing of the HVAC of cooling and heating system) and manual D (room by room sizing of the ductwork to accommodate the cooling and heating system).
I also have 2500 sq ft home single story, slab on grade, built in 93 (conditioned area) - a single 4 ton HVAC system. A manual J calculation indicates a 3.5 ton unit would adequate for cooling in my house - I believe it. Heating I have 96,000 BTU natural gas 80% efficiency furnace, manual J indicates 72,000 BTU 80% would suffice.
When my house was being built, the HVAC sub-contractor, used 2,500 sq ft as his cut for 1 or 2 units but the choice of 1 or 2 systems is yours, pros and cons to each. At times I wish I had 2 units, one for the bedroom wing and the other for the remainder of the house, but the single unit has served me well.
Since you mentioned it, I know from extensive reading numerous HVAC techs prefer separate systems for multiple story homes over singe units with zoning.
5-tons is the largest size HVAC made for residential homes. If a manual J indicated that more than 5 tons was required to cool a house at design temperature, one would need 2 units.
Correct sizing of HVAC systems is correctly done via a manual J (heat and cooling load), manual S (sizing of the HVAC of cooling and heating system) and manual D (room by room sizing of the ductwork to accommodate the cooling and heating system).
I also have 2500 sq ft home single story, slab on grade, built in 93 (conditioned area) - a single 4 ton HVAC system. A manual J calculation indicates a 3.5 ton unit would adequate for cooling in my house - I believe it. Heating I have 96,000 BTU natural gas 80% efficiency furnace, manual J indicates 72,000 BTU 80% would suffice.
When my house was being built, the HVAC sub-contractor, used 2,500 sq ft as his cut for 1 or 2 units but the choice of 1 or 2 systems is yours, pros and cons to each. At times I wish I had 2 units, one for the bedroom wing and the other for the remainder of the house, but the single unit has served me well.
Since you mentioned it, I know from extensive reading numerous HVAC techs prefer separate systems for multiple story homes over singe units with zoning.
5-tons is the largest size HVAC made for residential homes. If a manual J indicated that more than 5 tons was required to cool a house at design temperature, one would need 2 units.
This post was edited on 8/19/21 at 9:32 am
Posted on 8/18/21 at 3:20 am to tigerinthebueche
How tall are your ceilings ? It’s about air volume, not sq ft. Old way of thinking related to standard 8ft ceilings. Most new construction has 10 ft standard, with higher ceilings in various rooms.
Posted on 8/18/21 at 6:01 am to tigerinthebueche
More is not better
Posted on 8/18/21 at 7:52 am to tigerinthebueche
More is not netter. The unit cycles on/off too much and doesn’t properly condition the air.
If you go with one unit, position the plenum in the center of the house to minimize the length the duct runs to the rooms..
If you go with one unit, position the plenum in the center of the house to minimize the length the duct runs to the rooms..
Posted on 8/18/21 at 8:13 am to tigerinthebueche
Is this a new build I’m assuming OP? Big difference here? As said it’s better to have smaller units work all the time then one big unit rarely run.
Also consider the placement of the units. Newer higher efficiency units are not quiet. They are built for energy savings not sound. So if you are a light sleeper or otherwise have to put them next to the kitchen, living room, or a bedroom they may be noisy. Also, 2 units means potentially more floor space used unless you can put them in the garage.
2 units will also cost more and probably considerably more. But there are some benefits certainly such as redundancy.
Also consider the placement of the units. Newer higher efficiency units are not quiet. They are built for energy savings not sound. So if you are a light sleeper or otherwise have to put them next to the kitchen, living room, or a bedroom they may be noisy. Also, 2 units means potentially more floor space used unless you can put them in the garage.
2 units will also cost more and probably considerably more. But there are some benefits certainly such as redundancy.
Posted on 8/18/21 at 9:08 am to tigerinthebueche
We have 3 units on our house. A 5 ton for the main part, a 2 ton for the bedrooms upstairs, and a 2 ton for the MIL apartment. The MIL unit has had a few issues with electrical but all good overall. Our home is 8 years old.
Posted on 8/18/21 at 10:03 am to pdubya76
Great info guys! Thanks so much. I definitely will get a legit HVAC company when proceeding. To answer a few questions:
House was built 90/91. Currently has a heat pump which has performed very well and at a very low cost of operation. Ceilings are 9’ (estimated). Duct work appears to be flexible type, nothing fancy. I’m asking for advice and insight cause the heat pump isn’t getting any younger and I know that’s “old technology”. I’m just trying to get an idea of what kind of cost I’ll be looking at when the time comes. I do know everything is set up to put a normal AC unit in if I decide to get rid of the heat
Pump.
House was built 90/91. Currently has a heat pump which has performed very well and at a very low cost of operation. Ceilings are 9’ (estimated). Duct work appears to be flexible type, nothing fancy. I’m asking for advice and insight cause the heat pump isn’t getting any younger and I know that’s “old technology”. I’m just trying to get an idea of what kind of cost I’ll be looking at when the time comes. I do know everything is set up to put a normal AC unit in if I decide to get rid of the heat
Pump.
Posted on 8/18/21 at 11:39 am to tigerinthebueche
I have a 3100 sqft split floor plan. We have two 3 ton units and my electric bill is more than reasonable and the units are efficient.
Posted on 8/18/21 at 1:16 pm to tigerinthebueche
My house is almost 2600 sf and I have 1 system. Carrier infinity the largest one. I assume the variable speed helps a good deal with keeping the house cooler. My old house with single speed I had to set cooler to feel comfortable.
Posted on 8/18/21 at 1:20 pm to tigerinthebueche
quote:
I know that’s “old technology
dont know about all that... I am wrapping up my new build now and have 4 units I upgraded each to heat pump.
Posted on 8/18/21 at 1:22 pm to tigerinthebueche
As others have mentioned, the layout of the house would dictate more on whether to use a single unit or a pair. My house is a 2 story with a basement. The main air handler is in the middle of the house in the basement, and while it mainly cools the main floor, there is still some ductwork that goes to the upstairs.
A previous owner added a small heat pump for upstairs. It is nice to not run that during the day, because it is just 2 kids bedrooms, a bath, and a big open room in the middle. I have the thermostat set for it to come on around 7PM and run until around 10 so it cools it off before it adjusts up to a higher temp for overnight. It usually runs about 45 minutes to an hour before I hear it cut off, and it might click back on a time or two before the night shift starts.
My parents old house had two units, as well as two water heaters. They built new back in the early 2000s when I was off at school. My younger sibling was about to leave for college as well, so they built with this in mind. One wing of the house with only bedrooms, and a door they could close off. Dad would turn the air off over there and cut the water heater off when we weren't going to be home for several weeks. The kitchen, living room, laundry, den, and master were all on the other HVAC and water heater. And this was all in a single story home.
A previous owner added a small heat pump for upstairs. It is nice to not run that during the day, because it is just 2 kids bedrooms, a bath, and a big open room in the middle. I have the thermostat set for it to come on around 7PM and run until around 10 so it cools it off before it adjusts up to a higher temp for overnight. It usually runs about 45 minutes to an hour before I hear it cut off, and it might click back on a time or two before the night shift starts.
My parents old house had two units, as well as two water heaters. They built new back in the early 2000s when I was off at school. My younger sibling was about to leave for college as well, so they built with this in mind. One wing of the house with only bedrooms, and a door they could close off. Dad would turn the air off over there and cut the water heater off when we weren't going to be home for several weeks. The kitchen, living room, laundry, den, and master were all on the other HVAC and water heater. And this was all in a single story home.
Posted on 8/18/21 at 4:37 pm to tigerinthebueche
quote:
I’m asking for advice and insight cause the heat pump isn’t getting any younger and I know that’s “old technology”.
Heat pumps are not old technology, although they have been around for many years - still widely used around the country and recommended depending on circumstances.
Are you all electric or do you have natural gas to the house as well? If all electric a heat pump is a very wise choice. If the house is serviced by natural gas, then a conventional split system HVAC with natural gas furnace might very well be the better choice.
You are smart to be looking into this and planning your options now for an old system so you can have this figured out ahead time so you’ll know what you want and need if a “catastrophe” occurs and you need to replace the system rapidly.
I’m doing the same with a 15 year unit and will replace my system this winter. Ive been doing my homework on this subject for 3 years.
Posted on 8/18/21 at 9:19 pm to tigerinthebueche
quote:
House was built 90/91
It’s going to be a lot cheaper to keep your current set up then do any sort of major reconfiguring. 1 units to 2 or 2 units to 1 being major.
Posted on 8/19/21 at 10:22 am to baldona
quote:
It’s going to be a lot cheaper to keep your current set up then do any sort of major reconfiguring. 1 units to 2 or 2 units to 1 being major.
Sort of depends on access. Where is the air handler currently, is there any basement/attic space to install another if wanting to go to 2 units. Previous owners of my house were able to easily add a heat pump with the air handler in the attic off the second floor. Ran flex ductwork to the 2 BR and one room in the middle. When we had our main unit replaced last year, all the work was in the basement, and moving the outside unit out from under the deck. If you're not trying to run lines and ducts through existing walls, the labor part will be much less.
Posted on 8/19/21 at 11:34 am to TU Rob
My heat pump is in the attic and draws water from a well next to the slab. It’s centered over the master bedroom. Again, it’s been great as far as performance goes. Everything is upstairs in the attic.
Except the thermostat
Except the thermostat
Posted on 8/20/21 at 7:03 am to tigerinthebueche
Also a good backup when one has issues. At least you can go sleep in another part of the house for a day or two.
Posted on 8/20/21 at 9:50 am to ColdDuck
quote:
Also a good backup when one has issues. At least you can go sleep in another part of the house for a day or two.
That has saved us a time or two. When the main unit wasn't cooling several years ago, I left the fan on it running and we turned on the air upstairs. Throw a cheap oscillating fan in our downstairs bedroom for us to sleep in, and if it got too bad down there we could always throw sleeping bags on the floor for the kids and take one of those beds.
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