Adding AC to old house

[robert_kc]

I’d appreciate any advice about adding central AC to the upstairs of my old house. What should I require contractors to include in their bids?

My primary goals:

• Quiet operation, so that I can enjoy listening to music in summer. (Any ideas on how to minimize noise?)
• Minimal impact on aesthetics in living space. I prefer not to have indoor wall mounted units (e.g., associated with mini split system). Ceiling vents or cannisters are preferable.

Should I install a traditional evaporator coil in attic, with insulated duct-work to each bedroom?

Or, a mini-split, with ceiling mount cassettes, or “horizontal ducted”? Mitsubishi? Other brand?

Variable speed compressor? Inverter technology?

Here’s some information about my house:

Kansas City
Built 1925
The attic is unfinished
Currently no ductwork. Home has boiler / hot water heat (radiators). Never had central AC.
Stucco exterior. Lots of windows.
Plaster and lath walls. (No insulation in walls).
Upstairs: 3 bedrooms, bath, hall.

• Total: 720 sq ft upstairs
• 8 ft ceilings
• 5760 cubic feet

Distance between top of windows and crown molding: 8” (Not enough for mini-split indoor units that I’ve read about.)

Dehumidify bathroom. Return vent in bathroom? Exhaust fan?

(Current plan is for downstairs to retain window-AC unit that is built into wall.)

Thanks for any suggestions about what I should require contractors to include in bids.

 

[onwardjames]

Both my good friend and the place I work have those ductless AC's. Gotta say I am VERY impressed. No loss of cooling from the ductwork. Worth a look.

I know that when I build my forever home, that's how I'm doing it.

 

[wlhd1610]

We built a new YMCA a few years back .
They spec'd a Sanyo mini split for the office that had the air handler above the drop ceiling using traditional ductwork/registers.
The variable speed condenser was up on the roof.
Very nice ,compact and quiet.
All you really have to figure out is where to run the evaporator drain line to.

You can put the air handler in the attic and the condenser either on the roof (if flat) or down on the ground.

Bob

 

[sKiZo]

Another vote for mini-split. I put one in a couple years back for the bedroom and it's quiet and does a nice job. I wouldn't think the distance from the top of the windows to the ceiling would be an issue ... you can mount the inside unit on any available wall as long as there's a place to run the power and coolant lines.

Worth mentioning (and I'm sure any HVAC pros here will cringe) I installed it myself. Both the AC units and lines came pre-charged, so just burp it a bit after hooking everything up. No problems here anyway.

PS - mine is a 12K Soleus heat pump. Outdoor compressor, inverter, variable speed, and has the new 410 gas. Also runs on 120v, so no special wiring required as long as the line can handle the amp load. I'm cooling about 800 square feet. Also handy for winter to warm the bedroom if I get to bed late after the central heat goes into "sleep" mode for the night.

 

[robert_kc]

Thanks for sharing information.

The compressor would be mounted on the ground outside. The air handlers (evaporator coils) would be in the attic. (Two story house.)

The AC system would serve 3 bedrooms upstairs. It appears that the choice is between a single “traditional” air handling unit with ductwork, vs. a “ductless” mini-split system.

I found this description of a ductless AC system: "Ductless systems pump cooled refrigerant directly to wall or ceiling mounted air handling units through small lines. Each room or living space has its own air-handling unit and each unit has its own wireless electronic temperature control system." (I don’t like the appearance of the wall mounted indoor units, so I’d want ceiling mounted. Apparently Mitsubishi calls these “ceiling cassettes”.) Presumably these ductless systems have the benefits of controlling the temperature separately for each room, and less loss due to ductwork. Correct?

I’m curious how water would flow out of the 3 ceiling mounted cassettes? A pump? (If I understand correctly, the cassettes would be sitting on the floor of the attic (on top of the bedroom ceiling), so there’d be no downward angle through the attic to the back wall – i.e., no gravity flow.)

OTOH, are there any benefits associated with a single “traditional” air handling unit with ductwork? Would it be quieter? Could the air handler (A coil) be suspended from the rafters, rather than sitting on the attic floor – potentially minimizing vibration transmitted through the ceiling? Lower cost because there’s a single air handler / evaporator coil / fan?

The bathroom is small (5 x 9). What’s the best way to deal with steam from the shower? Exhaust fan? If I install a ductless AC system, should I install a ceiling cassette in the bathroom? OTOH, If I install a traditional system with ductwork in the attic, should I simply put a return vent in the bathroom to pull the steam out of the bathroom (relying on the AC system to dehumidify it)? This bathroom has existed for 90+ years without an exhaust fan, but if I invest in a central AC system, it might make sense to deal with steam from the shower.

Thanks again for sharing your experience.

 

[gadget73]

The big question is do you already have ductwork in place. If yes, maybe a conventional split system makes sense. If not, mini split is the way to go. Running ductwork in a house that doesn't have it is not a simple or cheap task, and depending on the construction of the house it can be a real nightmare.

 

[Lo-Fidelity]

I purchased and installed a ducted Pioneer mini-split for a garage apartment. Can't stand the look of the in room units that are standard for mini-splits. It works well, but probably a little under sized. I was concerned about controlling humidity so I erred on too small versus too large a unit. It will not quickly cool down the space so I just leave it set within a few degrees of where I want it. It is so quiet you don't know if it is on or not. You have to go outside and see if the compressor is running. Humidity control is excellent. The apartment has good insulation, but very old and leaky windows and doors.

 

[robert_kc]

I thought I’d share my experience with adding central AC to my 90+ year-old home.

Here’s a recap of some information about my house:

• Built 1925
• Two story. Unfinished basement. Unfinished attic.
• Originally no ductwork. Home has boiler / hot water heat (radiators). Never had central AC. (I’ve been using window AC units in this house for 33 years.)
• Stucco exterior. Lots of windows.
• Plaster and lath walls. (No insulation in walls).
• Upstairs: 3 bedrooms, bath, hall. Total: 720 sq ft upstairs. 8 ft ceilings.

I installed the top-of-the-line Lennox Signature Series XC25 outdoor unit, and CBA38MV-018/024 air handler. 2 ton rating.

The CBA38MV-018/024 indoor air handle features multi-speed operation via an ECM (Electronically Commutated Motor), Lennox Quantum™ Coil, 10 kW heat strips (which I had installed for backup in case my boiler fails), and Merv 16 filter. Lennox claims: “The CBA38MV is the industry's most quiet and efficient air handler, providing reliable comfort, more consistent temperatures, and enhanced humidity control in all types of environments.”

The XC25 outdoor unit is described as a variable-capacity air conditioner. 26 SEER. Lennox claims: “The XC25 is the finest air conditioner Lennox makes, and one of the main components of the Ultimate Comfort System™. The most precise and efficient air conditioner you can buy.”

iComfort® S30 Ultra-Smart Thermostat.

The outdoor unit was installed on a pad on the ground behind the house. The air handler was installed in the attic (suspended via unistruts), with ductwork feeding rooms upstairs, plus one duct is installed through an upstairs closet to a vent in the downstairs dining room. (This is the only upstairs closet that is aligned above a living space downstairs, and therefore the only convenient location for a duct feeding the downstairs.) A large duct is at the top of the stairs, dumping cool air down the stairwell. A single return vent in the upstairs hallway. All wiring and pipes were routed from the attic through a laundry chute to the basement. The drain line goes to a floor drain in the basement. The refrigerant and power lines route across the basement, through the rim joist to the outside unit.

(An alternative that I investigated was installation of a ductless mini-split system with ceiling cassettes in each room upstairs. (I refused to consider the ductless mini-split wall-mounted units due to aesthetics.) All five contractors that I spoke with declined to propose such a solution, because large holes would have to be cut in the ceilings, and the holes would have to be framed-in for the cassette units. All contractors recommended the traditional air handler installation described above instead of a mini-split system, and therefore that’s what I contracted for.)

A top-of-the-line Panasonic bathroom exhaust fan was installed above the shower in the upstairs bathroom to help with humidity control. It is vented through the roof. (I don’t know why AC contractors refuse to do this work. My electrician installed the bathroom fan.)

After the AC system was installed, I had insulation added to the attic, including foam and seal of attic floor penetrations (e.g., wires, plumbing, HVAC boots), and insulation was sprayed onto the rim joist in the basement.

I had to upgrade my electrical service from 100 amp to 200 amp in order to install this new AC system (with heater strips).

When the outside temperature is below 92 degrees, the AC fan runs (automatically) at a low speed, and I cannot hear it run.

When the outside temperature is over 92, the fan runs (automatically) at high speed for most of the day, and I can hear it running. In response to my complaint about the noise, a technician adjusted the maximum fan speed down somewhat, which reduced the noise when the fan is running at its highest speed. Currently on hot days the AC system can be heard running at what I would describe as fairly loud - not obnoxiously loud – but not nearly as quiet as when the outside temp is below 92. I’m somewhat disappointed in this. (The highest temp we’ve had thus far this spring is 96.)

The system is able to maintain the indoor temp at 73 when the outside temp is 96. Given the fact that it must run on high for 10 – 12 hours when the temp is 96, I’m somewhat concerned if the system will be able to keep the house cool when the outside temp is over 100. Time will tell.

Because the system runs anytime it’s hot outside, and automatically adjusts the fan speed and compressor, the indoors is (thus far) always uniformly comfortable. No fluctuations in indoor temperature. No room-to-room temperature variation.

Downstairs I’ve retained a window-AC unit that is built into the wall in the breakfast room. Generally, I don’t need to run this downstairs widow unit. (I ran the downstairs window AC one day when the outside temp was 96 and I had 6 people in my living room.)

Overall the installers did a good job, except for two issues.

The installers had to cut holes in the plaster ceilings. One issue I didn’t anticipate, and therefore didn’t include in the Statement of Work, was sealing the ductwork boots where they come through the ceiling. After the installers left, I removed each register, and used backing rod (where needed), two applications of caulk, and 2” aluminum tape to seal the boots. If I had it to do over, I would have specified that the contractor complete this work. (My concern is about dirt from the attic (and unconditioned air) getting into my home.)

The installers initially used zip ties to suspend the flexible ducts in the attic. This pinched the flex ducts, and at my request the installers removed the zip ties and used wider straps.

I did not make this investment expecting a payback from energy savings. While it will be interesting to see if I have lower energy usage this summer vs. the last 2 years (using window AC units), there is no way that my total investment will be repaid based on energy savings during the lifetime of the system.

Thus far I’m satisfied. Compared with window AC units, my house is more uniformly comfortable, and quieter (particularly when the fan is running on low). If the system can handle 100+ degree heat, and it works reliably for a number of years, I’ll be happy with the investment. I invested considerable money and time (defining requirements and coordinating contractors) to make these upgrades to my home. Considering that we’re having record high temperatures before summer officially begins, I’m glad I made the investment.

 

[Lo-Fidelity]

Nice system. I’d be shocked if you aren’t very happy with the performance and reduction in the electric bill. How is the humidity control. Here in the Houston swamp that is critical for comfort.

 

[robert_kc]

The iComfort® S30 Ultra-Smart Thermostat has a menu section called Dehumidification Control Center. End-user controlled settings include:

• Normal
• Max
• Climate IQ (Auto)

You can also set the "dehumidification set point" and the "overcooling range".

The inside air handler has a variable speed fan, and the outside AC compressor has variable capacity, and when outside temps are warm the AC runs all of the time - at automatically varying speeds. This keeps the air inside the house circulated, and constantly dehumidifies. The inside of my home is consistently very comfortable.

As I type this at 11:30AM, the outside temp is 87. The AC system is so quiet I can't hear it. I know its running because I can look out the window and see the fan on the compressor turning, and if I hold my hand near a vent I can feel cool air gently blowing out. Today the forecast high is only 89, so the AC system will probably never run on high.

Based on my experience living with this system for 6 weeks (with record high spring temperatures), I predict that next week when the high temps are forecast for upper 90s, the system will run on high from approximately 11:00AM to 7:00PM - then it will gradually ramp down until its running on low by 10:00PM.

 

[gadget73]

Something you do get from something that runs more is better humidity control. I expect overall it uses less power or they wouldn't do it, but it certainly improves the comfort. That is one thing I do miss about the dinosaur AC we used to have. It was tired and almost never cycled out, but boy did it do amazing things for humidity control running basically 24/7. The power company absolutely loved us too, the money it cost to run a 35 year old AC constant for an entire summer was significant.