Normal… Zoning the return
Normal… Zoning the return would accomplish nothing!

On paper, return air will naturally pull from the calling zone since zonal pressure imbalances in a closed system can only be transient (momentary). In reality, a portion of the return air may be pulled from the non-calling zone due to influences of exhaust fans, clothes dryer, atmospheric furnace or water heater, infiltration and/or exfiltration, etc. But none of this has much of an affect, if any, on supply air distribution.

Maybe growing up in that house I just assumed zoning was the norm. It always puzzled me why it was not more common when I got out in the world. Like sealed crawl spaces and spray foam ..zoning requires time and figuring — it’s easier to use some common formula and install what you did down the street.

With today VS equipment there is no reason not to zone ,,,, in fact since most ductwork is undersized it can actually help make problem houses more comfortable.

My last two projects have used the Carrier 5 speed HP w/ VS air handler. The new systems actually run tests on the ductwork .. slick. The biggest problem is getting the HVAC installer to do a proper room by room heat and cooling load — figure out what ducts are required for those numbers … believe them, and size the unit to the figures. Most don’t. The only other odd item is to size any zones duct to 25% above the lowest CFM of the unit. Most times if the unit is sized correctly — the unit works out without any additional thought. Basements with low loads can sometimes be close. The new units modulate away all day .. moving air around. It’s very rare for us to have the whole house at the same temp — why try and cool the second floor to a constant 72 all day when no one is there ? Allow some natural heat rise and cool it down later when the system can easily do it with no heat gain.

Yea, David, I am talking
Yea, David, I am talking about zoned systems done poorly which is most of them from my experience. I think that zoning dampers should never be added to a single-capacity system, even if it has a variable-speed blower. Bypass dampers should never be used. Dump zones are bad too.

Third-party zoning control companies claim energy savings and better comfort. I agree with you that zoning is and should be primarily done for comfort. Turning off unused zones makes sense from an energy perspective, but as you point out, it can cause other problems.

I believe that the solution for high-performance homes is a small ducted system. I would push for a 1 to 1.5 ton ducted system with one system on each floor of a two story house. The air handler and ducts would be small, easily hidden, and in the conditioned space. I am not even sure if it needs to be variable capacity. This type of system would be cheaper than current mini-splits and not require plastic boxes hanging on walls and would still allow air supply to bathrooms and large closets. There is hardware available today for doing this, and if the concept became widely used, better and more cost-effective hardware would become more widely available.

The multi-sensor thermostat is starting to become more popular today, but for the wrong reason. Electronic thermostats with big color screens and lots of bells and whistles just can’t sense temperature accurately, so they have to go to a remote sensor. Adding multiple remote sensors is then an easy option, and selective zone control becomes a “free” option.

Sounds like your analogy is
Sounds like your analogy is directed at zoned systems done poorly? I certainly can’t argue with that. But a zone system designed to work within the operational range of the blower and compressor, using integrated OEM controls (as you aptly point out), should not be painted with the same brush. OTOH, retrofit zone control is usually a bad idea unless the duct system is being replaced.

I should also mention that zoned systems are often misused. The primary reason to zone is to achieve better temperature balance against dynamic loads (morning-to-afternoon, day-to-night, winter-to-summer). Of course, zoning can also be used to set different temperatures by zone. But savings can only happen to the extent that energy would otherwise be wasted overcooling or overheating part of the house to achieve comfort in another part.

It may be possible to reduce energy by turning down (or up) the stat in unoccupied rooms, but this can backfire. As we build homes tighter, wintertime humidity tends to be higher, which is a good thing to a point. But this increases condensation risk in unheated rooms.

Regarding separate systems for two-story homes: As I tried explaining in my previous comment, this option is becoming less viable as loads get smaller. And I’m not just talking about beyond-code homes.

BTW, I chuckled when I read your comment about using two sensors with one stat. I’ve been doing that in my own homes for 30 years (save one that had full blown zone control), ever since I beta-tested the first digital stats by Enerzone that supported remote sensors. Early on, I would install a switch to select which sensor was active. Today, different stats have different methods for selecting remote sensors.

David, I will stick with my
David, I will stick with my analogy that using dampers to control airflow is the same as using the brakes to control car speed. The situation that drives me crazy is when people put in a 5-ton, single capacity system with undersized ductwork and higher static pressures. There will always be at least one zone that does not get enough airflow. So what do they do? Put in a zoning system which results in dampers being closed on the zones with sufficient airflow so that more air can be supplied to the under served zone.

I will agree that damper-type zoning systems can work well with multi-capacity systems if the ductwork is sized properly and the control system is compatible with the heating/cooling equipment. Adding third-party zoning systems to variable-capacity compressor systems is not likely to work well.

For many cases, I prefer the approach where you have one system with two temperature sensors, one in the living area and one in the sleeping area, especially if there is only one bedroom being used for empty nesters like me. The control logic is such that the living area thermostat controls the system during the day and the sleeping area thermostat controls it at night. The “uncontrolled” zones just float, which is OK from a comfort perspective since they are unoccupied. This type of thermostat with multiple sensors is available, but not as widely as it should be. You can argue that this type of control may waste energy by over cooling or heating unused zones, but I still claim that it is better than controlling your speed with the brake pedal.

As for two-story homes, just put a separate system on each floor, especially when you have an open stairway, and do not ever set the upstairs thermostat on cooling when the downstairs thermostat is on heating mode.

@Roy, advising folks to avoid
@Roy, advising folks to avoid air zoning is a bit severe don’t you think? I share your sentiment re: misuse of larger unitary equipment. But it’s not always possible to apply multiple systems. So then what?

With homes verified to meet current energy codes, it’s not uncommon to see whole-house loads under 2-tons. As you know, it’s usually impossible to achieve good temperature balance with a single stat, especially in multi-level homes. In my world (beyond-code homes), load ratios greater than 1,500 ft2/ton are typical, and it’s not unusual to see ratios greater than 2,000 ft2/ton. That means I can (and often do) have zone loads too small even for a mini-split.

There’s no question that many air zoned systems are poorly designed, but your cruise-control analogy suggests air zoned systems are inherently bad, which is nonsense. We should be encouraging better training and design practice, not throwing the baby out with the bathwater!