HVAC Zoning: Do You Need It, or Not?

We get asked this a lot, so here we're trying to explain as concisely as possible why zoning is often a symptom of a badly built home enclosure (or a poorly planned McMansion, obviously). If heat is bleeding through the skin of a home at a controlled rate in every room, there's no need to zone the HVAC system to give special attention to a weak link. There are no weak links in a well-tuned home enclosure, and so your HVAC system can be simpler with fewer components, and more sure to effectively condition the home.

[timdestasiohvac]

Ok Corbett, here we go:
1. Agree that zoning done wrong has given zoning a bad name. We have successfully used zoning on existing 2 story homes with 1 system, 1 thermostat and given both floors comfort by adding zoning and a second thermostat. Yes, we didn’t address the home performance problems, but we weren’t called for that and we were working within a budget.
2. Every and I mean every multi level high performance home that I have ever done has been zoned. One main reason is that the loads per floor, or per zone, are smaller than the smallest tonnage of conventional HVAC equipment and I didn’t want to oversize.
3. Zoning prevents over sizing. Especially if you run simulations where you diversify the load. For example, if we have a total block load of 4 tons, and the home is divided into 4 zones, we usually put in a 3 ton system because not all the areas in the home are at peak load at the same time. We can move that 3 tons around to follow the sun or occupant load.
4. Zoning is code compliant. In NC we are not allowed to use a single system for multiple floors unless it is zoned, high performance home or not, the code doesn’t care. The only other option is each floor gets its own unit and that gets expensive.
5. Zoning keeps the budget down. Initial cost and total cost of ownership. I would argue energy bills would be lower compared with multiple separated systems, as long as multi stage or variable speed is used in zoning.

Now with all that said, if you are going to zone, you gotta do it right. You must use multi stage equipment or variable speed/ communicating systems. Never ever use a bypass. Size ducts and divide zones evenly so that a worse case scenario doesn’t try to force too much air through too small ductwork. Set up the zone controller so that it doesn’t kick into high stage with only one zone calling. Put returns in open areas, never in small rooms to avoid pressure issues when that zone isn’t calling. When done properly, I really think a zoned system is better than 2 units. Commercial buildings have been using zoning for decades. They do it right. With variable volume blowers controlled off supple static, multiple stage cooling, controlled off supply temperature, and each zone had a Variable Air Volume box with a damper and sometimes a blower. There is no reason why a resi zoned system can’t work well too.

Thought? 🍻

[compactc]

My want for zoning comes more from a point of wanting different temperatures in these zones. I realize that in a properly built home, keeping one even and consistent temperature does NOT require zoning, but I'm not sure how else I could keep, say, different bedrooms at different temperatures. For example, MY master bedroom will end up with the thermostat set at somewhere around 63-64 at night, because I love it COLD. Anyone else in the house will inevitably complain that "its too cold, can't you turn the thermostat And the answer will be a loud NO

[kylemacht]

In my experience, you still can get temperature and humidity stratification between floors of a high-performance home. This is why we typically mechanically separate floors and remote spaces. Typically we doing this with separate air handlers with VRF or variable speed units on a hydronic distribution system.

[shawnriley]

@Home Performance We do install zoning under certain circumstances. We won't install zoning with a single stage system--it has to be a minimum 2-stage compressor or (preferably) variable speed. Since Manual J & D are used in design, not many of our design houses are zoned unless they meet our criteria. For example, if a homeowner wants one room (like a master bedroom or a FROG) to be cooler or warmer than the rest of the area, or if they have a relatively small FROG, we will usually use a Mitsubishi ductless or ducted unit for that area. You are correct, zoning can definitely cause more problems than it fixes, if not done correctly.

[jeffm]

We are currently building a new house in east Texas and have decided on a zoned heat pump. My 88 year old dad has moved in with us and it's impossible to keep the temperature where we are all comfortable. So we have 3 zones, living/dining/study on 1, master bed/bath on 2, guest beds and bath on 3. There is an additional small outlet/inlet running off zone 2 into our fully conditioned attic.

[ericlebarron]

I can't find which publication mentioned it for the NIST's NZERTF house in Maryland, but the researchers found something like a 6-degree difference between the first and second floor. The conclusion of the paper suggested testing if a ceiling fan over the stairs could help mix and reduce that stratification.

[brettzeigerbacher]

I take it thought that the control for the vent hood operation and how that interacts with the rest of the house ventilation (via the exhaust damper / increased intake) is not considered zoning in this definition.

[cellocovers]

What if you have a home where certain rooms you only use when you have guest periodically? You could have a a ductless minisplit, which would be ideal, but if you already have a central hvac system, then maybe zoning is a good way to deal with what you already have cost effectively. If you are planning a completely new hvac system for a new construction home, then zoning doesn't seem like a good idea.
TLDR IMO zoning is a good way to deal with an existing hvac system where you don't use certain rooms for much of the year.

[KPHVAC]

I agree that zoning is NOT necessary for most new construction homes that are high performance. Get your HVAC contractor involved in the planning phase of a build. If you want a comfortable home the HVAC system WILL require space and a good design. Also, a high performance system will be a larger investment up front. All metal ductwork that is custom made, sealed, and insulated, is going to take way more time to design and install.

For large multi story homes a zoned system or going with 2 or 3 separate systems may be a good solution.

[beurky]

Zoning, meh

Multiple systems, much better.

Small footprint with high height, or otherwise 4 floors. Stack effect really comes into play here. Air sealing helps, but I find it doesn't solve the issue of temp fluctuations from floor to floor.

Especially in zone 5 or 6 where you have good winters and summers.

My Future building goals are one system per floor for independent control.

[gregoryschondelmeier]

Hi @homeperformance.. we've gut-reno'd our house in NY (40 miles north of NYC) and added a 2nd floor. We're moving away from oil and installing ducted heat pumps. I'd asked the 2 HVAC companies to price out 1 zone downstairs and 2 zones upstairs (2nd floor is two sides, primary suite and 2 kids rooms, with vaulted ceiling above stairs). One company said you shouldn't do it, the other has it in the bid. We'd have a stacked Mitsubishi 48K unite outside with 1 30K handler in basement and 1 24K in attic. The 24K would be split with zone dampers. We'll have all new spray foam and Anderson 400s. Is this overkill? I dont' want to jeopardize efficiency of 2nd floor unit by modifying to be 2 zones. We need to make a decision soon to stay on schedule! Many thanks.

[BittyVids]

My house has a mother in law suite addition. I’m adding a ground source heat pump. She likes extra heat and less a/c than the rest of the house. Would a zone system be better than installing two separate heat pumps?

[ThePositron]

Interesting to hear this. My builder and a few HVAC people have also told me they don't recommend zones, but I thought they were just trying to cut costs. :)

I am very interested in zones for two reasons.

1. It seems worth it to me to have the master on a zone so I can be cool at night and the 3500 sq ft rest of the house doesn't have to spend the energy to stay that cool. Is the ROI not there?

2. We will have a media/exercise room that will be empty for long stretches, then suddenly have many people or one sweating person. The media room will also have interior insulated walls and hopefully a somewhat tight fitting door. I'm worried a tiny miscalculation in the Manual J will mean it's too hot or cold. And also.... same question about ROI. If it's regularly unoccupied for 72 hours we could keep the door closed and the temp at 80.

[davetaylor]

Corbin, my complements on a very direct and well spoken video. Keep up the good work educating the masses.

[Atlantisxx]

In a modern home you want zoning combined with a control system ex. Knx, to tune temperatures based on occupancy.

[stringsandapick]

Tested a house last week with a zoning system. The ductwork (return in particular) had holes I could stick my arm in up to my elbow. No way this system would work effectively. 2nd floor return vents couldn't even turn the anemometer.

[johnwhite]

Corbin-?important to note dampers zoning are 1) additional design burden )2 additional expense 3) additional thing to go wrong(can u access the damper?) that said I think your perspective also assumes open floor plans and always on ceiling fans - you have fans in EVERY. Room right? So I think a competent designer/installer can easily justify a two zone system in two story situation we here spaces equal volume and different facedas glazing e.g enclosed basement first floor with (35per cent glazing

[TeresaAvery-sz]

What about a barndominium? We have a 32' wide great room with 20' ceilings, separating the master suite from the guest bedrooms. We will have radiant heat in the floor and closed cell foam top to bottom. We are building in Virginia.

[turboflush]

In my area and experience; no one here can even fathom a high performance setup. Manual j in 1 min before they leave the house and toss in a unit that in the past has worked for others.
Very frustrating.

[josephmerritt]

Great discussion. IMHO to convince people, you need to have a good discussion about comfort, and if that is successful then transition to how to make it happen with a high-performance home with HVAC/ERV. Most homes in the US are not high-performance so to achieve what people sense as comfort they are applying bandaids because of improper insulation, lack of an air barrier, incorrect window sizing coupled with improper windows, poor humidity control, and erratic ventilation among other issues. Robert Bean Retired ASHRAE & Distinguished Lecturer (Linkedin) may be helpful in planning the comfort discussion.