multi-zone "standard" ac?

[Itsjustdirt]

Its time to toss our entire hvac system and start fresh. Everything is about 25 years old. Do they make reasonably priced ducted ac units that can cool/heat only one room at a time? We rarely have the need to heat/cool the whole house, but would like to run it every night in only a bedroom or two. Is this possible with a "standard" ac setup or do I need to go back to looking at mini-splits? We aren't a fan of the mini-split head look but love the idea of only cooling one area at a time. Thanks!

 

[WordMan]

We have a multi-zone system. You won't be able to get it down to individual rooms, but you can zone a couple rooms. We have 3 in a 1,700sqft house and love it. It also keeps the temps more even as you don't have to mess with the dampers so much.

 

[danski0224]

The "standard AC unit" isn't capable of reducing capacity to go along with reduced load (zoning). Standard AC unit that is zoned will need a "dump zone" and properly configured ductwork.

Multi-stage AC unit and variable speed (more like modulating) blower/furnace? Maybe. It will be a top end communicating system. Will require controls, dampers, good duct design and competent installation. Good luck.

Good multi-split units are not cheap and require proper piping/installation.

Not sure if any of the gee whiz high dollar stuff will ever pay for itself.

Maybe two or three much smaller conventional split systems. Probably not much more, or maybe less than the top end stuff and then there is redundancy. Outside space for condensers/power may be a consideration.

 

[WordMan]

The "standard AC unit" isn't capable of reducing capacity to go along with reduced load (zoning). Standard AC unit that is zoned will need a "dump zone" and properly configured ductwork.

Multi-stage AC unit and variable speed (more like modulating) blower/furnace? Maybe. It will be a top end communicating system. Will require controls, dampers, good duct design and competent installation. Good luck.

Good multi-split units are not cheap and require proper piping/installation.

Not sure if any of the gee whiz high dollar stuff will ever pay for itself.

Maybe two or three much smaller conventional split systems. Probably not much more, or maybe less than the top end stuff and then there is redundancy. Outside space for condensers/power may be a consideration.

Ours has a variable speed compressor and a variable speed blower.

As we were already buying a fairly "premium" unit, the expense of the associated pieces (control unit, dampers, etc) wasn't too much. I don't think it will necessarily "pay for itself," but it does allow for a more stable temperature throughout the house.

 

[Jackfre]

I know Fujitsu is now offering air handlers that can be used with their two, three and four ton units. I believe, but please confirm that the standard mini heads can be used with them as well. When you say, “toss” are you talking about the ductwork too? When I upgraded i ditched the entire duct system as well. I would suggest leak testing your current duct system to see if it is suitable to use with the newer equipment. In my home I have a multi for the 2nd floor bedrooms and a higher efficiency single for downstairs. We then re-modeled, adding space and one more high efficiency single. Redundancy is worth a lot in the AC world. The house runs comfortably and economically.

 

[yeldogt]

I lived in a big old 4 square w/ a large addition off the back ... The place had been seriously "upgraded" when the addition was installed in the late 50's. This upgrade included all new ductwork with proper supplies and returns --- part of this upgrade was to zone the house into three sections and add AC (rare back then) . Zones were all about the same load. 1st floor, 2nd floor and addition. The addition was to make the kitchen larger and add family room, bath and mudroom entrance. This was done by an old school oil dealer with own metal shop -- the system was a work of art. There was no multi speed equipment back then .... but, luck and skill with the layout allowed the system to work w/o a dump or bypass. The old dampers moved slowly --with zoning the goal is not to totally shut off an area ... it's to temper the space and not fight the extreme. Example: in the heat of the day --- why try and fight the heat on a second floor when no one is there? Allow the temp to increase and when the load drops at 6pm ... have the system drop the temp down. The same is true of the lower areas -- why heat in the winter ...allow them to get colder and only heat those where you are. When you want to bring the temps back the unit can hit the one zone for a short time with full capacity. This was a big house -- over 6k sf and even with the upgrades not as tight as something built today.

The problem with Zoning HVAC --- is finding someone. The vast majority of companies are clueless -- few have metal shops anymore -- most will not even do the simple math to understand what is even needed.

The sad thing is the new equipment makes zoning so easy .... The Carrier stuff I have been using for close to 20 years is amazing. In general the smallest zone has to be able to take 25% more CFM than the lowest CFM of the equipment. My new house has an odd bedroom that sits off to one side and is a bit lower than the surrounding building .... so cold air is going to drop to that area. Fine in the summer ---- not so good in the winter. I made that a bedroom area (has a sitting room and bath as well) a zone --- designed the ductwork to be able to take that 25% ... plus added returns to match a slightly higher CFM so in the summer if the cold air drops too much the return circulates the air out of the space. If the room/ zone coverage is a bit too small you can also add an extra supply to an odd area of the house that will always benefit from some extra flow -- you just add it to the zone trunk -- you don't change that areas factors. This just allows the excess to flow to a needed area and relieve the small zone . With new equipment - you don't do the old bypass dump (never a good idea IMO)

So you see -- doing it correctly is not just something that can be done w/o any math ..... It's a shame . There is a guy on the HVAC forum that will do a full load for a couple hundred bucks. Knowing the loads -- tells you the equipment size and the room by room load tells you what size ductwork you need. Almost always this results in smaller equipment with lower cost to buy and operate.

Every house is different -- so there is no one solution. In many cases the new modern equipment can fix old houses .... since most have small ductwork. Modern equipment "learns" the ductwork and with zoning can provide proper flow.

Mini-splits are great problem solvers ... they work well in new high efficient homes with more open floor plans. Not always the best when trying to do an older house with leaks and many rooms -- especially heat. I have used them mostly to boost AC in odd projects where ducted can't be installed or retrofitted.

 

[Syberia]

You can get mini splits with one or multiple ducted air handlers.

 

[Itsjustdirt]

You can get mini splits with one or multiple ducted air handlers.

Now this is an interesting idea. I wonder what the downside would be? Seems like a 3 zone system would be pretty easy with the ducted minisplits.

 

[Itsjustdirt]

You can get mini splits with one or multiple ducted air handlers.

Well, I just learned that the ducted mini splits must be installed in a conditioned space...ie: not an old house's attic. Darn.

 

[Firebrick43]

Why are you stuck on ducted systems? A minispit wall mount air handler is one reason for high seer ratings. The energy efficentcy drops off drastically if you use a ducted or kick panel unit instead.

Also Multi zone systems are nearly the same cost as buying two or three single zone systems and if one system goes out your not miserable as you would be with a multizone system.

 

[yeldogt]

Well, I just learned that the ducted mini splits must be installed in a conditioned space...ie: not an old house's attic. Darn.

While it is common to install systems in unconditioned spaces -- it's never a good idea. I'm surprised code still allows it frankly --- so wasteful.

Whoever told you "NO" or where you read it .... good source.

 

[yeldogt]

Now this is an interesting idea. I wonder what the downside would be? Seems like a 3 zone system would be pretty easy with the ducted minisplits.

Mini-splits are great problem solvers -- using them to heat and cool a whole house requires understating to what they can and can not do.

Multihead have a place and when done correctly work very well. At my beach house w/ hot water heat I removed a second floor split system in an attic and put in two ceiling units to do the two large bedrooms up there in the old part of of an extend cape. The space is two large bedrooms and a central bathroom. The old split died and the location in the attic poor. I also added a first floor 16x 22 extension at the same time -- installed a wall mini. All three run off a central compressor -- so I can zone each room. They will heat -- but -- the house has a boiler.

Minisplits can work very well in super insulated open floor plan houses for heat --- older homes not so much. AC is often as much about humidity removal as it is about getting the temp down -- so it's not as direct as heat is. A unit in one room can often work to cool another room next to it if there is enough air transfer. Trying to just cool one room -- while it is possible depening on size of the room. Doing so when the house has a split system makes little sence. The cost will never be recouped.

You should try and get some estimates for a VS system and see if you can zone it ...... this works for larger houses. In many cases just getting better newer equipment is the answer. If your old system is working well and provides quiet comfort throughout the house -- replacing is the best way to go .... don't overthink. New system can remove humidity and make no noise .... that's the goal

 

[Itsjustdirt]

Mini-splits are great problem solvers -- using them to heat and cool a whole house requires understating to what they can and can not do.

Multihead have a place and when done correctly work very well. At my beach house w/ hot water heat I removed a second floor split system in an attic and put in two ceiling units to do the two large bedrooms up there in the old part of of an extend cape. The space is two large bedrooms and a central bathroom. The old split died and the location in the attic poor. I also added a first floor 16x 22 extension at the same time -- installed a wall mini. All three run off a central compressor -- so I can zone each room. They will heat -- but -- the house has a boiler.

Minisplits can work very well in super insulated open floor plan houses for heat --- older homes not so much. AC is often as much as humidity removal as it is about getting the temp down -- so it's not as direct as heat is. A unit in one room can often work to cool another room next to it if there is enough air transfer. Trying to just cool one room -- while it is possible depening on size of the room. Doing so when the house has a split system makes little sence. The cost will never be recouped.

You should try and get some estimates for a VS system and see if you can zone it ...... this works for larger houses. In many cases just getting better newer equipment is the answer. If you old system is working well and provides quiet comfort throughout the house -- replacing is the best way to go .... don't overthink. New system can remove humidity and make no noise .... that's the goal

Thank you for your well thought out reply.

Our house is smaller, roughly 1100 sq ft. Basically, the living room needs heat or cooling from 7am to 9pm and two bedrooms need heating or cooling from 7pm to 6am. IE: something will always be on, but I dont thing running a whole home furnace/ac to heat/cool everything, all day/night is necessary. Our current system is ancient and is being trashed as a whole (ducts and all) as none are worth saving. We're basically starting from scratch which is exciting and I'm hoping I can get it right the first try. Most 3 zone mini splits are roughly 5-7k and a new hvac (gas) setup will cost about the same (talking materials only for both). With both being roughly the same cost, I'm leaning towards the mini splits

 

[yeldogt]

Thank you for your well thought out reply.

Our house is smaller, roughly 1100 sq ft. Basically, the living room needs heat or cooling from 7am to 9pm and two bedrooms need heating or cooling from 7pm to 6am. IE: something will always be on, but I dont thing running a whole home furnace/ac to heat/cool everything, all day/night is necessary. Our current system is ancient and is being trashed as a whole (ducts and all) as none are worth saving. We're basically starting from scratch which is exciting and I'm hoping I can get it right the first try. Most 3 zone mini splits are roughly 5-7k and a new hvac (gas) setup will cost about the same (talking materials only for both). With both being roughly the same cost, I'm leaning towards the mini splits

Making a tight house is what makes for comfort when heating in the winter .... with AC taking away the solar gain on the roof and having the correct size is important so it runs long.

My primary houses are in the midatlantic -- so we have hot humid periods and we have times when it's cold. So my systems have to work on both ends.

1100sf is not much to heat and cool ... it really depends on the layout .. and where it is. trying to heat in ME is not the same as what is needed in GA

 

[mikedodge]

There's going to be no savings by not heating or cooling certain parts day and night like that and will end up costing more in the long run having to install the more complicated system now and whenever it needs maintenance.

 

[yeldogt]

There's going to be no savings by not heating or cooling certain parts day and night like that and will end up costing more in the long run having to install the more complicated system now and whenever it needs maintenance.

No savings may be a bit too strong .... it really depends on the layout -- but, even my row in the city w/ three floors was over 1100sf. So I'm guessing not that 3 floor layout -- we did save something not maintaining full temp on all the levels. But -- you are correct it's not really for cost at that sf size

The zoning equipment is not all that expensive as an add on. The better carrier equipment (infinity control) is all set up for the zoning control board to be added (The main Thermostat is the same) The actual zone valves are not at all expensive. My last was about $1600 for all the extra equipment -- 3 zones and 5 valves.

Also -- I have never had any parts fail out of warranty. We lost a board on the first one we did at about 8 years in 2011 and I had an early damper start to make some noise on one installed about 6 years ago. No longer own the first -- sold it to a friend.

Most of the equipment is actually robust ..... Carrier has a 10 year parts warranty. Even if a board fails after -- at that point there is e-bay.

It's like my built-in refrigerator at one place. At about 10 years + or so you can pick up the $450 boards on e-bay for pennies. After a few years when they no longer make them they get expensive or impossible to get. I have spares of a few parts because I have to fix my unit as it's in the city and they no longer make that size. My plan is to paint the kitchen when I move ... not replace it for the want of a refrigerator.

 

[mikedodge]

No savings may be a bit too strong .... it really depends on the layout -- but, even my row in the city w/ three floors was over 1100sf. So I'm guessing not that 3 floor layout -- we did save something not maintaining full temp on all the levels. But -- you are correct it's not really for cost at that sf size

You're right multi level could have some savings especially if its not split level because some floors can can get more heat then others and more exposure etc. There's more potential for savings if it's a bigger house also. I was guessing it's a bungalow.

 

[65ranchero]

Have you looked into MS cassettes? wall or ceiling mounted
Below is just one example Google mini split cassette

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