zone systems on forced air furnaces.

BillW@honeywell

I agree that no amount of zoning will correct bad ductwork or wrong sized equipment. Forced air zoning has improved greatly since the early days, and many of the problems mentioned by Mike and Greg can be eliminated or minimized. We recommend installing a freeze sensor that prevents coil icing when only one small zone is calling. You can use a hallway or a basement or a return as a "dump zone" to relieve any static pressure problems. The key is to work with a contractor who is familiar with zoning and at least competent with ductwork, and most of the problems mentioned in the other posts won't happen. Most homes can be split into 2 or 3 zones. The only red flag I see here is the stud bay returns. It is very difficult to get good flow through them. If you are doing major renovation, abandon them, and run duct returns.

smoore

I don't have a lot of experience with duct design but a friend wanted me to look over some plans that a local supplier drew up for him. He is building a ranch home with a basement. This will be a rental, upstairs will be one unit and downstairs a second. they recommended to use one furnace and zone it with dampers in the duct(honeywell troll a temp). My concern is that in the basement they have seven six inch suppplys(770 cfm) and only two 2*4 stud spaces(300 cfm) for return air, the rest of return is taken from upstairs unit to complete return air needs. I thought that what ever you dump into a space you need to take out so if there only removeing 300 cfm there is only 300 cfm going in because of positive preassure? thanks for any help

Greg_4

You're on the right track-

You brought up a very good point to be considered. We have done a lot of forensic diagnostics on existing systems and so often we do not change out equipment, but instead alter, add, increase or otherwise correct ducting within offices, homes, etc. Also, often we may lose the sale because we've included work in the bid to correct IAQ, supply and/or return problems. This causes us typically to be higher in bid and the customer sometimes gets sold a bill of goods by being talked into swapping out their old HVAC equipment for new. Often, yes their utility bills may be lower due to efficiency improvement, but the old problems still exist - cold/hot or otherwise uncomfortable rooms. Think also what happens when the A-C condensor & coil for example, is sized to handle an entire home. By zoning the lower floor, basement or addition, how does the coil operate by being delivered the entire tonnage of cooling, when only a few hundred cfm is being pushed through it? TX valves will help (we almost always intall them), but we have seen a system fail, freeze up, etc. due to these types of circumstances. If designed properly, zoning can work wonders, but additional cfm's may need to be 'dumped' into another area to help a zone system work. Properly sizing equipment and ducting - both return and supply is so critical in any system. Greg

Mike T., Swampeast MO

Zoning Air

Many schemes have been done over the decades and the newest always claims to solve the problems of the previous...

Zoned air systems only make a bad situation (pressurization imbalances) worse. Couple that with the wildly varying requirements of a ranch home basement/main floor & heating/cooling season and you're inviting problems.

For TRUE zoning, hydronics absolutely rule.

If that person expects he and his renters to both be reasonably comfortable, he had best install two separate systems or use hydronics.

If there were a reasonably priced, reliable and comfortable forced air solution to this, it would have been perfected LONG ago!

Dave Flood

Hopefully you'll still be friends at the end of the job. Zonig can be a tough call sometimes, and there are trade offs. It sounds like your installing 2 tons of ac downstairs based on the 770 CFM you spek of. What is going upstairs, and what is your total load. When one zone closes, we rely on the second zone to handle the whole load. The second zone normally can't handle the whole load, so we install a dump damper to relive static pressure. Problem here is, the are that gets dumped into is either a sauna in the winter or a meat locker in the summer. Many contrators feel its is a waste of energy to dump the load in a small application as a ranch house and run the whole house as one zone. Not everyone agrres with that. The recomended static pressure in a residentail application is .10 friction setting. When istalling a zone system that static pressure increases. As I recall, Troll-A-Temp use to go up to .35. When your staitc pressure goes up, you'll have a higher velocity of air which you will hear. I recomend you higher a reputable HVAC Contracotr to design the duct system for you.

Dave Flood
Dir of Tech Ed
ICPA Tech Trng Ctr
Wallingford, Ct

don_9

Well for not doing much duct its sure sounds like you done your homework. For sure that room will have a positive pressure,You can only get back what you put in.Its like closing a door or a vent then wondering why you have comfort problem.

Asked this guy to show you what external static pressure(esp)he started with .then is pressure losses,then what
available static pressure was left.If he unable to answer
and show you on paper these few simple question then I would
advise you to find someone who know's proper duct design and have it done right.

I am with Mr honeywell,The proper duct design match to a vav zone damper system You will have great comfort level with no jet noise.If it walk like a duck and,ahh never mind.
Good luck

Mike T., Swampeast MO

It's the return flow

that seems to cause problems. It's not too bad in heat only systems, but supply & return issues in heat/AC systems aren't too easy to deal with. I've helped a number of cold, drafty rooms in otherwise tight homes with reasonable ductwork not by trying to increase supply, but by putting magnetic covers over a significant portion of the affected return grill(s).

A couple years ago we had a very unusual (unique in even old peoples' lives) long period of constant below freezing weather where snow did not melt for at least 2 months. I noticed something strange on quite a few new homes--snow & ice remaining on roofs only directly above rafters. I know the interior of some of these and believe the problem was excess pressurization forcing warm air into the attic through recessed lighting. I wasn't able to verify this, but I suspect that warm humidified air was condensing on the coldest thing in the attic--the rafters.

In the uncommon forced air system where returns are balanced to the supplies of each space (and not using bare joist/wall cavities) it seems to me that zoning will throw the entire balance out of whack as all the zoning systems I've seen only address the supply. I suspect that if the return were zoned as well, that the cost would exceed that of separate systems.

These supply/return imbalances simply can't occur in a hydronic system. Only when hydronic systems are micro-zoned (way beyond the ability of zoned forced air systems) do problems occur. Buffering--similar to "zone dumping" BUT not so wasteful as with air--and/or proportional control can readily solve this problem.

I'm not saying zoned air systems won't work--particularly with 2 maybe 3 zones and a good duct system, but with different families in the main floor/basement of a ranch home? for both heat and A/C?

Earthfire

rental zoning

In rental housing each unit Should have its own dedicated water meter, electric service and heating system. In most states the landlord must pay for utilities if not dedicated to unit under sole control of tenant. Especially with a air duct system will tenant 2 want to deal with tenant 1's passion for cabbage and beans cooking in the apartment, or the sound of tenant 1's bedroom calistencsas they echo thru the ducts. Tenant turnover is an expensive headache that can be mitigated be a little forethought and planning during the construction of the building