I have several questions regarding heating system planning in general and one project in particular,so I think I will break things down into different threads,rather than have an all over the place discussion.

I am new here and am not certain that this is the correct forum,as this subject is not really a strictly radiant related matter,and I am not interested in strictly radiant systems,but the discussions here seem lively and helpful.

So,I would like to start a discussion about zoning and microzoning(not really sure what the specific differences are).I would have to believe that this subject would have to be near top as it relates to system planning,as it would have to have a large effect on equipment selection.It seems that home builders in the past just wanted to deliver a pretty much homogenous condition in the home,heating and temp wise.Then,starting in the early 90s or so it seemed that multiple zones,circulators and valves became common,some times,the more zones the better mentality prevailed.Now it seems that some at least are giving zoning more thought.

So,my first questions is,where does it make sense to create separate heat zoning?Especially given that houses and floor plans are more open than ever,and that living areas are rarely compartmentalized anymore.Even floor to floor separation is limited.So,where to start?

In my opinion, if the heating is in a concrete slab or gypcrete, it should be one zone (one t-stat), typically one zone per floor (assuming you are not building a ranch). The exceptions to this are if different areas of the house have quite different heating needs, sunroom vs basement, for example.

Lots of people put in 10 or more zones and all that does is make for a more complicated and costly install. Balancing and tube spacing can do much of what a t-stat can do in terms of higher or lower average temp in the room. Most people totally forget about the t-stats after they move in so I would rather put the extra money into solar or a better boiler. Just my $.02

If the people forget about the thermostats, then the thermostats are doing their job. the point of a thermostat is not for people to change them all the time, the point is so they can set the temp they want in an area and get it.

there are people who are happy with single zone flow balanced systems. but they are not that common in my experience. Some people are better served with more thermostats and some are not.

the reasons to add a zone are numerous:

1. Different water temperature requirements for different spaces may make temperature range undesirable between them (carpet flooring, different install types)
2. Different occupants of different rooms may desire different temperatures (sally likes a cold bedroom and grandma likes it hot)
3. Activity levels in different rooms may dictate different temperatures (exercise areas, bathrooms)
4. An area may have a large heat gain that doesn't reach other areas of the home well (fireplaces, woodstoves)
5. Solar gain differentials for cooling systems
6. Different mass of the emitters may change heating/cool down time and make performance unnacceptable (slab bumpout with joist radiant main floor, etc)
7. Different areas may want different schedules for occupancy/setback purposes.

As long as everyone wants a CONSISTENT temperature, flow balancing can achieve a bit, and in some install types choices like plates or tubing density can do more. But then you are trading design complexity for equipment complexity and you are gambling that the occupants will be satisfied with a lower level of control. Simple houses can of course get simpler systems... a slab on grade with a couple bedrooms and a main area can probably be designed to run on one zone pretty well. a 6,000 sq ft two story house with basement and 4 baths... no.

the cons for adding zones include:

A. increased heat source cycling, which may necessitate changes in your firing settings, adding mass in a buffer tank, or more capable controls that can organize zone firing to reduce cycling.
B. install cost and complexity increases... actual cost and complexity issues depend on the installer, of course.
C. more zones is more work to turn system up and down if you leave for weekends or what have you, and may necessitate an upgrade to allow for networked or "one button" setback control.


in air systems microzoning is not even an option unless you're doing chilled water hydroair systems. then the trick is finding fan equipment set up properly for small zones!

Thanks for that Mike and Rob.My next question is then...when is zoning practical and effective?It would seem that zoning would be much more effective,obviously,in a large home of 6000 square feet,because distance alone could keep different areas thermally isolated.However,as you mentioned above,what about Grandmas and Sally's bedrooms?If they are adjacent rooms and grandma likes 74° and Sally likes 60°,how practical is that? Can it be accomplished on a radiant slab? I could see it with hydronic baseboard,if you were to create 2 distinct thermal envelopes.But at what point does zoning become pointless? And can it become even counter productive,if the desired temperature differences are too large and 2 areas are not thermally isolated enough?

if you insulate between zones you can do pretty much anything you like. A 15 degree differential is pretty extreme though, and it all depends on heat gain to a space and it's heat loss to the outside. If sally's room is 15 degrees colder, it will tend to pick up heat from the surrounding zones. If it's surrounded on 3 sides by 15 degree warmer zones and not insulated in the slab or walls between the zones, especially if she's got a low heat loss, then sally's room may not stay 15 degrees colder.

if you want sally's room colder most of the time but you want to be able to heat it up more when cousin jake comes to visit and sally sleeps on the couch, then you definitely want a zone.

If you want extreme temperature differentials you want insulation between zones, again, unless the thermal bleed isn't that significant or heat loads are very high. For example, If you want your great room 15 degrees colder than an adjacent bedroom, it's generally unlikely bleed from the bedroom will elevate the great room temp because it's load is so much higher.

Rob,if we are talking separate zones on the same slab,are you suggesting a thermal break in the slab?And at what anticipated temperature differential would this apply?

And here is another zoning example question.If you were to have a single family home,2 floors,with a generous open stairwell between levels,is there a point where trying to maintain a temperature differential is counterproductive from an energy use standpoint?For example,on a cold winter day,daylight hours,trying to maintain 72° on the lower level living area(where all the occupants are) and 55° on the upper level (no activity).In other words,the lower level heating now takes on additional load imposed by the upper level.

you cant quantify this for all conditions with a simple answer, but if you only want a couple of degrees difference you don't need to worry about this much. if you want 15 degree DT, then you want thermal breaks in slab/walls in most cases. at least, if you're heating with slab radiant. forced air probably won't transmit that much energy through the slab. this is really a case by case analysis if you have specific needs and questions. border area, temperature difference, heat load and heating method all play a part.

no problem turning down upper floors. being doing it for centuries to good effect. only question is how cold are you willing to allow the second floor to get, and at SOME point in SOME homes you may find a max differential where you outstrip the 1st floor heating emitter's capability to deliver heat if it's meeting a higher than designed load... probably only an issue on the coldest days of the year and in very extreme differentials.

in some cases, if the 2nd floor load is very low and barrier between 1st and 2nd also very low, and if you are happy with a 5+ degree differential, you might not even need 2nd floor heat.

So,is the bottom line with regards to 1st floor to 2nd floor differential,if you are maintaining the desired comfort level on the occupied 1st floor,you will always have energy savings,no matter how low you have the Tstat set to on the upper floor?

it is unlikely that you would discover a situation where that is not true. however, possibly, if you were in a situation like this:

Say you are using a very temperature or output sensitive heat source, like a heat pump. IF this extra load triggers electric resistance backup heat, you could shoot yourself in the foot.

It is interesting in that we (north american heating designers) tend to plan so that the home owner has a great degree of control over the heating system. But as Rob and I have both noted, there are drawbacks, complexity/cost being the biggest one. We (my company) are going even more down the opposite path which is having the system run only on outdoor sensor and a control that takes care of floor heat/HRV/DHW and cooling all in one. No indoor t-stats. It is a different philosophy. Some people like it and some can't handle not having control. It started from our commercial work where one person would turn a t-stat up and another down and nothing worked right.

BTW, floor heat is very resilient and you can have equal comfort with temps up or down a couple of deg. I have never seen a system where HE and SHE both like the same temp as much as radiant.

Hey Mike I like your point.When in doubt I always side with the simplest way.All the gadgets get a lot of enthusiasm in the planning stages,but then get quickly forgotten.Unless one of those gadgets screws up.And the more fiddling they invite and the more hands and minds messing with equipment.And call backs and so on and so forth.

I would say that in today's world comfort is comfort,either you are comfortable or you are not.So,how to achieve that in the most simple way?

To me zoning planning would lean much toward the energy savings part of the equation.

And I like the feedback about living with radiant comfort and the experience.I have never lived in a house that had any radiant.

"I have never lived in a house that had any radiant."

Now that, is sad.

Yup,and pretty lame,too,I might add.

The more attention you pay to proper insulation and air sealing, the less zoning and "microzoning" issues are going to arise.

I'm just pushing warm water through my entire system right now without any control at all and it's working pretty darn well. The zones are there and wired, but I haven't turned on the controller. I don't even have any heat on my entire upper floor and it's still fine from the main floor warming. It's been in the 30's today with winds of 20 knots gusting to 30 and inside it is 65-68.

Common sense design plays a big part, too. For example, if you want to put some giant windows on the North side of your house, you are more likely to need zoning in those areas.

systems have been run on outdoor reset only for a long time. Viessmann, buderus, and many european systems have been run that way for years, in fact the daikin that ICFhybrid and I have comes set up to run constant circ on outdoor reset only out of the box.

however, even the euros have ended up adding analog flow control valves to most of their systems (TRVs, etc). because MOST people are not happy with that level of non-control. and on the whole we do not build houses that work well with that strategy very often here in the US. You can, but it requires a whole building design approach.

Rob,that will probably change over time.People are conditioned to tinker with the thermostat here,as in "make sure you turn the heat down before bed,make sure you turn the heat down before you leave,etc."Even the folks who were so insistent about having the setback thermostats,slmetimes 7 or 8 in a house,end up with them on manual overide. But I see more change in the last 5 years than in the previous 50 and as people get accustomed to it and systems operate correctly they will just forget about it.

in the radiant world we fought that battle for about twenty years (collectively). I would not hold my breath. especially since, again, most homes in america are not built to make that control method easy or particularly effective.

Radiant owners =control freaks???

Radiant owners =control freaks???

I wouldn't say that, though most people who get radiant care about comfort more than others. I'd say it's very, very limiting to have no control whatsoever over your internal temperature or to have it only in an indirect fashion for the entire building. UNLESS YOUR HOME IS BUILT FOR THAT TO WORK WELL, it doesn't. you have warm spots and cold spots and it takes a lot of design, or fiddling, to balance it all out, and then you have to be happy with either no adjustment or adjustment buildingwide only.

that simply is not a control profile that works for american homes. in most cases. if comfort and efficiency are actually important to the occupant. it's simple, yes. and that's all you can say in its favor. it's even simpler to put electric baseboard in, but that's not a great choice for most people, because simplicity isn't everything!