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Below are questions that we asked ourselves, and conclusions that we arrived at over the course of developing our Green Envelope
QUESTIONS AND ANSWERS
ENVELOPE
How can you produce a luxury house that is green? Isn't that a contradiction in terms?
Our goal was to minimize the energy needed to achieve the desired level of comfort. If the owner prefers to keep
the thermostat set to 80 degrees, our house will use less energy to keep it at 80 than one that is less green.
But you can't have your cake and eat it too, can you?
Fortunately for everyone, there is some natural synergy between comfort and efficiency. For
example, if there are no cold drafts in the house, it is more comfortable and you use less energy.
But there is a limit, right?
Our goal was to build a house that would use as little energy as possible no matter how extravagent
the usage.
What is the starting point of building an efficient house?
The envelope. A super-tight, super insulated house is easier to heat and cool. No matter what your fuel
choices, the first step is to reduce the amount of fuel you need.
What do you mean by super-tight and super-insulated.
We used spray foam insulation in the entire outside shell of the house, from the rim joists
through the attic rafters. Foam seals up every hole and prevents cold or hot air from getting
in and prevents circulation within the insulation cavity from transferring heat.
Why not use fiberglass?
Fiberglass is a mediocre insulator but it is very cheap so it is widely used, especially by
builders who are not going to recoup the energy costs via lower fuel bills. Fiberglass does not
seal tightly and the air that moves through it carries heat in and out of the house. Additionally,
fiberglass is nasty to work with and the glass fibers that get into the air are known health risks.
There is no fiberglass in this house except perhaps the insulation in the sides of the kitchen range
where high temperatures make glass the best choice for an insulator.
Why does foam do a better job of sealing the walls than fiberglass.
There is no comparison. Even when it is installed correctly, which is rare, fiberglass allows
air to flow through it and through the numerous punctures that the building process put into it
(nails, screws, electrical boxes, wires, pipes, etc.). Foam seals around all penetrations, wires
and pipes.
What kind of foam did you use?
Icynene spray foam is a soft, open-cell flexible spray foam.
Why not use hard-cell foam?
Hard cell foam is a slightly better insulator per inch which means you can use 20% less of
it to acheive the same R value. But our 6" walls and 12" rafters are thick enough that we have plenty
of room for enough of the open cell foam. Additional R value would not result any significant savings.
Is hard-cell foam better because it is more rigid?
Some engineers like hard-cell better because it is more rigid. Others prefer soft-cell because it
is less rigid. We are in the "flexible-is-better" camp. We hope this house will last decades or
centuries, and we think a more flexible foam will better withstand the inevitable small
movements and flexing of a house through the decades.
Is hard-cell foam better because it is a better vapor barrier?
Some builders think hard-cell is better because it does not allow water to get through. No one wants
water getting into the house, and no one plans to have the roof leak. But if some moisture gets through
the roof, we'd rather have open cell insulation to allow it to dry. If there is a big leak, we'd rather
have the water come through the insulation so that we know where the leak is rather than having it
trapped above the insulation and rotting out the roof or running to another part of the house. So
we prefer open cell for the same reasons some people prefer closed cell.
If the house is so well sealed, what about fresh air?
In a well sealed house, it is necessary to supply fresh air.
Doesn't supplying fresh air defeat the purpose of insulating?
We use a heat recovery ventilator to extract heat from the air leaving the house and transfer it to the air entering
the ventillation system and vice versa in the summer.
What do you mean by a heating and cooling delivery system?
A boiler burns fuel to heat water or air which needs to be delivered to the rooms in your house.
Likewise, air conditioning equipment uses electricity to cool air which then needs to be delivered
to the rooms in your house. While you may replace a boiler or a/c compressor every fifteen years, the
delivery system for the heating and cooling is in your walls for the life of the house. By
choosing a maximally efficient delivery system, your house will not only be as efficient as it can
using today's boiler or a/c unit, but it will continue to be maximally efficient with tomorrows better
technology.
But isn't a delivery system just ducts?
In this case, we chose to use radiant tubes to heat the entire house. Hydronics is fundamentally more
efficient than air in delivering heat across distance, and radiant heat is almost universally regarded as
more comfortable than forced air. However, except in dry desert areas, a conventional air conditioning system
works better because it makes it easy to remove moisture from the are. So in this case, it is "just ducts". But
in this case, the duct work is done right.
Why is it better to have separate a/c ducts?
Even if we were doing forced air, we would want to do a separate a/c system rather than combining heat and cold
ductwork. The optimal positioning and sizing of duct work for heating is different from the optimal duct work for
cooling. For example, it is better to supply hot air from the floor since hot air rises. But for the same reason
it is better to supply cooling from the ceiling. Additionally, properly sized a/c ducts are much bigger than they
should be for scorched air. Systems that try to do both must make heavy compromises in both comfort and efficiency.
Why seal the a/c ducts?
Event though the ducts go through conditioned space, we installed them using ACCA recommendations including sealing them
very tightly. This took a lot of work but it means that we are delivering cool air where we want it, not into the wall
cavities.
How is radiant heat more comfortable?
No drafts. Less dust. Heat is where you need it. In a room heated with radiant heat, the temperature at the
floor is very close to the temperature higher up. In a room heated with scorched air, the temperature at the
ceiling is considerably higher than the temperature at the floor. This is the opposite of what you want from
a comfort standpoint. People are more comfortable when their feet are warm, and even tend to prefer a lower
room temperature if their feet are warm.
Will the radiant floors be warm?
Because the house is so well insulated, it would overheat if the floors were kept so warm that they would feel very warm.
But they will feel somewhat warm or at least they won't feel cold.
If radiant heat is so great, why not radiant cooling?
We think radiant cooling has great potential. But in a somewhat humid summer climate, you need to control humidity
in the air as well as temperature which is most efficiently done with a conventional a/c system.
Why does the temperature of the water in the radiant tubes matter?
The lower the water temperature in the heating system, the more efficient. A well designed delivery system allows
lower temperature water to be used since it does a better job of transferring the heat from the water to the room.
Why not geothermal?
Geothermal heat pumps use electricity to transfer heat between tubes buried outside and the house. In this area,
electricity costs make the payback on a geothermal system slow, and the small lots make it expensive to install.
However, if the costs change or technology improves, the current delivery system would be perfect for a heat pump.
What kind of windows were used?
Marvin windows with a high energy rating were used. Additionally, advanced installation techniques minimized the
heat loss and gain around the windows. (link to pdf). It takes longer to install windows this way which is a shame
because it means that most builders don't bother. But again, we don't mind spending extra time to do it right.
What is the expected heat loss for the house?
basement bath 515
finished 6430
mechanical 3169
winecellar 837
basement Total 10950
first dining 2643
eating 2799
family 1934
fronthall 420
kitchen 2176
living 3232
mudroom 1760
powderroom 398
sidehall 5
study 3404
vestibule 1326
first Total 20098
second br2 2238
br3 2616
br4 2127
frontbath 915
hall 18
masterbath 1177
mastercloset 1212
mbr 6451
sidebath 639
second Total 17392
third attic 0
br5 2686
rec 3430
stairwell 1191
topbath 1553
third Total 8860
Grand Total 57300
What is the expected heat gain for the house?
Floor Room Sensible/Latent/Total
basement bath 43/48/91
finished 1582/767/2349
mechanical 583/617/1200
winecellar 94/115/209
basement Total 2302/1547/3849
first dining 1668/244/1911
eating 1506/410/1916
family 1089/240/1329
fronthall 92/117/209
kitchen 4327/334/4661
living 2039/294/2333
mudroom 848/206/1053
powderroom 191/29/220
sidehall 1/1/2
study 1571/579/2150
vestibule 1007/105/1112
first Total 14339/2558/16897
second br2/1628/403 2030
br3/1912/433 2345
br4/1153/240 1393
frontbath 462/77/539
hall 4/5/9
masterbath 557/124/680
mastercloset 475/111/586
mbr 4508/1205/5713
sidebath 274/61/335
second Total 10973/2657/13631
third attic 8300/2600/10900
br5/1237/413 1651
rec 1421/320/1740
stairwell 622/3/625
topbath 572/160/732
third Total 12152/3496/15648
Grand Total 39767/10258/50025
Why were no radiant tubes run in outside walls?
All the heating was kept inside the building envelope. The tubes were insulated even though they were
all in inside walls in order to better direct the flow of heat to where it was needed.
Where was the a/c ductwork installed
The a/c duct work was installed within the conditioned space. This resulted in a much more efficient system.
In most cases this meant the ductwork ran in inside walls. Even on the third floor where the ducts had to be
in the rafters in order to cool from above, there was insulation between the ductwork and the cieling thanks
to the 2x12 rafters.
RADIANT
Why use radiant at all?
More comfort, more efficient.
Why use radiant under wood (why not just mud jobs)?
Wood is an insulator so from a heating efficiency standpoint, it is not the best radiant floor surface.
However, we love wood floors and chose tose them anyway. By install a maximally efficient radiant sandwich
under the floors, we bring the heat as close to the finish surface as possible.
Will the floors be hot?
No, but they won't be cold.
Will the heat be even?
The heat loss of the rooms is highest near doors and exterior walls, so we put more tubing near the outside
walls. The result is that the room temperature is even. However, the floors near the outside walls will be
warmer than the floors near the inside walls. If you have pets, you might notice them napping on the warm parts
of the floors.
Why were tubes put in the basement walls instead of in the slab?
A basement slab is a natural place to put tubing since it is relatively easy to install. We wanted to keep 7'
basement ceilings so we only had enough room for 1" of XPS insulation under the slab. The water table was also
rather high in this neighborhood so the ground below the slab will be damp. Accordingly, we were worried
that there would be too much heat loss below the slab. So we put radiant tubes in the plaster walls in the basement.
These heat just as well as they would in the slab but were more expensive to install since the walls could
otherwise have just been done with sheet rock.
Why not solar?
The tight building envelope and efficient heat delivery system make it a perfect candidate for todays and tomorrows
solar technology. The cost of the equipment was the only reason we did not install solar panels on the roof now. The
payback is currently too slow, but we expect this to improve with time. In the meantime, the house is ready to
take advantage of future improvements.
RADIANT SANDWICH
Why not staple up?
In a "staple-up" radiant tubing delivery system, tubing is placed beneath the sub-floor. This is an inexpensive way to
install tubing. Typically the water temperature must be considerably hotter since the heat has farther to go before
reaching the room. We consider staple up to be much superior to forced air, but it is not the optimal way to install
radiant heat.
Do "mud jobs" work well for radiant floors?
Concrete (or gypcrete) below tile is the most popular floor surface for radiant heat. It is relatively inexpensive
and easy to install radiant tubes in the "mud", and the resulting surface transfers heat well, allowing the use of
very low water temperatures. Such floors store heat well too which is an advantage if the heat goes off, but it
means that they are not responsive in that it takes a long time for them to heat up or cool down.
Why not use mud jobs everywhere?
We like tile floors for bathrooms and entryways, but we like wood for most other rooms even though it is less
efficient with radiant heat.
Can carpet be used with radiant floors?
Carpet is an insulating material so it works against radiant heat. We recommend that throw rugs be used instead of
wall to wall carpet so that you still get good heat from the outside edges of the room where you most need it.
Why not use roth panels or quiktrak?
Roth plates and Quiktrak are pre-fabricated panels that are made with plywood, insulation and aluminum and either replace
the subfloor or sit on the subfloor directly below wood flooring. These are excellent radiant solutions and easy to
install. We prefer our sandwich, however, because it allows us to use more and better insulation and better aluminum
plates to bring more heat closer to the finished floor surface.
Why not use a router on plywood?
Routing groove into plywood in the subfloor is a good way to do radiant. We like our method better, though, since we
end up with XPS next to the tubes which is a better insulator than plywood.
Why all the XPS?
We insulate three sides of the tubes so that all heat is directed up.
Why all the intricate jigsaw work on the grid/sleepers?
In order to match the strength and stability of routed plywood, we cust elaborate meshes out of the plywood so that the
pieces retain stability with plenty of room to nail the hardwood.
Why not make the sleepers wider or narrower?
We made the foam as wide as we could while still leaving 5 inches of plywood to hold 2 nails.
Why use the Embassy plates?
These are nice beefy plates which transfer heat nicely. They are more expensive than alternatives, but the allow us to
use lower temperature water in the final delivery system because they work so well.
TUBING
Why 1/2" pex vs 5/16 used in quicktrack or roth panels?
Half inch pex has less friction than the smaller tubing. Even though it costs more, we end up being able to run the system
with smaller pumps since we get better flow.
Why use hepex instead of aquapex?
Hepex allows the use of cast iron piping. This includes the low loss header and the black piping and the cheaper pump. If
a stainless low loss header was readily available, it would be possible to pipe the manifold in copper and use a brass
circulator pump, thereby eliminating the need for the hepex. However, even then, we would still use hepex in case some future
plumber replaced the circulator with a non-brass one. This would be likely to happen since the brass ones are 5 times the cost
and not typically stocked in the back of a service technicians truck.
Why use hepex instead of the al-core?
Hepex uses the same fittings as aquapex. This limits the special tools needed to the normal pex expander tool.
LOOPS
Why is there a loop in the downstairs hall but not the upstairs hall?
There is more heat loss near the front door. And people take off their shoes when they come in the house and like
to step onto warm floors.
Why is are all the mud jobs in their own individual loops even though they are small?
It allows for better control. It is worth the extra cost of the fittings.
How many loops?
30 loops were used. Most loops were under 300 feet, and only a couple were slightly more. None were over 350 feet.
Some rooms had multiple loops.
Why not more than 30 loops?
Since each loop needs a run out to the room and back, it is more efficient to use fewer tubes. And overall complexity
of the system increases with more loops.
Why not less than 30 loops?
Keeping tube length under 300-350 feet with 1/2 pex allows the use of low wattage circulators. And since each loop
can be throttled separately and even potentially zoned separately, more tubes allow for better control.
Why run all the loops to the basement instead of having separate manifolds by floor?
Centralized control makes maintenance easier. Since we were able to keep the manifold near the center of the
basement, and since this house is not a sprawling ranch, the longest runout is only 30 feet, so there would be little
to gain by spreading out the manifold to different floors.
Is it a problem that the loops are not all the same length?
Balancing the system depends on the heat loss of the rooms and the length of the tubes. Unless the length of tubing
is matched to the heat loss, throttling will be necessary anyway. We tried to match the amount of tubing to the
loss, but we installed high quality balance valves to be able to fine tune the results.
Why insulate the run outs?
Since the tubes run through walls in conditioned space, insulating them was less important than it would be otherwise.
However, we still insulated them so that we would be putting heat exactly where it was needed which is typically NOT on
an inside wall.
Why does the supply go to the outside walls first.
Heat loss is highest on exterior walls. That is why radiators and baseboard heating is typically installed on outside
walls and not inside. We did the same thing with radiant floors, concentrating the tubing near the outside walls where
it is most needed.
Why the strange patterns in the rooms?
As the hot water flows through the tube, it transfers heat to the room and therefore cools down. The start of the loop
therefore gives off more heat than the return end. By designing the tube layout to match the needs of the room, we
deliver the heat where it is needed.
Why not run tubes in the entire floor of a room?
If we put as much heat in the center of the room as along the outside walls, the room would overheat before the perimeter
would be warm enough.
Why are there so many loops in the master bedroom?
The master bedroom has 3 exterior walls and a door to the terrace, therefore it needs more heat than the other bedrooms.
Additionally, since it is the master bedroom, we wanted maximal control. For this reason there are separate loops for the
closet and the area outside the bathroom. The bathroom is of course on its own loop. The perimiter of the room is a separate
loop and the interior is a different loop, allowing precise control of the entire living space.
Do the tubes run under the beds?
In general, no. Where we could anticipate a bed placement, we ran less tubing. The exception is the master bedroom where
we ran tubing everywhere.
Do the tubes run under the kitchen cabinets?
No.
BOILER
Why a modulating/condensing boiler?
This is the latest and greatest in boiler technology. It adjusts the firing level to match the need (modulates) and
it allows very little heat to escape via the exhaust (condenses).
Why doesn't the boiler need a chimney?
The exhaust is clean and cool and safe, and can be vented out of the side of the house.
Why Viessmann boiler?
This is the top of the line in German technology. Outstanding craftsmanship and real value. Great support.
Very expensive, though.
Why the Vitodens 200?
The Vitodens 100 would have been enough, but the 200 has more features and is more fun.
Why not a bigger one than the 6-24 (the smallest 200)?
We had to hold our breath and resist the urge to supersize everything. This one is big enough.
With a heat loss of 60K, why use a 90K boiler? Why not a smaller boiler?
We needed a big enough one to produce enough hot water for simultaneous hot showers.
Why does it use an outdoor sensor to control the inside water temperature?
It makes hotter water when it is colder outside.
MANIFOLD
Why not use the standard manifolds made by Uponor or Embassy?
We wanted industrial quality balance valves.
Why use black pipe on the header?
We see this most often. Could have been copper, though.
Why 1 1/4 pipe in the header?
If you look at what it is supplying, thirty half inch tubes, the 1 1/4 size seems about right. In fact, though
it is overkill and 1" pipe would have been plenty since none of the half inch tubes will ever need as many
gallons per minute as the tube could deliver. This delivery system could delivery many times more heat than will ever
be needed.
Why so many drain and isolation valves?
It makes it easy to purge the system and to replace components.
Why is there an isolation valve on both the return and the supply zones?
The manifold can be drained and worked on without draining the loops and without needed to repurge them.
Why use one pump instead of one on each zone?
Less energy used.
Why such a low-power cheap pump?
Easy to replace, cheap to operate.
Why use all the balance valves instead of ball valves?
The system works so well we could have just used ball valves. But the industrial quality balance valves
give us finer control.
Why use a Low Loss Header?
This avoid the need for primary/secondary piping and places low loads on the pump.
Why a pressure bypass valve?
If only one zone is open, we don't want to make the pump work too hard.
Why a spirovent?
Great way to keep air out of the system.
Why a LWCO?
Protects the expensive boiler.
Why 15 lbs pressure?
We need about 12 to get up to the third floor and then an extra 3 for headroom.
Why do all the loops use the same water temperature?
The mud jobs will get warmer than the floors, but people like the feel of warm tile. Keeping one
temperature vastly simplifies the complexity of the controls. Keeping that temperature low cuts
energy usage. If the mud jobs were on a seperate (lower) temperature, it would be slightly
more efficient but the added complexity of the controls and zoning would probably negate that
benefit.
If all the loops use the same water temperature, won't the slabs get too hot?
Yes. They need to be throttled back relative to the wood floor loops.
INDIRECT
Why a Vitocell?
This is an amazing piece of German stainless steel engineering. We couldn't resist spending the
extra money.
Why 1 1/4 piping?
As with the tubing, the vitocell is capable of delivering much more hot water than we are expecting
to be asked for. If in the future a large boiler was connected, the 1 1/4 tubing would be useful.
Now it is overkill.
Why not more or less than 90 gals?
It is a good size. To supply more hot water, we would suggest adding a second tank to the supply
end of the first and using solar power to preheat it.
ZONES
Why not more than 6 zones?
We ran thermostat wire for additional zones if desired.
Why not less than 6 zones?
Multiple zones can be synced to effectively run as fewer zones. When we started up the system we
treated it as one big zone.
Why so many sensors?
Sensors in all the loops except the basement walls mean that very fine tuning is possible.
Why Tekmar zone manager?
It is the smartest zone manager we could find.
Why Tekmar thermostats?
PID controls allow precise control of temperature.
