Hydronic heating through the HRV supply air

These are products I'm considering that deliver space heating through
the supply airflow. The heat source is the hot water heater. The
heat gets into the airflow using a hydronic coil (like a car
radiator). In Europe they can buy a compact heat-pump unit that does
all of this in one package. In the U.S., we've had to cobble this
together from different parts. Some complete products are now
available that also incorporate the ERV/HRV.

1. NTI (Nyletherm) Matrix. Complete ERV, condensing gas hot water
heater, and hydronic coil.

2. Lifebreath Clean Air Furnace. ERV and hydronic coil, but supply
your own hot water.

3. Nuair heat recovery air handler. Like the Lifebreath, supply your
own hot water.

4. Turbonics, Inc. HDX-17 and HDX-34. These are hydronic fan coils
that would fit in the supply airflow from the HRV. Designed for 120ºF
water. John Mann at HeatWave Radiant Supply in Ceres.

5. Atrea "Duplex RK2". Designed for passivehouses. Incorporates the
hydronic coil into the HRV like #1-3 above. This is one of dozens
available in Europe, but available in the U.S.? Most likely not.

George points out that the first three products are designed for
heating loads much higher than for a passivehouse, so the components
are oversized and need adjustment to fan speed and water flow rate or
temperature. Number four could also be tailored to a passivehouse

Is there anything else available off-the-shelf? Is it worth shipping
a heat pump unit from Europe? (The refrigerants are different--they
use propane!--and the voltage is different.) While we're dreaming,
why not import this one:

6. NIBE Fighter 410P. Complete ventilation with heat recovery, hot
water, and space heating in one refrigerator-sized appliance.


People in the US drool over the Passive House "magic boxes" that are
available in Europe (justifiably so.) My understanding is that
importing them is not an option. Apparently the frequency difference
(50Hz vs 60Hz) between US and European power causes them to catch fire

Mike LeBeau at Conservation Technologies (http://www.conservtech.com/)
has done work on this with Passive Houses in Minnesota. Apparently,
there are some companies (USA coil and air http://www.usacoil.com/)
which make fan coils to spec - George is correct that most
"conventional" systems are oversized for PH.

It is important to compare the efficiency (both heat recovery % and
electric consumption) of the HRV units. My understanding is that the
Recouperator is the most efficient unit in the US market, on par with
European units. Many US units are far less efficient.

Graham Irwin
Remodel Guidance

Residential Design • Plans & Permits • Green Building • Period

I will try and breath new life into this 1 year old discussion.
I am actually in the process of designing a HRV supply air heating scheme for a retrofit house in Oakland.
Here are the top level specs:
* 1 person household (older lady)
* 3300sqft house
* 3 levels (1100sqft each level)
* 1st floor is 1-2ft in the ground [1/2 basement]
* Envelope will be retrofitted to T-24 levels [and better in places]
* Basement floor and wall is insulated with 2inch closed cell foam
* Windows will be generic Home Depot vinyl double glaze, low-e
* Client is clear that this scheme of heating will NOT be sufficient for design temperature. 3 sealed combustion fireplaces and possibly portable electric heaters will be utilized to "pick up the slack" where desired.
* ACH target for the house is 2ACH@50
Here is the plan:
Use a Zehnder HRV "Comfoair 550" for the house
Use the tank water heater [4ft away] as a heat source
Use water to air heat exchanger to heat the supply air stream
Use a variable speed pump to supply the required hot water
Control unit??

Here is what I will need:
Which water to air heat exchanger will I want to get for this client?
Which pump do I want to use?
What is the best way to control this pump?
Should I increase the airflow for reasons of heating?

BAS ==> 3300sqft*8ft*0.35ACH/60 = 154cfm
More for odor events and parties, less for vacation of course.
Heat demand according to PHPP: 7,8kBTU/(ft²yr)
Heat Load according to PHPP: 12.5BTU/(ft2hr)
==> Demand for house 25,740kBTU/yr
==> Load for the house 41,250BTU/hr
How much airflow WOULD I need: 41,250BTU/hr ==> With an assumed delta T of 40F, 41250/(40*1.08)=950cfm CANT DO THAT!!!
How much heat can I reasonably deliver:
@150cfm ==> 6500BTU/hr
@200cfm ==> 8600BTU/hr
@300cfm ==>13000BTU/hr

What I will do for the rest of the heat is to utilize the fireplaces and move the heat through the house with the ventilation air. Supply air pushes the heated air away from the fireplace to the other rooms [return vents or pass through rooms].

Let the party begin.


The Zehnder HRV "Comfoair 550" puts out 550 m3/h airflow = about 330 CFM. At 40 degF deltaT to room temp you get (1.08 x 330 x 40) = 14,256 BTU/hr. This would be distributed throughout the house based on diffuser locations.

But by ASHRAE 62.2, you only need 90 CFM continuous fresh air in this house by mechanical ventilation. The core of the passivehouse concept is to improve your envelope and other parameters until you can heat the house with only 90 CFM. (1.08 x 90 x 40) = 3888 BTU/hr. With compact geometry and few windows (other than unshaded south) and enough thermal mass, you can do this.

Stefan, if the peak load is 41,250 BTU/hr (in the range of conventional furnaces and typical California houses), you can get 4000 to 14,000 BTU/hr from heating the ventilation air, and the remaining 37 to 27 kBTU/hr would come from your three fireplaces distributed in the house.

We're using the Rinnai RHFE-750 on a current project. It's direct vent (no air pressure imbalance) with a single envelope penetration, about 75% AFUE, 8-22 kBTU/hr output. The list price is about $3500. Rinnai also has direct-vent gas room heaters from 8 to 38 kBTU/hr. Any other brands?

This may be an OK model for California retrofits? With a lower peak load, you can decrease the supplemental, point-source, gas heating.

Dan Johnson, Arkin-Tilt Architects

Made a lot of calls today and thought I update people on the results.
Found a water to
Air heat exchanger from Turbonics that should do the trick
[HDX-36/12 H] http://turbonicsinc.com/catalog_files/HDX%20files/HDX_BROCHURE_2.pdf
A pump with temperature sensors for water (in and out) and external air temperature, suitable for potable water from HBXcontrols.com HYD-0100 http://hbxcontrols.com/products/hyd-0100.php
The guy I spoke to is Bill [209.860.7970] Lead time for these products is in the 1 week range.
Cost is ~ $600 for the pump, $750 for the heat exchanger.


I read through T-24 "2005 Residential Compliance Manual" to find out what I had to comply to with this system; here is what I found significant.
Some graphics are missing, if you are so inclined, contact me and I can send you the file I made for this.

In short, I don't see requirements that prohibit the use of sealed combustion fireplaces as the main heat source.
Zoning is encouraged in the code.


4.1.5 Common System Types

Although the Standards focus on the typical system, they also apply to other
systems as well, including hydronic systems, where hot water is distributed to
provide at least some of the heat to conditioned space; in contrast with
conventional systems that distribute heated air to air heat the space.

4.2.1 Mandatory Measures
The current Appliance Efficiency Regulations require that the Annual Fuel
Utilization Efficiency (AFUE) of all new central furnaces be at least 78 percent
for equipment with output capacity less than 225,000 Btu/hr.

Equipment Sizing
The minimum size of residential heating systems is regulated by the California
Building Code (CBC), Section 310.11. The CBC requires that the heating
system be capable of maintaining a temperature of 70ºF at a distance three feet
above the floor throughout the conditioned space of the building.

4.5.2 Zonal Control
An energy compliance credit is provided for zoned heating and air-conditioning
systems, which save energy by providing selective conditioning for only those
areas of a house that are occupied. A house having at least two zones (living
and sleeping) may qualify for this compliance credit. The equipment may consist
of one air-conditioning system for the living areas and another system for
sleeping areas or a single system with zoning capabilities, set to turn off the
sleeping areas in the daytime and the living area unit at night. (See Figure 4-16).
There are unique eligibility and installation requirements for zonal control to
qualify under the Standards. The following steps must be taken for the building
to show compliance with the Standards under this exceptional method:
• Temperature Sensors. Each thermal zone, including a living
zone and a sleeping zone, must have individual air temperature
sensors that provide accurate temperature readings of the
typical condition in that zone.
• Habitable Rooms. Each habitable room in each zone must have
a source of space heating and/or cooling (if zonal credit for
cooling is desired) such as forced air supply registers or
individual conditioning units. Bathrooms, laundry, halls and/or
dressing rooms are not habitable rooms.
• Noncloseable Openings. The total noncloseable opening area
between adjacent living and sleeping thermal zones (i.e., halls,
stairwells, and other openings) must be less than or equal to 40
ft². All remaining zonal boundary areas must be separated by
permanent floor-to-ceiling walls and/or fully solid operable doors
capable of restricting free air movement when in the closed

2005 Residential Compliance Manual March 2005
4.6.1 Hydronic Heating Systems
Hydronic heating is the use of hot water to distribute heat. Hydronic heating is
discussed in this compliance manual as an “Alternative System” because it is
much less common in California than in other parts of the United States.
A hydronic heating system consists of a heat source, which is either a boiler or
water heater, and a distribution system. There are three main types of hydronic
distribution systems, and they may be used individually or in combination:
baseboard or valence convectors, hot water air handlers, and radiant panel
heating systems. These three options are illustrated in Figure 4-17.
• Baseboard/valence convectors are finned tubes that run along
the base or top of walls. A metal enclosure conceals the finned
tubes. Convectors do not require ducting.
• Air handlers consist of a blower and finned tube coil enclosed in
a sheet metal box (similar to a typical residential furnace), and
Page 4-38 - Building HVAC Requirements – Alternative Systems
2005 Residential Compliance Manual March 2005
may be ducted or non-ducted. Air handlers may also include
refrigerant coils for air conditioning.
• Radiant panels may be mounted on or integrated with floors,
walls, and ceilings. Radiant floor panels are most typical. See
the separate section below for additional requirements specific
to radiant floor designs.
Mandatory Requirements
For hydronic heating systems without ducts, the mandatory measures cover only
pipe insulation, tank insulation, and boiler efficiency. Otherwise, for fan coils with
ducted air distribution, the mandatory air distribution measures also apply as
described earlier in this document. And for combined hydronic systems, as
described below, mandatory water heating requirements also apply to the water
heating portion of the system.
§150(j) Water System Pipe and Tank Insulation and Cooling
Systems Line Insulation
The typical residential hydronic heating system operating at less than 200° F
must have at least 1 in. of nominal R-4 insulation on pipes up to 2 in. in diameter
and 1.5 in. of insulation on larger pipes. For other temperatures and pipe
insulation characteristics see Tables 150-A and 150-B in the Standards.
There are a few exceptions where insulation is not required: sections of pipes
where they penetrate framing members; pipes that provide the heat exchange
surface for radiant floor heating; piping in the attic that is covered by at least 4
inches of blown insulation; and piping installed within walls if all the
requirements for Insulation Installation Quality are met (see the envelope
If the system includes an unfired hot water storage tank, then the tank must be
either wrapped with R-12 insulation or insulated internally to at least R-16. may be ducted or non-ducted. Air handlers may also include
refrigerant coils for air conditioning.
• Radiant panels may be mounted on or integrated with floors,
walls, and ceilings. Radiant floor panels are most typical. See
the separate section below for additional requirements specific
to radiant floor designs.
Mandatory Requirements
For hydronic heating systems without ducts, the mandatory measures cover only
pipe insulation, tank insulation, and boiler efficiency. Otherwise, for fan coils with
ducted air distribution, the mandatory air distribution measures also apply as
described earlier in this document. And for combined hydronic systems, as
Building HVAC Requirements – Alternative Systems Page 4-39
2005 Residential Compliance Manual March 2005
§123 Requirements for Pipe Insulation

Figure 4-17 – Hydronic Heating System Components

Figure 4-18– Combined
Hydronic System with Water Heater as Heat Source
Page 4-40 - Building HVAC Requirements – Alternative Systems
For pipes in hydronic heating systems that operate at pressure greater than
15 psi, the requirements of §123 apply. These are the same requirements that
apply to nonresidential piping systems.

I read through T-24 "2005 Residential Compliance Manual" to find out what I had to comply to with this system; here is what I found significant!!pandora bracelets
Some graphics are missing, if you are so inclined, contact me and I can send you the file I made for this!!pandora jewelry
In short, I don't see requirements that prohibit the use of sealed combustion fireplaces pandora as the main heat source.
Zoning is encouraged in the code.

The NTI (Nyletherm) Matrix looks pretty good. Back in the day
Lennox? had a condensing water heather with hydronic air handler built
in (the Canadians may have had one too). There was a U.S. company that
had a HRV hydronic air handler combination (John Bower, Ventilation,
1995 shows it).

I could not find electrical data for the Matrix, but it can run as
low as 300 CFM on heating, with a heat output of 12,000 Btu/hr at 180deg
F water temperature. This gets us in the range of heat loss. Nabih's &
David Gerstel's houses are in the 12-15 kBtu/hr range (my house as well
when done), Manual J, or ASHRAE 90.1. Although the PHPP would show
5kBtu/hr +/- roughly (due to internal gains and less safety factor?

The Matrix, Lifebreath & Nuair all come from the Canadian
governments comfortable initiative. I was unaware of the Matrix, thanks
Dan! I knew they were being developed.

The matrix looks like a Munchkin boiler with a HRV & hydronic air
handler. And you can do DHW & hydronics (floor, baseboard, etc.). Looks
like a winner.

The downside? cost? no solar hot water contribution except for the
DHW. Upflow design only (Nuair also).

It's difficult when the loads get so low, I had to increase my CFM
on David Gerstel's house, so the smallest registers would work (barely),
not complaints, and were in our second winter! (2x6 24oc OVE framing).
Total energy use is close to the 120 kWh/yr/m2 (depends partly on source
energy conversion).

I'm not yet sure what the best system(s) are, but I've been working
on it.

George J. Nesbitt


It is important to know the efficiency specs when comparing these
units. PHPP recommends a "counterflow" vs a "crossflow" heat exchanger
with a "energy recovery efficiency" >= 75% (PHPP 2007 manual, p. 14)
and typically subtracts 12% from the manufacturer's stated heat
recovery value (PHPP 2007 manual, pp. 29 & 87)

Also, the efficiency of the fan motors must be considered. Since this
unit presumably runs constantly, inefficiency can wreak havoc on the
source energy limit. ECM motors are probably the only option, and even
then I would check the ratings.

Again, the UltimateAir RecoupAerator is the unit PHIUS (and Nabih)
have used. It is probably wise comparing these other units against
it's specs: http://www.ultimateair.com/Ultimate_Air/specifications/house_unit_specs....

Lastly, I have heard of people developing tempering systems with pex
tubing placed UNDER the slab and glycol run through a thermostatically
controlled pump and fan coil at the input to the HRV/ERV. It's a bit
like an "earth tube" tempering system, but without the condensation
and mold concerns. In many cases, getting the outdoor air to 50/60ºF
before it even gets to the heat exchanger can be a big help, winter
and summer...

Graham Irwin
Remodel Guidance

Residential Design • Plans & Permits • Green Building • Period

I agree, and all decisions on equipment and building systems should be
made with the the PHPP informing the decision.

I'll pass on drooling over the European equipment, and stick to North
American! and maybe some Japanese.

The HRV efficiency is 72% (12% will be automatically deducted because it
has not been "certified" by PH, and is a problem as we bring PH to the
North America). I have not found the electrical data, by I can guarantee
you it is an ECM motor.

There is confusion about the PH "requirements", it has come up in my
GreenBuilding Listserve recently, and even in our group. There are
"Requirements" and there are "principles" or "guidelines". HRV is not
"required" for PH, but I would say highly recommended.

I have read through page 56 of the PHPP manual. The 75% HRV efficiency
and fan watt draw are "recommendations" for the central Europeans
climate. Our task is to define the "prescriptive" "recommendations" for
California's Climates.

George J. Nesbitt


The HRV efficiency is 72% before or after the deduction? To which HRV
are you referring? The Recouperator's stated efficiency is 90%, which
is why you get to 75% with deduction. Many US products aren't even
close to this level, don't ask me why, I'm sick of speculating on that.

The ONLY requirements of PH certification do not include HRV, they are:
15 kWh/m2a maximum heating and cooling demand
120 kWh/m2a maximum total source energy
0.6 ACH @ 50 Pa maximum air leakage

Everything else is a recommendation, which is the beauty of the
approach, IMHO - very "unprescriptive."

I am inclined to believe that an efficient HRV is important for
reaching PH standard economically. I refuse to participate in the
development of anything "prescriptive" for PH. I am eager to help
develop proven and tested "best practices," "solutions," and
"recommendations" unique to our circumstances.

Graham Irwin
Remodel Guidance

Residential Design • Plans & Permits • Green Building • Period

Matrix 72% (PHPP deducts 12% 72-12=60%)
Recouperator 95% (ERV, sensible + latent load, rated (95-12=84%)

I agree, minimal requirements, and flexibility on how you meet them is
great. Our CA energy code is similar.

Sorry, maybe I should have not use the term "prescriptive", but many of
the things people confuse as "requirements" are the list of
"recommendations" for the central European Climate on performance
thresholds that they may need to achieve to reach the "standard" or

And our job is to define those "recommendations" or "guidelines" for CA
and all 16 climates!

This sound too much like a PHPP discussion, we should start a "group"
for that one!

George J. Nesbitt

Yes, I agree, a good and relatively narrow set of best practices, soultins
and recomendations are what we need. As long as we structure them well so we
do not confuse it more than necessary.


Hi All, I've uploaded a new diagram to the Group website. It shows
the draft mechanical configuration for our net-zero energy project in
Palo Alto. The file is called "Combi DHWspace heat
diagram_20090119.pdf" Here's a direct link:

I've sent this to a hydronic supplier for comments. I'd appreciate
anyone else's input. Thanks.


1) How is it that this house will be made "net zero energy" if you're
using natural gas? Will you apply some equivalency to excess
photovoltaic output which compensates?
2) You'll have to take steps to ensure that the potable water being
mixed with heating water doesn't cause health problems and/or building
inspector upset. My understanding is that some jurisdictions permit
this and others don't - the concern being that water in the hydronic
heating loop stagnates during non-heating periods.
3) I have heard reports (Gary Klein from the CEC a primary source)
that tankless water heaters are nowhere near as efficient as generally
assumed. The problem is that the device has to cycle for any hot water
draw, and most of the DHW draw in a typical home is in short "events"
which are so small that the large burner in the tankless basically
just fires up and stops, and the efficiency plummets - I equate it to
using a 747 to taxi down the block to the corner store and back. The
debate continues, but my understanding is that if the household uses a
tank of hot water or more a day, the standby losses from a storage
tank are less than the cycling losses of a tankless. I would recommend
a solar-compatible storage type water heater with a modulating boiler,
such as the Phoenix, or an air-to-air heat pump integrated with the
solar storage tank which comes from the solar supplier (almost all of
these tanks come equipped with an electric resistance element whether
you want it or not.) You might also find that you can offset the
backup solar thermal energy with PV, even if using electric
resistance, but gas or heat pump will make it about 3 times easier...

Graham Irwin
Remodel Guidance

Residential Design • Plans & Permits • Green Building • Period

Thanks for the feedback. Unfortunately I think to improve the system,
we need products that are not available. Agreed? (With the possible
exception of using the Phoenix gas water heater--I'll update the
diagram with this). My replies to Graham's points:

1) Gas is being offset at a rate of 1 kWh PV production = 3413 BTU of
gas consumption. This is the most conservative theoretical way to do
it, but I'll admit that you really can't offset burning natural gas.
And 1 kWh electricity run through a heat pump will make 7000 to 10,000
BTU of heat, so why not go all-electric?
A) Because PG&E is burning gas at the power plant to make electricity
in the first place.
B) I just searched for an hour for a suitably small, cheap, ducted
air-to-air heat pump and couldn't find one
C) What we really need is an air-to-water heat pump as backup for the
solar hot water (and hydronic space-heating downstream). How about a
pair of 7000 BTU/hr AirTap water heaters?
(http://www.airgenerate.com/products/specs.html) I cringe at the
installation gymnastics you'd need for these units, and the noise
they'd make. Otherwise you've got the Unico RC chiller, but it's
oversized (http://www.unicosystem.com/Portals/0/Pdf_Files/UniChillerRCBrochure11300...)
and too expensive.

2) I believe potable water is permitted in a hydronic coil but not in
a radiant floor; the coil pump has to run for a minute every six hours
to keep the water fresh. A pump-cycler control will do this. The
alternative is a heat exchanger to separate the hydronic loop from the
potable circuit (then you need higher water temp and two pumps).

3) I agree the tankless have flaws, but they're the cheapest, most
efficient way to make heat from gas. We'd rather use the Phoenix,
which integrates a buffer tank for better performance, but it's more
expensive (http://www.htproducts.com/phoenix.html). We might end up
with the Phoenix just because it's a condensing boiler and needs only
a PVC vent, while a standard tankless like a Takagi will need a steel
flue with clearance to combustibles, so the total install may be
cheaper with the Phoenix...any opinions?

Thanks, --Dan


A few other thoughts:

1) The device you are seeking is called an "exhaust air heat pump"
water heater or a "heat recovery water heater." These are available in
Europe, where they are sometimes installed as the last item in the
exhaust air stream to "squeeze" every last bit of energy out of the
conditioned exhaust air, as in this diagram (taken from http://www.passivhaustagung.de/Passive_House_E/compact_system_passive_ho...)

I am aware of a couple such units in the US:

http://www.thermastor.com/Heat-Recovery-Water-Heaters/ which is used
in commercial installations, so it may be oversized and/or unsuitable
to the task, I haven't explored it much. Here is a report on them

It may be that the airflow required for these units will far exceed
that required by the Passive House, so these devices may be
"oversized" for such an application.

2) I have heard that the Airtap heat pump water heaters are noisy, but
have no direct knowledge. My understanding is that they are quite
reasonably priced. If one were forego trying to duct it, and simply
install one inside the conditioned space, you would cause cooling
there, which would raise the heating load in Winter, but lower the
cooling load in Summer - it might be worth exploring whether the
balance was in your favor - my work so far in our climate suggests
that Summer cooling is as much a concern as Winter heating. I believe
they also have some facility for redirecting the cooled air to the
exterior in Winter.

3) The potable water integrated with the heating system is, to my
understanding, subject to whomever is inspecting your project - some
jurisdictions allow it, others don't but I am no expert in the
implementation/installation - there are others in the group who are...

4) Your airflow rate seems high to me @ 210 CFM. The Recouperator runs
from 70-200 CFM, so you're asking for more than it's top output to
deliver your peak heating load. The "magic" number for peak heating
load with Passive House is 10W/m2 (~1W/ft2, 3.17Btu/hr.ft2) where the
heating load can be delivered through the ventilation air. Is this
where your shell design is taking you? It may be worth increasing the
shell's efficiency to reduce the peak heating load, especially because
of our milder climate and the fact that you're aiming for zero energy,
which means that any savings you don't get through the shell you pay
for with a larger PV system, and that's an expensive tradeoff. Passive
House was designed to deliver the most cost-effective balance between
efficiency and construction cost, but that is based upon European
climate and does not assume net zero energy as the goal. If your peak
heating load exceeds the capacity of the ventilation stream, you might
forego trying to use that airstream at all and install radiators, etc.
You might also consider a direct vent gas fireplace for the really
cold times...

5) When coupled with some further efficiency analysis as above, you
may find that the backup resistance element in the solar thermal tank
isn't a huge load to offset with PV, and that the savings brought by
eliminating the backup heater (the resistance element comes with most
solar thermal systems "for free" anyway) can buy the extra PV panels.

6) Likewise, analyze the cost of larger PV system vs the cost of the
Phoenix compared to the tankless and see where you come out.

Interesting project!!!

Graham Irwin
Remodel Guidance

Residential Design • Plans & Permits • Green Building • Period

Interesting concept with the Heat pump water heater in these homes (http://www.ashrae.org/docLib/20081021_smallbuildingapps.pdf
) The feed to the HPWH was switched between the kitchen refrigerator
coils and the conditioned crawlspace for cooling and heating seasons,

Graham Irwin
Remodel Guidance

Residential Design • Plans & Permits • Green Building • Period

Thanks Graham. One comment that may be interesting for the group:
I believe the max airflow on the Recoupaerator is 210 CFM (I'll have
to check the spec sheet) so we arrived at a max heating load of 8500
BTU/hr using 210 CFM and a 110 deg-F supply air temperature. Now
we're designing an envelope that delivers a heating load of 8500 or
less. This is the reverse of the typical process: we're sizing the
envelope to meet the load instead of the mechanical equipment. I
believe this may be a better process.

I had some conversations today that made me consider the merits of
electric resistance backup hot water (like Graham suggests) and
electric baseboard heat. In this case, our heating load becomes
un-linked from the supply air flow (which can remain at a low 80 CFM
by ASHRAE 62.2 minimum ventilation air). Then we can go higher than
8500 BTU/hr, but we start paying penalties in our source energy
requirement and net zero goal.

Thanks Dan, are you sure you are an Architect?

1. Load calculations; ASHRAE or Manual J load calculations for
heating do not include internal loads, and I have heard the safety
factor is as much a 60%! The PHPP does include internal loads and
probably does not have the same large safety factor. So that would
explain the large differences.

2. The 10 W/m2 recommended heating load is based on...

3. Yes the ERV only delivers 210 cfm, and your calculation is
correct (Btu = cfm x 1.08 x delta T). So if you needed more heat you can
increase the cfm, or the delta T! And we have not converted Nabih's
house from electric baseboard to hot water yet. I am waiting for answers
to the PHPP.

4. Duct design for architects; the more air, the longer the ducts,
the more fittings and direction changes, the larger the ducts need to be
(please design space for us to install them!). The cfm and velocity of
the air at the register is related to the size and style of register you
use, and how far it "throws" air into the room and mixes the air, and
how much noise it makes, and how comfortable it is. My cfm's were too
low for the smallest grills for Gerstel's house, that why I increased it.

George J. Nesbitt

Mechanical equipment should be designed to the envelope, but most of the
time is not. Design the envelope to the mechanical equipment works too,
and should be done, but also is not done most of the time either. It's a
chicken and egg situation, which comes first, when in reality they both
have to exist.

Design with the mechanical systems in mind, design the mechanicals based
on the design, etc....

Electrical backup to solar hot water makes some sense, but instantaneous
makes more, why heat what you don't need?

While with small loads you may be able to heat with electric baseboards,
I would discourage it. You take a hit on CA T24 as well as with the
PHPP. While from a site energy standpoint 100% efficient electric is
more efficient than any gas heat, you take a big hit based on source
energy. If you go electric, you have to think about heat pumps, and we
can add that into the ventilation system too.

George J. Nesbitt

Assuming that you are applying for a building permit this year, you must use the 2008 version of the Title-24 Energy Code. Your quotes from the 2005 Code are irrelevant.
Have you checked with the building department to see if they will allow wood stoves to be the primary heat source, some will not , due to air quality issues. The Energy Code does not prohibit wood heat, however.
Also, I looked at the referenced info for the Turbonics & HBX Controls but saw no indication that this equipment is certified for use with potable water. Are you sure about this? Do not rely on what some salesman told you on the phone, get it in writing.
Patrick Splitt - CEA

Why not distribute inexpensive electric wall heaters, etc? There are many nice looking ones available. Does this exceed the energy budget?

Also, what standard is used to rate the efficiency of that fireplace? My experience is that many manufacturers fudge the numbers on the efficiency. The GreenPoint Rated recommendation for efficient fireplaces is to use a Canadaian efficiency rating system. "Canadian Standards Association CSA-P.4.1-02 standard. Testing to this standard produces a fireplace efficiency, or FE, rating. The FE rating is a more accurate measurement of fireplace energy efficiency than “annual fuel utilization efficiency (AFUE)” or “steady state.” Thus the FE rating is the only recognized measurement of vented gas fireplace energy efficiency in Canada."

You can find the homepage for the database here:


I have looked into many of the top efficiency ones and they look very nice. Some of these natural gas models are as high as 90.5% - wow!



I agree with Kris Knutson. If inexpensive electric wall heaters are distributed then they will be not only be nice looking but also reduce the budgets of energy. I recommend these heaters.

Flexible Duct

HDX units use L/ASTM B75Copper and
have been IAPMO tested and passed
ANSI/NSF 61 Section 4 percolation test
and are therefore suitable for use with
potable water systems.

Sample Specification:
Unit(s) with the necessary output to supply the load in each installed
area shall be mounted within a suitable location that provides access for
servicing and may be connected to a properly designed and balanced
ducting system. Includes closed cell Insulated cabinet & optional Condensate
Drain Pan (cooling applications only), copper coil with L/ASTM
B75Copper and aluminum fins (or comparable material) tested in accordance
with ANSI/NSF 61 Section 4 percolation test and suitable for use
with potable water systems. Maximum water temperature of 200°F, and
a pressure rating up to 125 psi. Propeller style fan is desired to provide
quiet operation and easy cleaning, service or replacement. Unit must
include 3-speed shaded 4 pole motor and may be controlled with remote
wall mounted thermostat and/or variable speed fan control. Unit(s) to
have minimum of CSA approval. 5 year limited manufacturers warranty.
Locking screws for cover if required are supplied by others.