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Star How to select the best Heat Recovery Ventilation system for your house.


Basic principles

A sealed house needs specific ventilation designed in

The house will be (and for energy efficiency needs to be) tightly sealed, ie highly air tight.  This gives you complete control over the air coming into your house (which is a very good thing), but it's important to make sure there is air coming into the house so you don't suffocate or feel groggy.  You need either an ERV (Energy Recovery Ventilator) or an HRV (Heat Recovery Ventilator).

Even if you cannot afford the $600 - $2000 that an ERV/HRV will cost, you should at least implement the ducting for installing one.  Use a simple inline fan where the ERV/HRV will go until you have saved up the necessary money.

What are ERVs and HRVs?

Both ERVs and HRVs have a heat exchanger that aims to somewhat match the temperature of the incoming air to the temperature of the outgoing air.  ERVs go a little further in aiming to somewhat match the humidity of the incoming air to the humidity of the outgoing air.  The matching process is obviously only possible to a certain percentage, but even so it can have a significant beneficial impact on your energy bill.  In a decent ERV such as from UltimateAir, about 95% of the heat energy from the outbound stale air is transferred to the incoming fresh air (and about 75% of the humidity).


Here's a quote from Martin Holladay at http://www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv :  "If energy efficiency is your most important criterion — and I believe it should be —choose either the UltimateAir RecoupAerator 200DX ERV (which draws 40 watts to deliver 70 cfm) or the Venmar EKO 1.5 HRV (which draws 13.5 watts to deliver 40 to 80 cfm)."  These are both very fine units, but you may decide to choose a cheaper model such as a small Fantech HRV that have starting prices of about $500.

In my area it is necessary to heat the house for well over half the year, so any waste heat from the motor in the HRV/ERV will contribute towards heating the house during the cold months.  Because of this I am less worried about how many watts the unit uses.

In my climate zone (Pacific Northwest USA) the benefits of an ERV over an HRV are fairly small.  There is nothing wrong in using an ERV, but an HRV will do just as well.  I like the UltimateAir RecoupAerator 200DX ERV, but I also like the Venmar HRV EKO 1.5  (http://www.venmar.ca/AfficherProduit.aspx?page=1&id=124&langue=en ).

I ended up choosing Fantech HRVs because they were nicely priced.  For my small evaluation building I used a "Fantech VHR Series Heat Recovery Ventilator w/ Fan Shutdown Defrost, 4" Top Ports" as it was only about $500 from PexSupply.com  (http://www.pexsupply.com/Fantech-VHR704-VHR-Series-Heat-Recovery-Ventilator-w-Fan-Shutdown-Defrost-4-Top-Ports-up-to-1400-Sq-Ft ).

The Fantech unit I chose for the evaluation building can only handle 1400 sqft so is not enough for my main house, but Fantech do provide low cost units that can handle many times that square footage (See full Fantech range at http://www.pexsupply.com/pex/control/category/~category_id=13180/~refine=213180+100257 ).  Not a bad strategy is to use two lower price medium sized units to provide for your square footage because that means you still have ventilation if one of the units fails and needs to go off for repair.  Having separate units at each end of the house can also make the ducting easier.  Having two units is what I decided to do for my main house.

Small Fantech HRV:

Fanteck small HRV 

For the main house I use medium sized units.  These use 6" ducts.  Fantech SHR150 - VHR Series Heat Recovery Ventilator w/ Fan Shutdown Defrost, 6" Top Ports

http://www.supplyhouse.com/Fantech-VHR150-VHR-Series-Heat-Recovery-Ventilator-w-Fan-Shutdown-Defrost-6-Top-Ports    $626.95

HRV Fantech VHR150   Info is here .


Large UltimateAir ERV:

ERV - UltimateAir 

The other thing I like about HRVs is that they are nice and simple.  There is a very obvious box like thing in the center.  The box is a stack of plates that form alternating air channels.  The stale exhaust air is on the even numbered airways and the incoming fresh air comes via the odd numbered airways (getting warmed by the stale air on either side).  You can easily take the box out to clean it if it gets dirty or clogged.

Horizontal Fantech HRV airflow 

Vertical Fantech HRV airflow 

Fantech HRV core removal 



Exhaust from stale and wet areas, Fresh air to living areas

You need both an exhaust exit air path and a fresh air path.  The exhaust exit air should be taken from bathrooms, kitchen, utility room, and from the top of the house living space where old warm air will naturally rise to.  It will be exhausted to the outside.  Filtered fresh air from the outside should be gently blown into to the living rooms and bedrooms.  In a balanced system (which is what you want) there is forced air on the exit exhaust and similar cubic feet per minute forced air on the intake.

Air intake and outlet locations

Obviously you want to site the air intake to be as far away as possible from anything generating pollutants such as a driveway or a sewer vent.  It should ideally be at least 10 feet above grade on whatever side of the house you think has the cleanest freshest air.  The inlet should be at least 10 feet from the inlet and down-wind of the prevailing wind.

In my case the inlet will be on the utility room west wall (north of the door) at main level ceiling height.  The outlet will be on the north wall in the north east corner of the utility room.

Typically you will buy an inlet and exhaust pair, both 6" diameter.

Air external intake and outlet 6in Details are here .


Where to site the ERV

Putting an ERV in the basement is the most common location.  It needs to be in a heated part of the house to avoid condensation issues.  HRVs/ERVs do make some small amount of noise so it wants to be sited away from rooms where you want quiet.  It also has some slight vibration.

I use two HRVs (each 150cfm).  One is in the basement (up near the basement ceiling on a small mezzanine above the stairs) and one in the utility room (on a mezzanine).  They each handle the following areas...

Basement HRV:
    Stale air from:
        Basement bathroom
    Fresh air to:
        Basement east
        Basement west

Utility room HRV:
    Stale air from:
    Fresh air to:



Stale air ductwork

Vents to extract air from damp rooms such as bathrooms, kitchens, and utility rooms should be in the ceiling or at the top of the wall in that room (because warm air rises).  Once it has safely got to the stale air pipe, the fan will take it to the HRV/ERV ok.  In the kitchen, think about how best to avoid the stale air pipe picking up vaporized grease (eg if ceiling height allows, keep it 8 feet above the actual cooking surface).  A filter on the stale air intake grill in the kitchen is also a possible idea (but I'm not doing this).

Air filter box 6in Fantech Details are here .

If you just put a filter on the extraction duct from the kitchen and not on the other extraction ducts then the proportion of stale air coming from the kitchen will be reduced.  You could put filters on all the intakes, but in practice just one filter box near the HRV/ERV is all that is needed.  It is a benefit to have a separate filter box on the stale air into the HRV/ERV because there is a filter box on the fresh air intake from outside and so it is good to provide a similar restriction on the exhaust so the system is well balanced.

Intakes for stale air to the HRV should be provided both high and low in a room. In the winter you open the bottom vents (and close the top) and in the summer you open the top vents (and close the bottom).

Fresh air ductwork

You want to have fresh air provided to all the rooms where people sit or sleep.  The vents providing fresh air should be sited to avoid drafts.  An appropriate spreader vent (as pictured below) will help avoid drafts.

HRV vents for inside Details are here .

The above pictured vents look quite stylish and can also be used as exhaust vents.

On the fresh air intake from outside it is good to have a filter box as close to the outside as possible to avoid bugs and dirt from getting into the inlet pipe.  The following filter box is a good choice...

Filter box Details are here .


Ductwork implementation

You need ductwork that is as smooth as possible inside.  Galvanized steel is a good choice, but 90 degree turns restrict air flow.  I prefer the convenience of flexible ducting.

Route it to avoid condensation, ie slope it downwards towards a drain.  That means the HRV needs to be lower than the stale air vents that go to it.  Insulate around it if routing through a cold area.  Ideally use insulated duct everywhere.

I use 4" to and from rooms...

Insulated flex duct 4in Purchasing details are here .

and 6" to and from outside...

Insulated flex duct 6in Purchasing details are here .

The 4" ducts for the fresh air to the rooms and stale air from the rooms needs to be routed in the ceiling.  The 4" insulated pipes need 6" of space so will not fit in the wainscoting.  The in and out vents need to be up high anyhow so that works well.

The ducts need to be routed with a downward slope to the HRV so that condensation flows to the HRV and then out of the HRV's drain.  That means the ducts need to go down the wall at some point.  That will take a bigger than normal pilaster to hide it.  There also needs to be room for the duct to make the turn from along the ceiling to down the pilaster.  The turn radius is hidden by the polystyrene cornice.

Supe it up with an after-burner

It's not actually an after-burner (although that name makes it sound cool), but it is a good idea to provide the ability to heat the intake air.

May as well heat incoming air

I'm not a big fan of forced air heating, but given that you need to deliver fresh air to the various living rooms and bedrooms you may as well on cold days heat it up a bit.  At the very least it's good to take the chill out of it so room occupants don't get any cold drafts.

Duct heater Neptronic Details are here .


No forced air furnace

In my case I am not using furnace driven forced air heating.  It is electrical heating, but in my area electric power is not too expensive and I don't have natural gas available.  An after-burner on the fresh air delivery contributes to the electrical heating for the house.

Note that for a well designed heating system it is necessary to have a combination of warmed fresh air and air that is recirculated and heated.  You will not be able to economically keep your house at a comfortable temperature by only doing heating of fresh air.  You need some heating that takes air from within the house, heats it, and then returns it to the rooms.

Shutters on some fresh air vents

If there are some rooms of the house that are sometimes not used, then it's not a bad idea to shut-off those fresh air vents so that the heated fresh air is not wasted on those rooms.  You want the warm fresh air to be mainly going to where the people are.  In the primary living room and primary bedroom(s) it is best to not provide a shut-off mechanism so the HRV/ERV always has somewhere to send the warmed fresh air.  The vents I'm using are adjustable so you can close up the vents in rooms that are not being used.

HRV vents for inside Details are here .


Air flow and filtering

Required air flow

A good rule of thumb is to say that you should have an ERV/HRV system that can provide 0.05 CFM for every square foot of finished space in your house.  A house of 4,000 sqft would therefore need 200 CFM.  Even if on a bigger house you install just one then you should implement the ductwork to allow another to be added later.  I'm using two HRVs that each are 150cfm, which is a total of 6,000 sqft.

Air filtering

Most HRVs and ERVs provide both ventilation and filtration.  It captures pollen and mold spores before fresh air is passed into the house.  Even with this (as noted above) it is good to provide a separate filter box on both the fresh air intake and the where the stale air enters the HRV/ERV.

Filter box Details are here .

You need a filter box on the stale air duct as well as the fresh air duct.  As well as stopping dust from the house clogging up the HRV it also helps equalize the input and output pressure.

With my two HRVs, that means I have 4 filter boxes.

You should plan to replace the filters about every 3 months.

Is a separate de-humidifier needed?

It is possible in humid or wet climates, or when having lots of showers or boiling lots of pasta, that you might need a separate de-humidifier unit.  The likelihood of needing a de-humidifier is slightly reduced by choosing an ERV instead of an HRV, but there is still the possibility of needing a de-humidifier.  My advice is to monitor the humidity over the first 6 months of living in the house, and then decide whether or not to get a de-humidifier.



Other HRV/ERV brands

I decided to use Fantech HRVs (as detailed above for price reasons), but here are details of other good choices.


178 Mill Street, Athens, Ohio 45701.


www.UltimateAir.com        info@ultimateAir.com

Jason Morosko        jmorosko@ultimateair.com   

ERV - UltimateAir 

Airflow Capacity:   ~70 – 210 CFM

Dimensions:   25 in. H x 19 in. W x 25 in. D (63.5 cm H x 48.25 cm W x 63.5 cm D)

Uses 6" duct (but output from inline heater option is 8").

The retail price is close to $2000.



Adding air conditioning and heating heat pump

If you want air conditioning with the added benefit of using a heat pump to provide some efficient heating then after the ERV/HRV it is good to add a unit such as the Sanyo unit pictured below.  There is an outside unit that can be placed well away from the house and this connects with up to 165 feet of refrigerant piping to the inside unit that can be placed inline with your ERV output ducting.  Expect to pay about $4K for this system, eg from http://ecomfort.com/31200-btu-36pef1u6-concealed-duct-ductless-heat-pump-system-28475.html .

Sanyo air conditioner and heating heat pump 

Even if you do not put in air conditioning (and I'm not planning to do it because I just rely on all the thermal mass) it is a good idea to allow room for the possibility in your ducting system.


Clothes Dryers

There are three types...  Vented, Condensing and Heat Pump.  My recommendation is to get a Heat Pump clothes dryer.

Vented dryers

These use electricity or gas to generate heat and then exhaust the hot moist air to the outside (loosing all the heat energy).  These are the conventional cheap type of clothes dryers.  Building code requires proper exhaust venting.

Condensing dryers

The main focus of these is to remove the need for exhaust ducting rather than to save energy (although they do save some small amount of energy).

Heat pump dryers

Heat Pump Clothes Dryer LG 

A heat pump dryer captures the hot air, removes the moisture from it, then reuses that already hot air to dry more clothing.  The technology is already reasonably common in the rest of the world, but eg LG's EcoHybrid is actually the first heat pump dryer commercially available in the United States.  The price for this model (number DLHX4072) is about $1,600.

They’re much more efficient than traditional condensation dryers (40-50 percent by some estimates).


Building code

IRC 2003, Section M1501 Clothes Dryer Exhaust M1501.1 General. Dryer exhaust systems shall be independent of all other systems, shall convey the moisture to the outdoors, and shall terminate on the outside of the building. Exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.

IRC 2003, Section P3001, General The provisions of this chapter shall govern the materials, design, construction, and installation of sanitary draining systems. Plumbing materials shall conform to the requirements of this chapter. The drainage, waste, and vent (DWV) system shall consist of all piping for conveying wastes from plumbing fixtures, appliances, and appurtenances, including fixture traps, above-grade drainage piping, below-grade drains within the building (building drain), below-and above-grade venting systems, and piping to the public sewer or private septic system.

IMC 2003, Section 504 Clothes Dryer Exhaust, Section 504.1 Installation Section 504.1 Installation. Clothes dryers shall be exhausted in accordance with the manufacturer's instructions. Exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.


If a condensing dryer or Heat Pump dryer is specified, verify that the proper drainage or an adjacent sink has been provided to remove the condensate.