I am building a new home in northern Wisconsin.  We are installing a HRV system. Dedicated exhaust ducts from 3 bedrooms and laundry.  The issue is the supply ducts.  The HVAC contractor says he wants to dump the supply air into the cold air return on the furnace. He said the air in this part of the country is so cold in the winter that running dedicated supply ducts into living areas and master bedroom would be cold and uncomfortable.  I told him I have read dedicated is the best and that I dont want to use the furnace fan for moving HRV supply air.  He said you dont need to run the furnace fan as the supply air dumped into the cold air return will find its way throughout the house duct work.  I only have a furnace for spring and fall and summer air conditioning as I have radiant floor heat that is my primary heat in the winter.  Another reason I dont plan on using furnace fan often. 

Is what he says correct about it is  better dumping the supply air into the cold air return on the furnace  because  dedicated supply air into the living areas will be cold and uncomfortable  ?   He said he could heat the air on  dedicated supply ducts but that to me is a total waste of energy. 

This has been and is done, but whether this is best/acceptable has been discussed/debated:

Building Science Corporation

Green Building Advisor

Now if you were using mini splits or full-time hydronic radiant floor heating, you wouldn't have to think too hard about this, LOL!

It may be personal preference. The supply air is going to be cooler, but nowhere near as cold as outside air because of the heat recovery. Some people can't tolerate any kind of a cool draft and others don't mind it.

Putting a small tempering coil on your HRV air isn't going to waste energy except as befits the relative efficiencies and fuel costs of your regular heat. All the heat that goes into tempering the air is heat that would otherwise be required inside your house. I would recommend electric resistance coils - remember, they are "100% efficient". :-) It's not much. You're just making up the difference lost to the heat transfer efficiency of the HRV.

You would also have to look into how your particular HRV handles very cold conditions. If the HRV senses cold air entering, it may actually shut down in order to avoid freezing up. I would have expected that HRV installs in your neck of the woods would have tempering coils as a matter of fact, otherwise they will spend good portions of the winter not operating.

ETA: I wouldn't just dump it into the forced air system.

We ERV systems in both fashions but the fan must be running.

In my own remodel I dropped the fresh air into the bedrooms without discomfort since the radiant floors make for perfect comfort in nearly any condition.

In some instances we may use a closet since they tend to get stale and are rarely occupied.

The best method of installing an ERV/HRV is to use its own dedicated ducted system. Anything else is always a compromise and hurts efficiency, performance and comfortability.

Trusting most HVAC installers is like trusting that a car salesman is looking out for your best interest.

I really like the UlimateAir systems. They are USA made and cost a lot less than the high-priced Euro models.

I would not put fresh air from an HRV or ERV into a plenum which only comes on when the thermostat calls for heat. You want it delivered constantly regardless of her mechanicals. We duct the fresh air high on the wall into bedroom closets where it will mix with the room air and not be uncomfortable.

I would not put fresh air from an HRV or ERV into a plenum which only comes on when the thermostat calls for heat. You want it delivered constantly regardless of her mechanicals. We duct the fresh air high on the wall into bedroom closets where it will mix with the room air and not be uncomfortable.

Yes Bob, I agree, I agree, I agree, LOL!

"Trusting most HVAC installers is like trusting that a car salesman is looking out for your best interest."

Yes Lbear, very true an advocating running the HVAC system fan to do this makes great sense if you sell/install the fans too!

Sailaway,

What do you recommend for duct work on an ERV/HRV? I like the flexible duct work since it is easier to install.

Yes, I am a big fan of these newer flexible duct systems as well. Reducing installation cost often allows someone to use a HRV where they might not otherwise do so. HRVs go a long way to achieving an energy efficient home while providing the ventilation we need to stay healthy. Likely more important than the specific duct system is following HRV duct best practices.

could you suggest a good resource in order to read and gain a better understanding of HRV/ERV methods and best practices? Most of what I find is published by manufacturers and is more or less a sales pitch rather than information.

http://www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-much-fresh-air-does-your-home-need.

http://www.greenbuildingadvisor.com/blogs/dept/musings/designing-good-ventilation-system

Green Building Advisor has a lot of info on the topic.

Chris

One other question, the house is a single story with a finished lower. Master bedroom on main and 2 bedrooms in lower. Total sq ft about 2,500. If we dedicate and put exhaust in all three bathrooms and 1 in laundry room, where is it best to put the supply air and how many locations.

Master bedroom ( possibly closet ), main living area and main finished area in lower ?

I posted another question on this thread but I thought I would just ask you.   The house is approx 2,500 square feet.  Main level with a master bedroom and finished lower with two bedrooms.  Two baths up and one down.  If I dedicate, would I put exhaust in three bathrooms and laundry room and where would I go with supply.   Master bedroom closet, main living area and lower finished area ?    I said closet of master bedroom because of other suggestions.

You always want to take out/exhaust the stale smelly air from the bathrooms, laundry and kitchen area and bring in fresh/intake air to open areas so it can disperse throughout the home. You don't want the fresh air dropping in over the master bed area in winter because even with a heat exchanger/ERV, the air will still be colder than the interior room temp air.

In my view, if it drops below 20F at night, just turn off the ERV for the night. Those few hours without ventilation will not do any harm. Unless you live in a 1,000 sqft home with 5 people, I wouldn't worry about CO2 levels.

I put exhaust in the master closet as well because it has no heat and we want the overall circulation to take heat into it. Having a master circulation plan when the larger air handler isn't working is something you want the HRV to work with not against. Set it up whichever way best facilitates your plan.

Some things to think about.

Dumping cold air on the upper storey of a multi storey home, can increase the thermal stack effect, that is, you will feel a draft as the air drops to lower levels and it will be harder to balance the levels. Dumping it in a lower level and allowing it to work its way up slows down thermal stack.

If there is already force air duct work, it will allow air to move upward through the levels. Does it really make sense to run two systems parallel to each other especially when one is much larger and has much less static pressure? There is no need to run a furnace fan to distribute 250 cfm of fresh air.

Northern states and most of Canada have outdoor winter temps that are too cold to dump into living areas even if preheated by the hrv. Why go with the beauty of draft free radiant heat and then introduce drafts with a hrv? However, as Badger mentions, air moving over radiant floors will soon warm.

Unless you store a large amount of soiled laundry in the laundry room (or use it to store other noxious chemicals) there may not be a need for a return from this room. If laundry is done once a day, enough air is exhausted by the dryer to keep the room sweet. If you have extra exhaust requirements take it from some major closets. Suits that are regular wear items benefit from the airing.

With hrvs that shut down due to cold or frozen conditions, you may not have bathroom exhaust when you need it most. In cold climes control of r.h. is more important especially in the washrooms during showers etc. to prevent heavy condensate on windows. At the same time, it is the high humidity that freezes up the exchanger in the hrv.

with regard to flexible ducts
consider
• what is the increase in static pressure? Many systems are not professionally designed and the static pressure could play a big part in unbalancing the system. Long runs get nothing , short runs get drafts. As well care must be taken not to kink or crush the pipe during install or by other trades later.
• a simple kitchen fire that would normally be contained by the drywall, now jumps into the joist space and ignites the dust there. For the cost of a few lengths of steel pipe, the house is lost.

Am building our SW facing energy-efficient home (1850sf+/-) shortly: Reddiform ICF for all outer walls from footings to roof, stuccoed, 3" Dow SM under basement slab, all joints taped, infloor hot water radiant, engineered 20" wood floorjoists which are topchord bearing on LVL ledgers for clearspan basement, with extra horizontal strongbacks to make a truly monocoque floor system, stapleup radiant tubing, 7.5/12 roof trusses 16" o/c with 4' overhang, single attached unheated garage, hardcoated windows = 6.4% of wall area, 2 freestanding see-through gas fireplaces (supplementary heat & esthetics, 1 per floor). Am also considering Solatubes ending in ceiling lightboxes to provide indirect mainfloor daylight. All windows are inset are much as possible, with window openings chamfered about 40 degrees. All plywood sheating is glued & screwed, and we will be using an HRV with ECM motor.

Here, in Ontario, Canada, code requires vented attic insulated to R31, or if not vented, R50 under the roof. This house will be very tight, and I do not want a vented attic; would rather have 5/8" plywood sheathing totally covered by waterproofing, and, under the steel roof with ridgevent, I would like to install vertical 1 x 2 strapping, then horizontal 1 x 3 roof strapping, to have sufficient venting. I'm wondering how best to insulate under/over the roof: 3' or better DOW SM/Roofmate foamboard, sprayfoam, or mineral insulation? I've considered extending the outer housewalls upward by installing plywood kneewalls between each truss, and covering in sprayfoam, which will also seal any very small leaks we may miss.

An HRV installation is mandated by the Ontario Building Code for all new construction; I would really prefer to locate the HRV, centrally to the various duct ends, in the attic, and am also thinking that the kitchen (maybe not!) & the 2 bathroom fans can be replaced by HRV ducts.

Any advice or criticism will be welcomed, and a big "thank you" for not only your professionsal viewpints, but also for the explanation of various acronyms.

Install an exterior vented range hood. The HRV should be OK for bath vents if allowed by codes. Why not use raised heel trusses or raise the side walls, and use blown cellulose for attic insulation? inexpensive and you can install a lot (R-70 or R-80) for a reasonable cost. If you want to insulate on top of the roof, use 10" + of polyiso insulation, strapped with 2x4's fastened through the foam and sheathing into the rafters with 14" screws, then strap or sheath that for the metal finish. Any metal roof should have a way for condensation underneath to run off, so install roofing fabric on top of the 2x4s - the fabric can sag - so the condensation runs down the fabric and off the roof.

would rather have 5/8" plywood sheathing totally covered by waterproofing,

I suggest that such waterproofing is usually a 0 perm vapor barrier too. Vapor barrier on the exterior side in a cold climate - avoid it if you can.

The stack effect works to your advantage when using heat recovery ventilators in cold climates.

We licensed "yes licensed" mechanical contractors here in Minneapolis and use "Energy" recovery ventilators here and in our design practice around the country where cold weather usually means dry outside air. The ERV will recover latent heat going in both directions.

We prefer dedicated duct work and generally exhaust bathrooms and drop fresh air into bedrooms on any level. As with our high velocity air conditioning work terminal placement is a matter of proper design matched with positive experience and factory training.

I have a RenewAire EV 130 in my own remodeled home.

Bob:

First off, I meant to say "viewpoints", not "viewpints".

I will be installing the exterior vented range hood, and HRV bath vents are allowed here. I've been thinking of using blown cellulose; the only problem is how do I pack cellulose right up to the peak, with no voids? I guess the short answer is: hire an insulation contractor, and follow his directions. Alternately, I have a good supply of used 3" DOW SM, and, at R5/inch, 10" would give me the roofing insulation minimum of R50. I don't know, at this point, if less SM on the outside can be supplemented by Roxul, for instance, on the underside, but it will be great fun (not!) installing vapor barrier in the attic. My truss supplier is roughing out a sort of a modified scissor attic truss design, so that may make things easier all around. And yes, I will be installing a water barrier over the whole roof.

Jonr:

I mispoke: it's water drainage barrier over the plywood and under the steel roof, and vapor barrier under the roof.

Badger:

We will be using dedicated duct work with an HRV with ECM motors, timers in each bathroom, condensate drain, & electric resistance coils for defrost; the defrost was not a consideration until this miserable winter weather hit us where it hurts. To balance the system, all supply & return ducts will be of equal length, and the HRV itself will be sitting on the attic floor, or very nearly so. Our site is about 1/2 mile from Lake Ontario, so dry air should not be a problem, I hope. It has been written of multi-storey homes that "Dumping cold air on the upper storey of a multi storey home, can increase the thermal stack effect" and it will be "harder to balance the levels. Dumping it in a lower level and allowing it to work its way up slows down thermal stack." Our home is a bungalow with finished basement, so only 2 levels, but it did make me stop & think. I would be interested in how the stack effect will work to my advantage when using a heat recovery ventilator.

On the matter of dumping fresh air into the heating system return duct, the need for running the blower to move the air depends on the default setting of zone dampers when there is no call for heat or cooling. In my three-zone system, the dampers default to "open." When a zone calls for action, the dampers for the other two close.

Yes I agree that supply ducts in a master bedroom is really very cold and also too much of cold is uncomfortable. So, for the master bedroom I think, split window AC maintenance Manhattan will be very helpful. Still, I would say before installing take the advice of the HVAC contractors, they will suggest better.

You may duct fresh air in and out of a central HVAC system duct dedicated fresh air to the return of the central system while drawing air directly from sources of moisture such as bathrooms and kitchen.

In cold, dry climates such as high arid planes or mountains we will use a dedicated ERV controlling IAQ while radiating the floors for perfect comfort and healthy living.

Where the fresh air comes into the space depends on the architecture and the occupants along with air flow patterns.

Each house is unique so the designer must use experience and manufacturers' guidelines to come up with appropriate solutions.

Lbear:
Can you provide a source for the white poly flex duct shown in your picture posted 11 Jan 2015 please?
Thank You
Kirk.

The white poly flex duct is from Zehnder. http://zehnderamerica.com/

Very nice duct system--installers seem to like it a lot after they learn how to use it. Kind of expensive.

The duct itself has safety approvals in Europe but not the US; some building inspectors find that an issue.