New three story ICF construction / Andersen Series A windows, blown insulated attic in coastal area of Delaware. (No basement) Geothermal HVAC - Two independent ducted zones Zone 1: Ground Floor + 1st Floor (total square foot = 2,400) Zone 2: 2nd (top) Floor (total square foot = 3,000) Floors are connected by 4 foot stairwell "tower" with landings on each floor. This is a very tight house and needs ventilation. Builder forgot to install ERV (in spec) until after home was 99% complete, drywall, trim, paint, etc. Builder/HVAC contractor who installed the Water Furnaces need to retrofit ERV into the home and are recommending that a single ERV be installed and tied into the Zone 1 only. Room Air from ERV would be tied to Return of furnace. Fresh Air from ERV would tied to Supply of furnace. They say the ERV blower may be operated separate from the Furnace Blower. 1) Will one ERV be sufficient to provide adequate air exchange to 2nd floor? They tell me there will be sufficient "mixing" of fresh air via the single stairwell. 2) I've read that it's best to have completely separate ducted ERV system from HVAC, but since this would not be costly, the builder/contractor are recommending to use existing duct. Is this a valid design? The design recommended is documented n the RenewAire Installation and Operation Manual for Models EV70, 130, 200, 300 in schematic "D" - title: "Furnace Return Air Into Furnace Supply Air". Thanks in advance for any input on this issue.

They say the ERV blower may be operated separate from the Furnace Blower.

What they didn't explain is that if you do, then the ERV will be unbalanced and pressurize or depressurize the house - it works, but is not good for in/ex filtration. Unless you have an ERV like the Reversomatic (self balancing flows - over some range of pressures).

Schematic D also suffers from a short-circuit path through the furnace (when the furnace blower is off). And ERV flow might stop (when the furnace blower is on).


How well ventilation is working is easy to check with a CO2 meter. I can clearly see the difference when a window is open vs all ventilation off (you need to sit there and breath for awhile).

-in/ex filtration is a moot point with an ICF home. One - it is virtually air tight. Two - even if unbalance could push moisture into the exterior walls, there is nothing there that can get damaged, certainly not the foam or concrete.

With a three storey house there will be considerable thermal stack effect. At times you will be able to feel the air currents in the stair well. One portion will feel cooler as the coolest air from the third storey floor spills down the stairwell and one portion will fell warmer as the warmer air of the two lower floors rise to the top. So yes you will get mixing between floors. Will it get the fresh air right where you want it? Maybe, maybe not. Depends on a number of factors. Do you have individual exhaust fans in bathrooms etc.? Where do the ducted zones start out? Are they both on the lower floor or is the second zone totally in the third floor? Is the top floor bedrooms? Is it all cut up with small rooms or is it a big open space?

For more then thirty years over 80% of new homes build in Canada have used the fresh air into the furnace duct system. In the last two Code revisions, additional exhaust capacities (principal exhaust) are required in some circumstances but the incoming air is still usually brought in by the furnace system.

It doesn't mean that using the furnace to redistribute the fresh air in is the right way to do it even if the building code says it's OK! The building code is directed at tract builders who try to build homes as cheaply as possible for the most profit.
A completely separate ducting system is the right way! fresh air into the bedrooms stale air out from the bathrooms, kitchen and laundry room, timer switches in the rooms with exhaust vents, more expensive but a much healthier environment!

John

The really right way is a separate fresh air supply AND return in any room where the door will be kept closed when people are in there.

In/ex filtration causes more ACH that aren't flowing through the ERV - an energy negative in any home, even if you don't care about dripping condensation on your drywall. And all homes have leakage.

Well, Johny, you are not exactly correct. The building Code is directed at anyone who builds a structure that is covered by that code. It does not matter if it is a diy or a tract builder, if it is an outhouse or a castle, the code applies. But yes, it is the minimum requirement.
But please consider, HRV's in residential buildings pretty much came into existence to support the Canadian R2000 program back in the eighties. After a decade of following the data, the researcher in Ottawa came to the conclusion the HRV's where not necessarily the best way to maintain indoor air quality. At that time they move to simple exhaust units and make up and combustion air to the furnace. Research and the Code still maintain this to be the case when a building is equipped with a forced air heating system. The bit of energy saved by HRV's in recovery is offset by the power the units consume and the fact that in cold climates, the either have to shut down, recycle indoor air or add electric heat to defrost the cores. You cannot run warm moist air past cold air without the condensate freezing up. Yes, some of the new models have decrease this deficit. This does not mean the furnace should not be used to bring in fresh air on its own. And it does not mean fresh air dumped into the furnace will not be suitably distributed throughout the house, especially in a three storey building as posed by the OP.
Consider that Canadians spent more days hibernating in their homes then most other areas of North America and during these times the windows are seldom open, so we take our indoor air quality very seriously. It is unlikely that any other jurisdiction on this earth spends more time and money on fresh air concerns then the boys in Ottawa.

But hey, if you are still not a believer, try this. Take a three storey house heated with forced air. Shut of all air movers and close all doors and windows. Go up to the third floor and pull a floor register. Wrap a thin plastic bag around it so that the plastic is just around the flanges and reinsert it. Close the door to the room and watch the bag inflate, or deflate. I say deflate because depending on the duct layout and design, ghost flows often reverse from the mechanical flows. What you are witnessing is often referred to as a thermal stack effect. Warm air rises as the heavier air settles lower. Much of this thermal effect will occur through open stairwells but some also occurs through the air plenums and duct work. As long as there is a supply and return in the room, air will mix. You simply cannot stop it. In OP's case, if the second air handler is also on the lowest floor, there is no question that it will set up convection currents with in the duct work. There is also no question that the stairwell will also mix air between floors unless each level is sealed with an exterior grade door.

Still not a believer? Try this. Take the same three storey building, under the same circumstances, park your easy chair in any room that has a supply and return air, close the door, relax in the chair and start a stop watch. Now light up a good cigar and then tell me exactly how long it takes before Granny is banging on the door asking why your are stinking up the WHOLE house.

Just because one building "scientist" offers an opinion that a completely separate HRV system is the best and 100 people on this forum repeat it, doesn't make it fact. It remains just an opinion and it means we have 100 gossip on this forum ;-) Most of who have no idea who started the rumour! They just thought it sounded good.

If you do not have a forced air system in the house, then yes you need to rethink everything!

Jonr - I believe that if you take the time to think about it, you will agree that the foam behind the drywall in an ICF home will keep the drywall at room temperature, therefore no condensate, no dripping. And you missed the point about limited in/X so there will be hardly any AC's that are not going through the ERV.

If you take you average H/Erv of 75 to 150 cfm and distribute it over all those rooms, you will wind up with 10 to 20 cfm's per room. Now the average room with forced air heating will have return air grilles of about 8" x 10". These will feed into a joist space plenum of about 9" x 16" which in turn connect to the return air duct of probably about 18" x 20". This duct in turn communicates with the return air in the adjacent room and with the rest of the heating system. Even if all doors are closed, I believe this would suffice as a sufficient relief venting for that 10 to 20 cfm's introduced by the HRV, right? No unbalance, no return needed to the HRV.

Due to thermal stack, all houses are unbalanced up and down, the more storeys, the more unbalanced. Any available leakage will cause unbalance side to side on a windy day, the more wind, the more unbalance.

The RenewAire OP cites has two blowers. It will have balanced flows in and out as much as the house will let it. If there is another exhaust fan or vacuum running, it will not be able to put out quite as much air as it takes in. Wether it is dumping to its own duct system or into the forced air system makes little difference. As a matter of fact, because dumping into the force air system produce less restriction and or turbulence than forcing the ERV to blow and suck through 50 or so feet of its own duct and hoping the static pressure is identical on each, from an over all house to outside balance, it is far better to dump into the FA system.

It is unlikely that schematic "d" will cause enough bypass to worry about due to the volume of air in the ductwork and plenums of the furnace compared to the volume being introduced by the ERV. There will always be some air flow through the ducts blending the air. If there is a reverse ghost flow, the volume of bypass air would increase slightly.

I do live in Canada, I do live in Ottawa, and I have built two custom homes. The latest is an ICF home, a bungalow, ICF walls from the footings to the eaves, walkout basement. two inches of foam in the attic before topping it off with cellulose.

The house is so airtight that the front door lock freezes up in February on occasion, our coldest month, the HRV runs 24/7 the furnace not so much. I need to have the fresh air distributed in a guaranteed method not by a furnace that may come on or not.

Every house needs to be analyzed by a competent person who is familiar with the the way the house is being built, how well it is assembled. Many of the homes today leak air but they can also leak in many different ways, just poor building practices by the lowest bidder.

I do not have any registers heating or cooling the basement they are all closed so there is some leakage, it is not finished at this time. The temperature difference in the winter or summer varies between 2 or 3 degrees Fahrenheit mostly due to the foam under the concrete basement floor.

I have had a two story house, double wall passive solar with the stack method in the stairwell utilized for heating. this was thirty years ago and the method of the HRV fresh air connected to the cold air return of the forced air in the basement. That was a BIG mistake it cooled off the basement in the winter and the only thing possible was to add supplemental heating when we wanted to use the basement.

Relying on the forced air furnace to circulate the fresh air in a well built (sealed) house won't happen. It needs a separate system for the HRV and another for the forced air to ensure clean fresh air for all occupants.

The house is so airtight that the front door lock freezes up in February on occasion

Ex-filtration in Winter is a bad thing (I purposely run very slightly negative and I disabled the humidifier that came with the house). On the other hand, if it's 90F and 95% RH outside, you really don't want any in-filtration.

Johny - I was not trying to suggest that a center stair well should be used for heating/ventilation, only that thermal stack doses occur in these stairwells. It is not a good way to heat but as it happens and you can't stop it, it can be considered when planning fresh air movement in a house.

"Every house needs to be analyzed by a competent person who is familiar with the way the house is being built, how well it is assembled."
I totally agree. That is why I take exception to statements like "A completely separate ducting system is the right way!" or "AND return in any room". Some times these apply, sometime they don't.

"I have had a two story house, double wall passive solar with the stack method in the stairwell utilized for heating. this was thirty years ago and the method of the HRV fresh air connected to the cold air return of the forced air in the basement. That was a BIG mistake it cooled off the basement in the winter and the only thing possible was to add supplemental heating when we wanted to use the basement."

Was it actually an HRV or was it simply incoming fresh air to the return air of the furnace? As you said Every house is different so I can't say for sure what happened in that house. However, I would think that the three storey thermal drift with solar heating the upper two floors would have much more to do with the cold basement then the HRV. The solar heat would have stratified the air in the upper floors forcing the heavier air to drop to the basement. As the upper floors where warm enough, the 'stat wold not activate the furnace and there would be little heating in the basement. Open stair welled multi storey buildings are almost impossible to heat evenly.

I would be very interested to know what the size of your new house is and what the size of the furnace is.

"The house is so airtight that the front door lock freezes up in February"

This brings us to jonr's concerns. A very valid concern, just not in the absolute as stated.
This is one of the reasons the Canadian Code calls for principal exhaust as the way to bring in fresh air. As jonr indicates, it will tend to keep a slight negative pressure in the house preventing the warm moist air from moving into the keyway. This is actually what started the HRV's being used in the R2000 homes. Too many occupants where being locked out of the homes. In your case, it might be that you have an "unbalance" due to some additional air being pulled into the house but I suspect it is just the pressure of the thermal stack. Next time it happens, (and may that be many months away) try the lock on the basement walkout. I suspect it will not be frozen due to "incoming" air as the basement will have the negative pressure of the thermal stack.
As your house is ICF, there is no danger to the walls, however I'm sure you can understand that if it were stick build, the additional pressure on the main floor would force warm moist air in the wall cavity where it would condense and freeze against the back side of the sheathing. Again, this is why the Code is all about vapour barriers to stop this moisture. In the overall scope of things in our climate, it works quite well, but it can produce some problems of its own. Even in high humidity scenarios with air conditionings on, a pressure differential will not get passed the vapour (air) barrier, no move of air through the wall system so no rot problem. Except that wall assemblies using wood will never stay air tight! As they age, the movement of the wood due to thermal and moisture differences will eventually break the vapour barrier somewhere (everywhere). Another lesson learned from the R2000 program.

IAQ is suddenly news in the UK: http://www.myhealthmyhome.com/downloads/Indoor-Air-Quality-Future-Scenarios-Report.pdf (80 percent increase in asthma incidence by 2050.)

But Delaware isn't Britain. Or Canada. Homes are tiny in the UK, about 800 SF. One doubts that a nonsmoking couple in Delaware living in an american sized home really has a problem except to control humidity. Even in England, with families living shoulder to shoulder, the big issue was mold. It's a tough job for two reasons: In a super efficient house hvac doesn't run enough to control it; In wet areas, bathrooms and kitchens, exhaust fans create negative pressure and stealth infiltration in supertight houses. Fireplace? While recovery ventilators could help with the second, tying it into hvac would require air returns in bathrooms and kitchen that aren't there for the obvious reason.

I'd rather have one of these per bath than a single unit: http://www.amazon.com/Panasonic-FV-04VE1-WhisperComfortTM-Ventilation-Patent-Pending/dp/B000XJNZ1Y It would be an easier changeout if regular exhaust fans exist there now. If code requires an erv, I'd run a single exhaust from the kitchen (in an open floor plan) and fresh air vents to the room(s) most occupied. My erv says the exhaust should be 10 feet from the stove.

One doubts that a nonsmoking couple in Delaware living in an american sized home really has a problem...

In a tight new house with no ventilation, I expect that they would have significant problems with non occupancy related pollutants. As the article says:

The main pollutants are particulate matter (PM10, PM2.5, ultrafine particles and fibres), carbon monoxide (CO), excess moisture, nitrogen oxides (NO2), sulphur dioxide (SO2), volatile organic compounds (very volatile, volatile and semi-volatile), formaldehyde, radon, ozone, ammonia and biological particulates (allergens, bacteria, fungi), ".

Most of these change with ACH and the materials used, not people per sq ft.

In an all-electric house, NO2, ozone, CO and SO2 are likely from incomplete combustion outside the home, ie traffic. Hairspray, fingernail polish, chemical cleaners are VOCs, and the latter is also a source of ammonia. A MERV 15 handles most dust. One hopes OP has considered radon, formaldehyde and construction VOCs and taken measures independent of ERV.

Cooking is a major source of indoor pollution. So is excess moisture and the biologic result, which is closely tied to number of showers and loads of wash/day. With the Panasonics and a cure for the kitchen, it's not like there are no air changes. And let's not forget the millions part in parts per million.

Perhaps I assume too much in dashing off all-electric. Here is an LBL study dissing gas cooktops. http://ehp.niehs.nih.gov/wp-content/uploads/122/1/ehp.1306673.pdf Absolutely no reason to spec one. Induction cooktops are just as powerful and responsive. Electric ovens are far superior to the gas kind.

To clarify, I like ervs, run one 10 minutes of each hour. But if OP did not specify separate ducting, it may be very difficult to make a case for it now vs hvac addon if the manufacturer has a protocol for addon, and most do. They want sales. Builders have this tendency to disavow major mistakes. Given that choice, I'd opt for energy efficient dry bathrooms over less effective central, assuming it is less effective. (Depends on tightness and hvac sizing.) Maybe OP should tell his builder he wants a third party contractor whose opinion is not shaded by whose fingerprints he'll find. In choosing, don't assume that any ole hvac contractor can perform well.