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Need consultant expert on residential ERV/HRV air balancing

I live in northern VA suburbs. My residential HVAC system includes a LifeBreath ERV, which has been installed for 5 yrs. During that time, I have had contracts with 3 different HVAC service companies. NONE of them have been able to keep my ERV exhaust & intake air flows balanced. In the DC metro area, is there someone who is expert on RESIDENTIAL ERV/HRV installation & air flow balancing whom I can hire as a consultant to (1) diagnose cause of my ERV air flow balancing problem, (2) recommend solutions, (3) provide on-going ERV maintenance, or if not, at least teach myself and my HVAC contractor how to balance the ERV air flows? Please provide advice, contact info, etc.

On a related matter, I have found that even with a "whole-house dehumidifier system" , in this climate region, it is impossible to operate a residential fresh air ventilation system DURING THE HOT HUMID MONTHS, without the house interior humidity being raised over 50% and frequently over 60%. To date, in hot humid weather, we have had to shut off the ERV system in order to keep interior humidity levels below 50% even with a whole house dehumidifier system in operation.

Asked by Terry Sopher Sr
Posted May 14, 2014 5:09 PM ET
Edited May 14, 2014 5:14 PM ET


8 Answers

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Your post raises several issues. I agree with you that a site visit by an experienced consultant would probably be helpful.

1. I'm not sure why you think that your ERV is unbalanced.

2. Any ventilation during hot, humid weather increases the latent load that an air conditioner or dehumidifier has to handle. If you are struggling to keep your indoor humidity levels where you want them, it's possible that (a) you are overventilating, or (b) your dehumidifier is undersized.

If you are willing to throw money at the problem, it's always possible to buy a large commercial dehumidifier to handle almost any latent load. But it's usually smarter to solve this type of problem by reducing your ventilation rate during hot, humid weather.

Answered by Martin Holladay
Posted May 14, 2014 5:23 PM ET
Edited May 14, 2014 5:30 PM ET.


Martin, thanks v much for quick response. FYI further info for your consideration.
1. (a) This failure to stay balanced over time is confirmed by HVAC tech doing repeated air flow balancing measurements [using digital electronic air pressure manometer; NOT pitot tubes] at subsequent days after initial balancing. I am told by my HVAC techs that pitot tubes are NOT necessary to do air balancing; Airia tech staff insist that only pitot tubes will enable air balancing. RESPONSE?
1. (b) Manufacturer [Airia] advises balancing with ERV & HVAC air handler fans on "high" setting. When we do that, the air flows are NOT balanced at lower fan speeds [confirmed by HVAC techs doing air flow measurements at lower fan speeds after having achieved balancing at recommended highest fan speeds]. IS IT EVEN POSSIBLE TO GET ANY ERV/HRV BALANCED FOR VARIABLE FAN SPEEDS? OR DOES ONE HAVE TO ALWAYS OPERATE ERV/HRV AT "HIGH" FAN SPEED?
1. (c) Also, the most recent time that the air flow was balanced [at highest ERV & HVAC fan speeds], air flow balance was able to be achieved ONLY by having ERV intake fresh air damper FULLY OPEN, and ERV EXHAUST AIR DUCT DAMPER ALMOST FULLY CLOSED! That was the only way to get air flow balancing even at the AIRIA-recommended "high" fan settings for ERV & HVAC air handler. If the HVAC air handler and/or ERV fan speed is set to a lower speed than "high", there is negative air pressure in the house apparently.
2. Yes, I see it's possible that I'm "overventilating" if ERV fan is at "high" speed in order to maintain air balance. Dehumidifier system is <1 yr old Honeywell DR90, which 2 different HVAC techs told me was max that should be installed for my 3 ton heat pump system [also told 3 ton heat pump system was proper size for my house]. Yes, I understand your excellent point that reducing ventilation rate in hot, humid weather is wise approach.

Answered by Terry Sopher Sr
Posted May 14, 2014 6:05 PM ET


I'll take your word for it that your ERV system isn't perfectly balanced at all speeds. However, you may be overthinking the issue of whether this matters.

Most houses with ERVs will fail to be perfectly balanced, because appliances like clothes dryers and range hood fans operate intermittently in a way that increases exhaust air flow from the house. Frankly, even if your ERV isn't perfectly balanced, it's still providing ventilation. So perhaps you should stop worrying about perfect balance.

Second, if you are operating your ERV continuously at high speed, you are probably overventilating. Do you know your ventilation rate in cfm? Have you tried to match your ventilation rate to ASHRAE 62.2 recommendations?

Remember, it's always possible to control an ERV with a timer, so that it operates (for example) for 15 or 20 minutes every hour.

Answered by Martin Holladay
Posted May 14, 2014 6:41 PM ET


Is the ERV connected to the ductwork for the HVAC system?

Answered by David Meiland
Posted May 14, 2014 8:33 PM ET


What's a "digital electronic air pressure manometer"? Pitot tubes are often connected with electronic manometers. If the techs used manometers to read airflow, what device did they connect to the manometer? Where did they take the readings, interior registers or exterior?


In general I like to follow manufacturer's directions, and I don't have much experience with ERV's. But it makes intuitive sense that you would measure airflow at the exterior of the house on both the exhaust and intake. Generally a flow hood is a lot easier to use than a pitot tube, and I would be surprised if the manufacturer didn't allow you to use one.

It's definitely possible (likely) to get balanced flow across varying fan speeds. The fact that you're not getting this makes me think that you're either not accounting for major duct leakage somewhere before your reading location, or that you're using inaccurate measurement devices/protocols.

Consider looking for an HVAC tech with a NATE Air Distribution Service certification in your area.


Answered by Jesse Smith
Posted May 15, 2014 8:00 AM ET


It sounds like your ERV is connected to a variable speed heat pump air handler? If so, then you would have a hard time getting balanced flow on your ERV in all scenarios.

For a NOVA consultant, who can probably help you with these issues, try http://www.conwaygreenconstruction.com/

Answered by John Semmelhack
Posted May 15, 2014 8:13 AM ET


Thanks all for responses. FYI: House is 60 yrs old split foyer approx 1800 sq feet living spaces. New windows & doors with little air leakage; attic air-sealed to pretty good level; R-50 attic insulation.

FYI: ERV operates off digital timer; usually set to ventilate 20 minutes out of every hr. Exception = in hot, humid weather, when we operate it only intermittently to avoid house interior humidity >55%.

Yes, ERV is connected to the HVAC system ductwork: ERV exhaust air pulled from 1 of 2 HVAC main return air ducts; ERV "fresh outside air" ducted into HVAC main return air duct with recommended 6' minimum separation between ERV exhaust duct location & ERV fresh air duct location on HVAC return air ducts.

Yes, ERV is connected to common modern-day "variable speed" air handler for my heat pump system.

Re ASHRAE 62.2 standard: am I wrong that this standard is only a "comfort" standard, & NOT a standard based on indoor air quality considerations in light of indoor air chemical loads from furnishings, etc.? My personal view FWIW: given high levels of chemicals in typical house furnishings, finishes, & construction materials [even in some "green"/LEED homes], the ASHRAE recommendations for air changes/hr or /day are inadequate to provide high quality indoor air not contaminated by chemicals out-gassing from said furnishings, finishes, etc. Let alone considerations of individual medical conditions such as whether residents have respiratory disease that makes their lungs reactive to low levels of indoor air chemical contaminants.

Re over-concern with "balanced" ventilation air flow: perhaps. But isn't some level of concern appropriate given potential condensation/mold problems in certain climates/house envelope if one has excessive positive pressure, or potential for pulling in outside contaminants or moisture under negative interior air pressure?

Again, my deep appreciation to all for thoughts & advice, and John S. thanks very much for the referral to NOVA consultant; and Jesse for NATE referral.

Answered by Terry Sopher Sr
Posted May 15, 2014 4:13 PM ET
Edited May 15, 2014 4:15 PM ET.


It sounds like you care more about having high quality ventilation than the average homeowner. If that's so, you should know that your ventilation system isn't optimal. The best ERV and HRV systems use dedicated ventilation ductwork; they don't try to patch into existing forced air ductwork. There are several reasons for this, but you have apparently encountered one of the reasons: the blower on the air handler makes it hard to regulate the ERV airflow and balance the system.

If you are willing to invest money to fix this problem, you can hire a ventilation contractor to install dedicated ventilation ductwork.

Q. "Am I wrong that this ASHRAE standard is only a comfort standard, & NOT a standard based on indoor air quality considerations in light of indoor air chemical loads from furnishings, etc.?"

A. Yes, you are wrong. The ASHRAE standard is not based on comfort. The ASHRAE 62.2 standard states, "This standard defines the roles of and minimum requirements for mechanical and natural ventilation systems and the building envelope intended to provide acceptable indoor air quality in low-rise residential buildings. ... This standard applies to spaces intended for human occupancy within single-family houses and multifamily structures of three stories or fewer above grade, including manufactured and modular houses. ... This standard considers chemical, physical and biological contaminants that can affect air quality. Thermal comfort requirements are not included in this standard."

Answered by Martin Holladay
Posted May 16, 2014 6:24 AM ET

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