heat loss from the use of bathroom fans is negligible

I was just remarking that if the heat loss is negligible, then why is using an hrv in a bathroom a better option than a regular exhaust fan (besides pressure equalization, which can be solved without an hrv unit by wiring the furnace to intake air while using the exhaust fans)?

Posted By nolanarcher on 16 Sep 2010 02:04 PM 

can be solved without an hrv unit by wiring the furnace to intake air while using the exhaust fans)?

Yes you could do that, but the HRV does more than just equalize air. It conditions the cold air coming in thru a core and gets it closer to the interior temperature. Your airhandler also draws more amps than the HRV too.

Also, because it's on 24/7 it will get all the humidity and odors out of the bath & keep it fresh. Plus, since it is a central system it is essentially silent.

Yes, I understand the theoretical benefits of an HRV. But if the designer is saying you have to have regular exhaust fans in addition to your HRV, to handle the moisture in the bathrooms... Then your HRV is not getting all the humidity and odors out of the bath, the exhaust fans are. And the exhaust fans do not condition the cold air coming in, because all of the heat in the air that they've just released has been lost.

Great timing for this discussion! I'm about three weeks away from framing on a 3200sqft new construction project. I'm also going with a RecoupAerator ERV. I am going with dedicated stale air ducts from two bathrooms and perhaps the kitchen, and a fresh air supply directly into the HVAC ductwork. I plan to use smaller ducting to the kitchen so most of the draw will be from the two bathrooms. UltimateAir sells booster wall switches which will temporarily run the RecoupAerator at its 200cfm maximum for 20, 40 or 60 minutes. I'm trying to decide if the resulting airflow will be enough for me to skip the bathroom vent fans, or if I should include them as a backup.

The master bathroom is 11' x 16', and has a shower, soaking tub, and toilet. The HVI rules put this at 150cfm of ventilation, which seems quite high to me. I wonder if I should track down the appropriate code official and discuss this topic with them?

I also plan to call UltimateAir to discuss with them too. I'll report back!

More so than HRVs, ERVs need balanced air flow on both sides to work properly. http://www.advancedenergy.org/buildings/knowledge_library/ventilation/erv.pdf For a complex design, you'd want an installer who can do the math.

Todd, that's quite an interesting article. It warns against installing ERV stale air exhaust ducts in bathrooms because moisture gets transferred over to the fresh air intake into the house. It specifically mentions a wall-mounted control in bathrooms which boosts the unit's operation, just as I've been considering. The RecoupAerator manual suggests bathrooms and kitchens as optimal exhaust duct locations. I live in the Northeast rather than the Southeast, so I'm not sure how much this would apply to my installation. But at the very least, it alerts me to this issue so I can consider it further. Thank you!

I spoke to UltimateAir about the RecoupAerator today.  Here is what I learned.

Q1. What happens if I run a bathroom fan or electric dryer, will the RecoupAerator serve as an intake path to bring in MORE fresh air beyond what the balanced flow requires?
A1. Due to the way the airflow thorugh filter media works, additional intake air will not be able to freely enter the home through the RecoupAerator.

Q2. Can this be used as a replacement for bathroom fans?
A2. Yes.

Q3. My bathrooms are 65' apart.  If the RecoupAerator is 10' from one bathroom and 55' from another, how important is the duct balancing?
A3: The HVAC contractor will need to size the ductwork accordingly.  For example, the short run may use 4" ducting and the long duct may use 8" ducting.  He will have the software necessary to do this.

Q4. I see that you have wall controls to temporarily boost airflow.  Can multiple boosters be tied together?
A4. Yes, the remote boost controllers are simply relays that short two lines together.  Multiple relays in parallel can perform this task with no harm.

Q5. The manual mentions that the EconoCool is optional.  Do I need to buy this separately?
A5. This functionality is included, it's simply optional to use.


However, at the following link:

RecoupAerator Installation FAQ

it says:

Should I use the RecoupAerator to ventilate my bathroom or kitchen?

The RecoupAerator is a balanced forced air mechanical ventilation system. It is programmed from the factory to bring in the same amount of air that it takes out. Appliances such as bathroom exhaust fans, kitchen exhaust fans, and dryers only remove air from the home, having little to no effect on the airflow or performance of the RecoupAerator. In some instances, mechanical ventilators have been used to replace kitchen and/or bathroom fans. The drawback to this is that restricting the ducting design, which is necessary to remove stale air from bathrooms and kitchens specifically, will decrease the overall ventilation performance. The RecoupAerator’s main purpose is continuous ventilation for the benefit of the occupants and to maintain indoor conditions that increase the life of the home structure. By designing around the bathroom and kitchen, the overall movement of air throughout the home could be compromised. Replacing kitchen and bath fans with the RecoupAerator is not recommended, but has been done.

I think I am going to install three intakes - two bathrooms and the kitchen - and still install traditional bathroom fans.  If the ERV provides enough airflow that I don't need the bathroom fans, that's great.  But if the ERV alone isn't sufficient in some cases, I'll have the bathroom fans as a backup.

A couple of observations. First one is safety -- here are some pictures of what happens when Venmar made units fail http://nlcpr.com/VenmarWarning.php I don't have experience with other brands, but it seems reasonable that something installed in a ventilation system should not contain combustible material like plastic cores and fan housings.

The air flow from a Venmar Constructo with 6" ducts is about 225 m3/hr which is then spread across several inlets in the home. There is no way that they will manage to keep shower steam from filling up the bathroom and condensing on the walls, soaking your mirrors, even if the duct is two feet from the shower stall. I can tell you that from experience. If you want to vent a bathroom properly, use a dedicated fan and install an additional back draft stopper in the attic if you have a cold draft coming in when the winds are high and erratic.

Many homes have bathroom fans that are seldom used because of noise. You can get really quiet ones -- I had one once from Panasonic that was amazing quiet and powerful. I am sure there are many more -- but they probably aren't at your home improvement warehouse.

There are bathroom controls for HRV units, but in many cases they are useless. If the unit is off, the control will put it on high speed -- but most of the time, the units are on anyway so pushing the button will do nothing additional. Even it the unit was off, it is rather inefficient to start ventilation the entire house just to activate a single vent. There are probably some expensive systems that can vary the flow rate to a single vent on demand -- but it would seem that a simple bathroom fan would be a lot more effective and probably cheaper.

If you measure C02 levels and use on demand ventilation in a home, you will find that extra mechanical ventilation is almost never needed when it is windy outside. Overall, these things are only needed about 25% of the time from my experience -- and there is no way the humidity based controls can figure out when it is needed. I set mine to 700 ppm for CO2 and many days, it is never on and there are zero odors in the house. 400 ppm is the outdoor level for CO2, and at about 1000 ppm it starts feeling stuffy.

I believe any large odor or moisture source (stove, shower stall) should have a direct vent to the outside, and that HRV systems be used only to supplement the natural air infiltration to maintain indoor air quality.

We've been living in the house for six months now. I installed only the UltimateAir RecoupAerator ERV as the bathroom fan system, with no conventional bathroom fans. There are stale air intakes in the master bathroom, guest bathroom, and powder room. The single dedicated fresh air supply is downstairs in the kitchen, which means that there is a reasonably large circulation path through the house.

The ERV is set to run at a low level all the time. The "always-on" speed is controlled by the knob on the ERV's wall plate control. Each bathroom has a booster timer (sold by UltimateAir) that temporarily boosts the ERV level to full-high. When the timer expires, the ERV goes back to the speed set by the ERV wall control.

So far it's been working great. Since the ERV stale air intakes are in the bathrooms and run all the time, they are kept nice and fresh. (We've really come to appreciate that aspect!) The RecoupAerator is mounted in the attic, hanging from the roof framing using UltimateAir's suspension kit. Thanks to the isolator bushings, operation is silent at partial levels, and barely noticeable in the room directly below at the boosted level.

The master bathroom is large and we have no condensation issues. The guest bathroom is a smaller room. It will start up build up some fog on the mirror during longer showers, but it clears quickly since the ERV continues to run on low even after the timer expires.

Having the ERV in general has been great. We have an additional timer switch by the kitchen, and it does a great job clearing the house of cooking odors. It also keeps diaper/dog odors from building up.

And, something I never initially considered - the ERV had a substantial positive effect on reducing the radon level in our house. Our house tested high for radon. I bought an electronic radon meter to measure the level. The house tested at 35pCi/L in the living space with the ERV off, and at 20pCi/L with the ERV on. We've since sealed the slab and installed a radon fan, and the level is down to 0.7pCi/L.

Overall, I feel more comfortable knowing we are getting constant air exchange in our living space. Please feel free to ask questions.

 - Chris

The Renew Aire ERV we use in our work - and I have in my home here in Minneapolis - is self balancing within limits. An ERV is a must in tight homes as a regular bath exhaust will quickly pull a negative and does not control the infiltration of hot or cold "unconditioned" air. In mixed weather climates the ERV excels.

The guest bathroom is a smaller room. It will start up build up some fog on the mirror...

So, that occurs even with attentive use of the booster timer during showers?
It looks like your system has three stale air intakes. Is the intake air balanced between them such that about 1/3 of the RecoupAerator capacity is drawn from each?