We are in the midst of building a home with Polysteel ICF basement walls and Enercept SIP's on the main floor.  We will be installing a Venmar ERV unit, but was wondering if that is enough in the bathroom areas?  Will it keep the steam out of the room or will an exhaust fan be needed?

If  you do use an exhaust fan, what is the common practice when working in tight homes?  Will these areas be a heat escape route?

Thanks for the help,
Ben

The manual from Venmar says, "In every case, bathroom fans and a range hood should be used to exhaust stale air. Also, for homes with more than one level, we recommend one exhaust register at the highest level."  On balancing it says, "Turn off all exhaust devices such as range hood, dryer and bathroom fans."

 

It looks like Venmar is expecting there to be both bathroom and kitchen exhaust devices. 

 

In our area it is a code requirement to have so much exhaust from the bathroom based on the room size.  Consult the local code that you are under or talk to the building inspector to see what they are going to require. 

Thanks. We are dealing with a very reputable HVAC dealer and they are not recommending exhaust fans. There is not a code in Iowa that defines exhaust fan size, at least in our area, there is not. I just want to make sure I will not have steam in the bathrooms and exhaust fans seem to be the only way to achieve this.

Typical code requires "no window, install an exhaust fan".

When there is a window, no one opens it anyway, so I always install exhaust fans, always!

In Logan, Utah area, we built a house with 4 bathrooms, 2 on line, and 2 in the basement not finished yet. We are using a HRV to maintain SOME air flow all the time, and the HRV sucks thru the bathroom fans, so if we turn on the fans, you get even more ventilatlion. Ours is a dry climate, and we get a little steam during a long shower, but it clears out in minutes once the shower is turned off. I would install fans in series with the HRV in any new installation, it gives you more ventilation than you need, but more is better than not enough. Those fans are cheap anyway. The HRV is expensive, but nice to have in a well sealed home.

So what you did was run the exhaust fans into the ERV outlet, and triggered the fan and the ERV to come on together.  That seems like a great idea.

Does it create a problem when the exhaust fan will operate at higher cfm than the ERV?  You most likely will be pushing more air out than the ERV normally handles.  Will you get moisture buildup in that exhaust line, or nothing to worry about?

not exactly, the fans are electrically independent of the HRV. I run the HRV in the winter months all the time, on low speed ( 1 of 4) and in the summer I set the speed at 2, but only run it when I feel it is needed, such as during a shower or using the toilet. I use a handheld RF remote switch like the ones used in ceiling fans. Summers are mild here and the windows are open a lot, definitely from evening to mid morning. With the HRV running or not, the bathroom fans are a backup or stand alone option. It appears that running one fan into a 4 into 1 plenum that takes in several bathrooms before going to the HRV would send moist air from one bathroom to the other, but each exhasut fan has a small damper in its exhaust that cuts down on reverse flow. I didn't think this up on purpose. The local building inspector didn't know what a HRV/ERV is and made me install the fans, so I just ducted them to the HRV instead of to the outside.

The HRV has a condensate drain, and our first winter here it actually produced some water in the bucket I had under it, but not much. Walmart has some small temperature and humidity monitors for a cheap price, I hung several of those in the house, and the humidity never exceeded 30%, even when I vented our electric clothes dryer into the basement to reclaim the heat. If you do that, use a really good bag filter. On 3 levels, we have 4500 sq. ft, and a load of laundry barely increases the humidity. It is so dry here in northern Utah that our gas furnace has a humidifier, but we only run that in the winter months.

We are considering an ERV system for our house in southern California were it can drop 20 degrees in the evening for the purpose of healthier indoor air and capturing heat in the winter and cool in the summer.

Our house will be SIP walled. We understand that eight exchanges a day are suggested for healthier interior air. Should we trigger the exchanges only late at night so the Humidity or 20 minute push button timers won’t conflict? What happens if both trigger at the same time (Scheduled on cycle and push timer or humidity sensor) Can an ERV take the place of shower fans, will they pull 100CFM ?

Thanks Guys John

Air exchanges are needed while the house is occupied, for healthy air. As for controls, don't over complicate. Like Engineer Scotty says, the more you overthink (over engineer) the plumbing, the easier it is to stop up the drain....

An ERV or bath ventilation fan is limited by two things; capability of the "appliance" and capability of the ductwork, or diameter and length (esp; external static; HVI ratings always published on certified products). 

Unless the duct run is short, you would need 6" diameter to have a chance at 100cfm, with at least 100cfm bath fan or ERV.   The ERV provides "make-up" air that exhaust only fans do not provide, as well as recovering energy used to cool or heat that exhausting air.   If the ERV is capable of 180cfm, and you are venting three bathrooms, take 180cfm divided by 3 rooms or @ 60cfm per bathroom, if balanced equally.   Because the ERV is operating to achieve 8 air changes per day (as a maximum starting point), you have much more ventilation than 100cfm running 15 minutes a couple times a day.   (Many minimum ventilation codes are 50cfm intermittent or 20cfm continuous.)

In a super insulated or SIPs house, an ERV provides balanced ventilation (when venting bathrooms and the general kitchen area, not the range hood) instead of turning the house into a vacuum pump with all the exhausting fans.   Unless the bath ventilation fans have positively sealing back draft dampers (most don't), non-operating fans provide unintentional make-up.  Closed combustion (two pipe or concentric) heating and water heating are a must in these homes as well.   

Been in my 2500sf SIP home for two years now.  I am in the Sacramento area and I do not use a recovery unit. 

I have a 4" filtered vent line that runs from an outside vent to the air handler inlet line. This gets fresh air inside whenever the air is on.

I then ran all of my bathrooms, utility room, washer room vents into one 8" duct that is powered by one 8" inline fan that runs at a maximum of 800cfm.   It exits through the roof via a single vent. Each room has an adjustable, dampened inlet vent and a timer switch (5-30min) that can turn it on.  I then have a master switch in the master bath that has the ability to be programmed to come on/off at anytime throughout the day/night.   Or it can be switched on as a poormans wholehouse fan.  It works great and is very quiet and inexpensive vs individual fans for each bathroom.  My HVAC guy was sceptical, but it works great.  I realize that it pulls more air into the house than a standard 125cfm bath fan, but if you were to use it with a recovery system you could gain the benefits of both.   I always hated the noise of a conventional bath fan, having to clean the lint/powder from them, vent them each.  My design has worked well for me.

I like to use the HRV as the bathroom fan. HRV's/ERV's should exhaust from the bath and kitchen and maybe even the basement and laundry room anyway, why not use them for both. The unit I use is a fantech (no affiliation) unit that has very nice controls. While the controls allow for you to set the fan speed and control the time the unit remains on, it also allows for boost switches to be added. I simple place a 20/40/60 min boost switch in the bathroom to allow for control in the room. MA does require ventilation in the bathrooms and it needs to be controlled from within the rrom. Here is one issue I have with the exhaust only type of fans. If you have a very tight house, you will create negative pressure in the home and even backdraft some appliances, like dryer and stove hood. While these typically have back draft dampers, if they are used in conjunction with the bathroom fan they will not provide the needed ventilation. Once again this is in a tight home. One SIP's house I recently visited had exhaust only ventilation in the bathrooms, stove hood, and a wood stove, with no means of making up the air being exhausted. This presented a problem with all of these appliances. I tested the air flow coming from the bathroom fan and it didn't vent the amount it was rated for. They have also experienced problems with the wood stove and can't even get it to light if the dryer is running. Balanced ventilation is the way to go IMHO, maintaining a slightly possitive pressure inside to stop unwanted heat/cold/humidity from entering your home.

Tom Pittsley
[email protected]
www.eebt.org