I would appreciate advice/input on the selection of ventilation equipment for our owner-built home. I've read/researched the topic (no hands-on experience), but I'm having a hard time pulling it all together - which I NEED to do to keep our schedule moving along. I'm even struggling with the very basic decision of exhaust-only vs balanced (ERV or HRV). From my layman's POV, here are some Specs, Goals and Pros and Cons for our specific situation. I put all this down (a mini-novel for Pete's sake!) to try to show that I'm trying to work out the problem on my own, but I don't know which way to go. Any input or comments are very welcome.
Thanks for your time.

Ventilation Goals:
- Quiet, quiet, quiet operation (check out this GBA blog and especially comments 4 thru 7
- installation price is a moderate factor
- low life time operation is a factor (by that I mean getting hit with a big bill for a new/replacement part/unit and not $2 more for energy bills per month)
- reasonable DIY install is a factor (we feel confident we can install an ERV or HRV & duct it, it is more the design decisions that are a problem for me) 
 
House Specs & Context
- conventional 2x6 framing; zip shtg', owner-applied EcoSeal on framing, air-tight drywall, (mooney wall) with dense pack in walls
- 1,600 sq ft 1st flr (living areas, office, laundry, master bed/bath/closets)
- 600 sq ft 2nd flr (two sm bedrm, sitting area, bath)
- attached unconditioned garage will have 5/8 air-tight drywall
- planning mini-splits for heating/cooling, no duct work
- two occupants full time on first floo, working from home on rural farm (lots of in/out all day long) 
- one to three family visitors on 2nd floor (likely for several weeks stay, not just an overnight)
- location: south-central PA, mixed-humid

Exhaust Only
Description: A good quality, quiet fan in each bathroom with the exterior vent ducted 3' down the wall to help prevent back flow of cold air into the bathroom in winter (I read that idea from Robert Riversong on a GBA thread somewhere). Replacement air would need to "leak" into the house from uncontrolled locations, hopefully not through the attached garage. Crack a window (south side in winter, north side in summer ) when you want fresh air in the living area.

Pros (relative to balanced system)
- DIY friendly in design and install
- easy to operate for the life of the house - even when I'm old and senile ;-) 
- removal of bath moisture at the source with shortest ducting possible just makes sense to me (vs ducting to central ventilator) 
- less possibility of expensive replacement equipment needed in the future when I'm on a smaller income
- since we're planning mini splits for heat/cool, there would need to be NO duct work whatsoever in the house

Cons (relative to balanced system)
- Energy penalty would mean higher energy costs, not sure how much higher and I own a sweater ;-)
- Would negative air pressure in house during several months of AC season lead to moisture/mold problems inside walls? That is a real concern for me. 
- No on-going filtration of interior air (like a HEPA filter) for pollen. That's a problem for my husband's  allergies and mild asthma. What could I do to fix that problem in this design?
- Would the several visitors sleeping in the two small bedrooms and sitting area upstairs (600 sq ft) find it just too stuffy to be comfortable?
- While this set up deals with the two full baths, there is a 1/2 bath on 1st floor that does not have an exterior wall. Same for the laundry room. In an exhaust only system, how are these rooms dealth with? Are they just not ventilated?


Balanced System
Description: Use an ERV or HRV, ducting as per install guide.

Pros (relative to exhaust only system)
- filtered fresh air to all living areas and bedrooms
- takes care of laundry room too
- energy efficient
- less risk of pulling warm humid air into the envelope (leaks) during AC season
- less risk of pulling air in from the attached garage 

Cons (relative to exhaust only system) 
- I don't know which ERV or HRV to select, and sees like local HVAC resources aren't going to be that helpful on this topic
- higher probability of not getting the design or equipment selection correct leading to noisy or inefficient operation, or discontinued use
- possibly noisy operation, as reported on some GBA blog posts (very undesirable for me!)
- somewhat more complex to get settings/operation correct
- higher initial cost, and maybe MUCH higher if I want to consider a very high quality unit for less noise
- higher future maintenance costs on the unit

BabyBldr-

My location is so different from yours, that my experience may not be directly applicable to your house. I am in a high mountain valley in Colorado, so dry, cool, heating-only climate here. I have a Venmar Eko 1.5 HRV, which uses the ECM motors. (I would recommend ECM motors for an exhaust-only fan or an ERV or HRV.) The unit is mounted in my conditioned crawl space, and is arranged such that it pulls stale air into the unit from the crawl space, so venting air from the living area into the crawl space. The fresh air is blown into the outlet side of the forced hot air, natural-gas fueled furance, so I already had duct work available.

There is no noticeable noise from the HRV fans in terms of vibration or hum. The unit is hung on springs in the crawl space. On low fan speed, I cannot hear the airflow, but I can hear it on high speed. It is not objectionable to me on high speed, but it is certainly audible, and if sitting near a floor vent, the draft can be objectionable on high speed. I leave it in part-time recirculate mode most of the time, where it pulls in fresh air 20, 30, or 40 minutes an hour, and recirculates the remainder of the time. In this mode, the fan or fans must run on high speed, as the sound is audible. (I need to hook up a Kill-a-Watt meter again to check to see if one fans runs on high when in recirculate mode, which would made some sense.)

However, my reason for using recirculate mode may not be applicable to your situation. The humidity is so low here that reducing the fresh air flow slighlty reduces the dryness in the house. Further, I have passive solar heating (what some would call solar tempering) in a portion of the house, and want to circulate that heat into the remainder of the house. When I add a humidifier, I may modify my strategy on the HRV. At this point, I most often use it on 20 min. of fresh air, 40 min. of recirculate.

I justified the installed cost of the HRV (just under $2000) based on running the HRV full time on the fresh air setting at low speed. Since I actually use it less than that, the payoff is worse than what I originally computed. But here is that original analysis comparing the use of an exhaust-only fan used to exhaust air from a sealed crawl space, and to suck in fresh air through leaks, with a HRV for my particular application:

The exhaust fan is rated at 80 CFM, while the HRV is currently operating at about 49 CFM, so not quite an apples-to-applies comparison. The exhaust fan was assumed to be a high efficiency ECM fan that is rated at 24 W. I measured the power on the HRV on low speed, and it uses 26 W.

Over a year that includes a typical heating season with 7317 heating degree days (deg-F*days), the exhaust-only fan uses 210 kWh ($21 at $0.10/kWh), but exhausts air that must be replaced by heating fresh air, and that requires 4450 kWh of heating energy, or about 152 therms of natural gas, or approximately 148 CCF at roughly $0.90/CCF, or $133. (Natural gas prices are variable in this area, but that is an estimated average.) Total yearly cost for the exhaust-only fan is $21 + $133 = $154 at today’s prices.

The HRV on "Min" setting uses 229 kWh ($23 at $0.10/kWh) over a year, exhausts air that has an energy content of 2726 kWh, but recovers 2262 kWh, leaving a net requirement of 463 kWh to heat fresh air, or about 16 therms of natural gas, or 15 CCF at $0.90/CCF, or $14. Total yearly cost is $37, but fresh air rate is 49 CFM versus 80 CFM for exhaust-only fan. HRV supplies "balanced" air pressures, while exhaust fan results in negative air pressure balance, with balanced considered preferable. (By using a different switch setting on the HRV, the fresh air rate could be increased.) So the 229 kWh to run the fans results in an energy savings of 2262 kWh in air heating requirements, but electrical power is high-grade energy worth about 3 times as much as low-grade heating energy.

Net saving with HRV is $96 per year, but initial cost (installed) was $1978.50, including the cost savings of not installing the exhaust-only fan. If energy prices increase at 7% per year, it would take 13 1/2 years to recover the initial investment, ignoring the investment potential of the initial investment. Since fan motors may not last 13 1/2 years, the HRV will likely never pay for itself.

I have the RenewAire EV200 in my home and also rental house in WI.  Both pull air from 2 bathrooms and the general kitchen area.  My rental has dedicated ductwork delivering fresh air to the MB, DR, 1st to 2nd floor stairwell and basement.  In my house, the fresh air dumps into the return of my forced air furnace. 

A percentage timer operates the single speed unit a portion of each hour based on the house volume and intended ventilation rate.  Mine runs between 20-60% run time and up to 100% when having guests.

A push button is located in each bath and kitchen area for 20-40-60 minutes on demand.  The unit is mounted directly to a wall using isolation parts included.  Mine is in the basement and rental in a second floor closet. The EV200 uses 157 watts when running and less than 1 watt standby power when cycled off. 

The ERV rejects some humidity from coming in during summer (as long as you have a dehumidifier or A/C operating, since it is only exchanging and not condensing moisture out of the air).  It doesn't deplete all of the humidity out of the house during winter as it recaptures some.  An HRV has only sensible (heat) transfer between air streams.  My units do not have drains and both are mounted upside down which made the installation of ductwork easier. 

The ERV can be the only bath exhaust as long as you plan sufficient airflow from each room and the vent is placed away from the door and high in the wall or ceiling, and the ERV sized for the total cfm needed.  It is a supplement to my exhausting range hood for lingering cooking odors and moisture.  My ERV pulls 75cfm from the kitchen, 47cfm from the first bath, and 55 from second bath.  The same total volume of fresh air comes back into the house when the central exhaust system is operating.

You could also pull air from a laundry or interior bathroom by placing ductwork in the walls or ceiling and connected back to the ERV.  Choose ductwork capable of your intended exhaust and balance with volume dampers or grilles.  Seal the ductwork and joints with foil (not duct) tape.  Check the Home Ventilating website (hvi.org) for independent results for efficiency and electrical use.

A room air purifier could be used as air filtration in a very tight home. You would want filtration on the HRV/ERV but I dont think it would need to be HEPA.

When you are talking about a tight house you will have a lot less dust etc from air leaks. In many cases a mini split will be used and there will be no ducts to provide filtration.

To me a tight house is the perfect place for an air purifier. You will get the benefit of HEPA filtration along with a charcoal filter for gases and odors. I have used Austin Air as they have large HEPA filters along with pounds of activated charcoal versus a few ounces with most others. They can be run continusly without then energy penalty of a blower.

I recommend staying away from any that produce ozone.

Posted By Roberth on 25 Oct 2011 12:41 AM
A room air purifier could be used as air filtration in a very tight home. You would want filtration on the HRV/ERV but I dont think it would need to be HEPA.

When you are talking about a tight house you will have a lot less dust etc from air leaks. In many cases a mini split will be used and there will be no ducts to provide filtration.

To me a tight house is the perfect place for an air purifier. You will get the benefit of HEPA filtration along with a charcoal filter for gases and odors. I have used Austin Air as they have large HEPA filters along with pounds of activated charcoal versus a few ounces with most others. They can be run continusly without then energy penalty of a blower.

I recommend staying away from any that produce ozone.

Most name-brand mini-splits have decent filters, but SFAIK none have full-on HEPA filters. Cleaning/replacing the filters periodically is important for maintaining the efficiency of a mini-split. Even an ECM drive variable speed blower uses a lot of power to push air through a year's worth of accumulated crud.

Ducts don't provide filtration, but they do accumulate junk and can become a breeding ground for mold under some conditions.  (Duct cleaning services are usually a waste of money though.)

I am quite aware ducts dont provide filtration. But air handlers connected to the ducts provide filtration. Some people like to run the blower 24/7 to circulate air and provide filtration too. If you are relying on a HVAC system to provide filtration what do you do on the days it may not run much or on days it doesnt run. The fujitsu has a washable filter and an "ION deodorizer". I have never been impressed with Ionic type filters. I would also question if the ION filter produces ozone. What is level of filtration for the washable filter.

Posted By Dana1 on 25 Oct 2011 02:09 PM

Ducts don't provide filtration, but they do accumulate junk and can become a breeding ground for mold under some conditions.  (Duct cleaning services are usually a waste of money though.)

Thanks Roberth and Dana1 for your input.  After I posted about the filters (above), I went off and did a bit of reading on HEPA and MERV filter ratings and learned a little. I realized I don't really need a HEPA filter. Sure I'm tyring to improve our indoor air qauality, but I'm not going for "clean room" standards. ;-) So, in the end, I settled on the Venmar EKO 1.5 HRV based on reading numerous threads here, and on its efficiency rating.

Dana1, I wonder if you could elaborate on your statement. I'm  just seeking more info since I'm in the planning/buying stages of the dedicated ductwork for our HRV. I'm especially wondering about the possibility of condensation inside the main 6" round ducts (in the summer, when wam humid air is being drawn in as the fresh air source; or in the winter when moist warm air is being exhausted from the system)... Like if the main ducts were "too long" - but from the documentation for the HRV, "too long" seems to be very subjective.

In an HRV system what condensation occurs usually happens in the HRV's heat exchanger, not the ducts, since that's where the temperature shift occurs. In places with high summertime dew points an ERV is a better solution, since it removes a good fraction of the incoming humidity, passing into the exiting airstream. HRV/ERV is also a 365 day/year situation and somewhat self-purging of contaminants, as distinct from heating system ducts in unconditioned basements that may stagnate for months on end, allow molds to get going in the accumulated debris. Flex duct is the worst from an accumulation point of view due to the uneven interior surface, but rigid ducts are not immune. The smoother the interior are and the better-relieved the bends are the less accumulation occurs.

I agree with Dana1's comments about the condensation mostly occurring in the heat exchanger located inside the HRV. Therefore, the HRV has drains that handle the water, and that water must be dealt with. In my case, the water is drained from the HRV located in the crawl space to a nearby pump, also in the crawl space, that handles condensation from the furnace. The pump sends the water to the sewer drain pipes (that are also located in the conditioned crawl space), a code requirement in this area.

The ducts for the fresh air into the HRV and the exhaust for the stale air from the HRV are insulated in my case that has the ducts located in a conditioned crawl space. The insulation serves a number of purposes, but it should help minimize condensation in the duct work. For example, on hot humid days, it minimizes condensation due to cooling in the fresh air duct. Another purpose is to keep the ducts from acting like heat exchangers with the air in the conditioned crawl space. For example, on cold days it reduces the amount of cooling by the fresh air duct and the exhaust duct on the crawl space, and the converse on hot days.