Posted By FBBP on 18 Mar 2013 01:16 PM
lbear - where do you get 61º supply air temp from?? If the exchanger core was working at 100% efficiency it could only raise the incoming air one degree for every degree it pulled out of the exhaust air so at BEST it would split the difference. So with 72ºf air going out and -30ºf (Joel indicates he is in western Mn, with out know the exact location, this is probably close to design temp.) air coming in the result would be closer to 21ºf. Certainly not something you would want dumping into living space.
The resistance heater that some HRV employ are usually defrost mechanisms and do not heat the incoming air. The unit you referenced appears to use indoor air for defrost. If there is a resistance heating module in any unit, it would require an breaker of upwards of 30 amps.

There is absolutely no reason a well designed HVAC unit would create any type of imbalance. If it is just heating the air in the house it will not effect the inside outside pressure at all unless it is still an open combustion unit. In that case the installer would need to bring in combustion air so it still would balance. If the fresh air side of the HRV was dumped into the return side of the f.a. furnace, it would still balance through out the house and would heat the incoming air as it passes over the furnace heat exchanger.

I had an industry expert tell my WHY some HRV/ERV manufacturers are "OK" with using a non-dedicated HRV/ERV duct system. He said flat out, it's all about the money. He said that they do not want to lose out on a huge market segment, the retrofit people. If they only promoted HRV systems with dedicated ducts, that would leave out the countless amounts of customers who want to retrofit their current home with an HRV/ERV. Therefore he said that even in their install manuals, it will clearly state that a dedicated system works best for a HRV/ERV and that is how the engineers designed the systems and cfm airflow ratings. When it is retrofitted into an existing HVAC setup, there are too many variables that the HRV manufacturer can't control or know about.

The HRV/ERV industry does not want to lose millions of dollars to the retrofit customers, so they will allow a non-dedicated duct system, but to cover themselves they will disclaim that the system was not engineered/designed to work properly and efficiently in a non-dedicated system.


According to building science experts at GBA:

"The best ventilation performance and lowest operating cost comes from an HRV or ERV with dedicated ventilation ductwork. Such a “gold standard” system should be designed to pull stale air from bathrooms and laundry rooms, while introducing fresh air to the living room and bedrooms.... The worst systems I've seen are ERVs or HRVs hooked up to space-heating ductwork."


Running the HRV through the furnace fan will cost you big time. Furnace fans are notorious for high energy use. Depending on the furnace fan size they typically pull 250watts - 850watts of power. HRVs pull around 85 watts (2,500sqft home - 140cfm)

So yes, an HRV can be retrofitted into an existing HVAC system. Although it will not be the most efficient design and it will use more energy than a dedicated HRV duct system. It is also a known fact that central air systems are highly inefficient when compared to ductless mini-splits, the main reason being is the duct work.


As far as efficiency goes, my guesstimate was wrong. It showed the Winter Design Dry Bulb Temperature of Minnesota as -25F and the Summer DDBT of 93F. It has both extremes, too cold in the winter, too hot in the summer, but that is the norm for a northern interior state like that. Again, why do people live in Minnesota?

Venting a home is a necessary evil. It must be done for occupant safety and health but it's the way it's done that can cost you greater energy loss. One can build a leaky home (not wise) or one can just punch a 6" hole in their wall (not wise either). The HRV/ERV meets the venting needs and does so efficiently. You can kill numerous birds with one stone by tying in all the bathroom vents into the HRV. So you get bathroom venting and home venting in a controlled unit with only 2 holes in the side of your home vs. 4 roof penetrations. A wall vent is easier to seal properly than a roof vent.

Lbear - I can see how retrofitting an HRV into existing ductwork could be very inefficient (especially if attention wasn't paid to sealing the ductwork ). That said, in MN I think the extreme outdoor temp swings make it hard to install a fully ducted HRV system. I'm glad I came across this forum to bounce ideas off of people that know what they're talking about. I've talked with some local HVAC people who don't seem to understand building a HRVs and building a house with a tight envelope. I'm currently renting a stick frame house (not a very tight envelope at all) built in ~2002. It has forced air HVAC with a gas furnace. The original builder installed an HRV and fully integrated it with the HRV (No exhaust ducts in the bathrooms). When I moved in, the HRV unit was unplugged. The owner said it had never been used in the 10 years since the house had been built!!! When I asked a local HVAC guy what to do with it, I was told to put it on a timer & have it run 2 hours on/1 hour off all year round. By the way, we live in MN for the good looking women :-)

FBBP - I'm 1/2 way between the Twin Cities & Fargo. Natural gas is available. I want to go geothermal for 2 reasons: lower operating costs over the long run & the 30% tax credit that makes installing geothermal much more cost competitive to install. We have cheaper electric costs. Also without a combustion furnace, I have one less thing to worry about backdrafting. We are planning to have a gas fireplace, but that will have it's own dedicated air combustion source.

There actually are options other than venting. There are indoor plants that can provide even better air quality: http://www.wolvertonenvironmental.com/air.htm

Posted By joeldunn21 on 18 Mar 2013 11:56 PM
Lbear - I can see how retrofitting an HRV into existing ductwork could be very inefficient (especially if attention wasn't paid to sealing the ductwork ). That said, in MN I think the extreme outdoor temp swings make it hard to install a fully ducted HRV system. I'm glad I came across this forum to bounce ideas off of people that know what they're talking about. I've talked with some local HVAC people who don't seem to understand building a HRVs and building a house with a tight envelope.

That's typical for HVAC and contractors. When I hear them say, "houses have to breathe, so we build them leaky", I cringe. When a house leaks air from the walls, windows and ceiling, one cannot control the amount of leakage and it also presents other problems like water & bug intrusion. Too many contractors are stuck in the 1900s when it comes to building. Most HVAC people are clueless. They despise ductless mini-splits or have no clue on what they even are. A lot less expensive installing a ductless mini-split vs. a complete central air system with duct work running throughout the home.

Posted By Torben on 19 Mar 2013 12:25 AM
There actually are options other than venting. There are indoor plants that can provide even better air quality: http://www.wolvertonenvironmental.com/air.htm

The biggest problem is that 2012 IBC requires mechanical ventilation on tight homes. No way code will allow a tight home with no mechanical venting and just a bunch of indoor plants.

Sure one can install a HRV and just turn it off and rely on plants but I would have a CO2 detector and humidity levels must be observed, as plants add moisture to the air.

Didn't they try the sealed BioSphere and it turned into a huge disaster? I mean in real life not the Pauly Shore movie, which was also a huge disaster but a movie disaster.

This thread has me kind of confused, at first it seemed pretty straight forward, you want to have an HRV (or some kind of air exchange) with a SIPs (or tightly built) house.

It also seemed to make perfect sense (I think it still does) to pull the "dirty" air from the areas you would typically vent from. (Bathrooms and Kitchens)

Then it got muddy for me, It was stated that in the northern climates (colder) your going to be putting some very cold air back into your central living spaces if you use a seperately ducted system. (Though I still don't fully understand how the amount the system can heat up the incoming air by recovering some of the heat from the air being vented out is calculated)

It was also stated that because of this in northern or colder climates you would want to run the air through your furnace system/ducting to further heat it. This was then disputed and it was said there are other ways to heat the air up but some said that's not really effective/efficient....

To me there is no question that you need ventilation, what's confusing to me is how is there not an established effective recommended way to do this? We have a large portion of the US and all of Canada building homes in the afformentioned climates I would think there would be some good products and practices for it that don't dump near freezing air back into the home living spaces.

Am I missing something? I am quite interested in the answer as I live in central WI and I am planning to build a SIPs home.

HRV / ERV s exchange air thru a core similar to a radiator,....... but instead of air to water temperature transfer....... it is air to air temerature transfer, ....the incoming air is tempered by the out going exhausted conditioned air, heated in winter or air conditioned in summer ....... "Energystar is also requiring make up air, but in my opinion it should not be mandated or code required. ...There is still air leakage around doors and windows, you stil open a door to get in and out of the home ( guess what comes in with you)......... ERV's - my opinion -waste of money in southern climates,

some interesting reading from Martin. While I don't agree with all he has to say, Martin surely has the background to say it.
http://www.greenbuildingadvisor.com/blogs/dept/musings/are-hrvs-cost-effective

Ventilation requirements for cold climates
1) need to bring in fresh air to all rooms up to ashrae standards (either occupant load or room/size)
2) this air must be mechanically induced (not through windows or leaks) and must be tempered to 55ºf
3) must not create pressure imbalances.

How you met these requirements can vary greatly.
Remember also that in the western cold climate, high humidity is almost never an issue. Bathroom fans are not run in the winter to remove humidity, strictly fart fans.
While summers can have a few warm days, they are almost never warm humid days so 90 to 100ºf temps are not as big a deal as they would be with 98% r.h. Summer nights also tend to be cool.
Pick your heating system than your ventilation system. With strictly floor heat you need to put in some sort of duct work. If you deem it necessary to have AC you would take that into consideration.

Most areas that have natural gas are not effective areas to use geo. Unless you need AC.

The more money you put into the envelope, the less money it makes sense to put into the heating system. If your house only requires minimal heat, the pay back of a geo system might not happen.

One thing I have not hear discuss much is using mini splits for cooling and shoulder season heating and some other type when you really need heat. I guess it would depend on your cost of power.

When installing bathroom/kitchen fans, if your building allows, don't put them in the ceiling. Put them high on the interior wall and wall stack them down to the next floor lower prior to venting to the outside. This gets rid of the thermal stack effect.

Earth Tubes are another option for tempering cold incoming air with very little energy cost.

Posted By pcastleberg on 19 Mar 2013 09:13 AM
This thread has me kind of confused, at first it seemed pretty straight forward, you want to have an HRV (or some kind of air exchange) with a SIPs (or tightly built) house.

To me there is no question that you need ventilation, what's confusing to me is how is there not an established effective recommended way to do this? We have a large portion of the US and all of Canada building homes in the afformentioned climates I would think there would be some good products and practices for it that don't dump near freezing air back into the home living spaces.

Am I missing something? I am quite interested in the answer as I live in central WI and I am planning to build a SIPs home.

Home venting is actually a new phenomena to the residential building industry. In commercial buildings it has been around a long time but residential is a new animal.

Typically, residential homes had no mechanical ventilation because homes were built leaky and air intrusion came in through walls, windows, doors, ceiling, etc. The 2012 IRC is the first time they are addressing it properly in residential homes.

There are many ways to skin this cat but the most energy efficient way is mechanical HRV/ERV ventilation with a dedicated duct system. In extremely cold climates they offer a heating resistance element strip within the return duct to help preheat the air so it's not throwing freezing air back into the home. So in a -25F day, the HRV would temper the air and the heating element would heat the air to higher levels.

Home venting is actually a new phenomena to the residential building industry. In commercial buildings it has been around a long time but residential is a new animal.

Typically, residential homes had no mechanical ventilation because homes were built leaky and air intrusion came in through walls, windows, doors, ceiling, etc. The 2012 IRC is the first time they are addressing it properly in residential homes.

There are many ways to skin this cat but the most energy efficient way is mechanical HRV/ERV ventilation with a dedicated duct system. In extremely cold climates they offer a heating resistance element strip within the return duct to help preheat the air so it's not throwing freezing air back into the home. So in a -25F day, the HRV would temper the air and the heating element would heat the air to higher levels.

Lbear - I put in my first hrv back '83 and we have been using make up air and combustion air since the late 60. There is nothing new about venting residential homes in cold country. It just becomes more important to do it right as the homes get tighter.

Read Joe at http://www.buildingscience.com/documents/insights/bsi-053-just-right-and-airtight. My first hrv was a result of this program (Canada's R2000) I'll let Joe describe the shortcoming os his program.

Lbear please reread http://www.buildingscience.com/documents/insights/bsi-022-the-perfect-hvac

"To provide ventilation, a perfect system would provide separate ducted supply and return air systems. To reduce the energy used to heat or cool this ventilation air, a Heat Recovery Ventilator (HRV) can be used to transfer heat between the supply and exhaust streams as well as to provide the fans needed to move the air."
The separate duct systems ARE the supply and return systems of a standard forced air system. You then put the hru between the two. In cold climate the heating unit is running anyway so mixing the air requires no additional running of the furnace fan. (if the system is not over designed it will come on between every ten minute to once an hour which will provide for enough mua. If you need more at the shoulder seasons the units can be reverse interlocked to let the hrv drive the furnace motor.) Sure if you want to spend the money on a more efficient motor be my guest.

The cost of running the motor on a gas fire f.a. furnace will be considerably less then running a resistance heater to temper air for a stand alone hru system. Read Martin at http://www.greenbuildingadvisor.com/blogs/dept/musings/designing-good-ventilation-system and I think you would have to agree the the experts are far from united on an approach. They seldom completely agree with each other all the time and at time don't even agree with themselves. Read Riversongs latest musings and he has done what would appear to be a 180.

You are in an ideal climate to consider using earth tubes for your ventilation source. (Essentially your intake air comes in through a buried pipe to take advantage of the earth temperature to warm up the incoming air.) Instead of having to warm up -25 degree outside air you only have to warm up ~40 degree air. This incoming air can be routed through an ERV/HRV and the outgoing air exhausted directly. I've included a link to a zero energy home that used this. http://www.homepower.com/articles/net-zero-performance?v=print

Posted By Torben on 20 Mar 2013 11:54 AM
You are in an ideal climate to consider using earth tubes for your ventilation source. (Essentially your intake air comes in through a buried pipe to take advantage of the earth temperature to warm up the incoming air.) Instead of having to warm up -25 degree outside air you only have to warm up ~40 degree air. This incoming air can be routed through an ERV/HRV and the outgoing air exhausted directly. I've included a link to a zero energy home that used this. http://www.homepower.com/articles/net-zero-performance?v=print

Is that code approved?

What about radon infiltration?

The code is going to be silent on something as unusual as earth tubes. It would need to be an engineered system (similar to most SIP structures). High radon areas and tight homes are a bad combination irregardless. The earth tube at least have air circulation from above ground. Radon requires specially detailed active foundation ventilation that bypasses the living space. That not a situation in which I would care to live.

Lbear - I spoke with one of my local HVAC contractors. He agrees with you about having dedicated HRV ducting. When I asked him about my concerns over cooler air venting in to the living spaces during the winter, I was surprised by his answer. Instead of venting the fresh air return directly into living spaces or patching it into the HVAC, he simply lets the fresh air vent directly into the mechanical room where the HRV unit is! While that would keep pressure in the house equal & still exhaust stale air, it doesn't make much sense to have your "fresh air" pumped into the only room in the house you never live in!

What are your thoughts on this approach? (I definitely wouldn't have to worry about cold drafts during the winter!)

Speaking of HRV's, is there much of a difference between various brands?  My HVAC constractors in this area are using Carrier or Trane.  I can't find any good specs/review/data on them.  The Aldes systems referenced earlier in this thread seems a bit more credible simply because they post technical specs for their products online.  Their ZRT terminals make a lot of sense with their motorized dampers.  I can't find any useful into on the terminals my local HVAC guys use.

Posted By joeldunn21 on 24 Mar 2013 11:04 PM
Lbear - I spoke with one of my local HVAC contractors. He agrees with you about having dedicated HRV ducting. When I asked him about my concerns over cooler air venting in to the living spaces during the winter, I was surprised by his answer. Instead of venting the fresh air return directly into living spaces or patching it into the HVAC, he simply lets the fresh air vent directly into the mechanical room where the HRV unit is! While that would keep pressure in the house equal & still exhaust stale air, it doesn't make much sense to have your "fresh air" pumped into the only room in the house you never live in!

What are your thoughts on this approach? (I definitely wouldn't have to worry about cold drafts during the winter!)

Speaking of HRV's, is there much of a difference between various brands?  My HVAC constractors in this area are using Carrier or Trane.  I can't find any good specs/review/data on them.  The Aldes systems referenced earlier in this thread seems a bit more credible simply because they post technical specs for their products online.  Their ZRT terminals make a lot of sense with their motorized dampers.  I can't find any useful into on the terminals my local HVAC guys use.

If the HRV is drawing exhaust air from the mechanical room then it would be a BAD IDEA to have the fresh air return to be in that same room. If that's not the case, I don't see a problem with having the fresh air return being in the mechanical room. As long as the mechanical room door is left open so that the air can mix with the rest of the home.

I would lean towards putting the fresh air return in a place that it can be evenly distributed in the home where it will be conditioned/mixed so as to not cause any cold air pockets. Up high in a living room would be a good spot or at the end of a hallway.

I would stay away from Carrier or Trane HRV's. Haven't heard much good about them. Stick with the brands that manufacturers have published results and who have perfected HRV's. Companies like Trane or Carrier are just jumping onto the HRV/ERV bandwagon.

Posted By joeldunn21 on 24 Mar 2013 11:04 PM
Lbear - I spoke with one of my local HVAC contractors. He agrees with you about having dedicated HRV ducting. When I asked him about my concerns over cooler air venting in to the living spaces during the winter, I was surprised by his answer. Instead of venting the fresh air return directly into living spaces or patching it into the HVAC, he simply lets the fresh air vent directly into the mechanical room where the HRV unit is! While that would keep pressure in the house equal & still exhaust stale air, it doesn't make much sense to have your "fresh air" pumped into the only room in the house you never live in!

What are your thoughts on this approach? (I definitely wouldn't have to worry about cold drafts during the winter!)

Speaking of HRV's, is there much of a difference between various brands?  My HVAC constractors in this area are using Carrier or Trane.  I can't find any good specs/review/data on them.  The Aldes systems referenced earlier in this thread seems a bit more credible simply because they post technical specs for their products online.  Their ZRT terminals make a lot of sense with their motorized dampers.  I can't find any useful into on the terminals my local HVAC guys use.

joeldunn21,
your HVAC contractors are selling Trane and carrier, because that what they are dealers for, it has nothing to do with permormance,
If you talk to a Lennox dealer, they will be selling Lennox HRV's
you will pay them a premium, but you may noy have a choice, a lot of HVAC contractors will not stray from their "brands" and refuse to install an owner supplied HRVs

Posted By joeldunn21 on 24 Mar 2013 11:04 PM
Instead of venting the fresh air return directly into living spaces or patching it into the HVAC, he simply lets the fresh air vent directly into the mechanical room where the HRV unit is! While that would keep pressure in the house equal & still exhaust stale air, it doesn't make much sense to have your "fresh air" pumped into the only room in the house you never live in!

What are your thoughts on this approach? (I definitely wouldn't have to worry about cold drafts during the winter!)

Speaking of HRV's, is there much of a difference between various brands?  My HVAC constractors in this area are using Carrier or Trane.  I can't find any good specs/review/data on them.  The Aldes systems referenced earlier in this thread seems a bit more credible simply because they post technical specs for their products online.  Their ZRT terminals make a lot of sense with their motorized dampers.  I can't find any useful into on the terminals my local HVAC guys use.

Mechanical rooms tend to have water lines in them. Water lines tend to freezes when freezing air is dropped on then.

Mechanical rooms are designed to be kept closed for a variety of reasons. Cutting down noise and cutting down combustion byproducts from entering the sleeping areas are some of them. Many Codes require a closed door on the mechanical room. Might not be a concern if you are going geo (no combustion) but compressors do tend to make some noise.

Some cold climate codes also require that the fresh air is distributed to all living and sleep areas of the house. The only reason for not ducting and tempering is to save money.

Has anyone seen small-bore HRV ducting run concentrically (ie, embedded) inside of large-bore conditioned air supply ducts?

It seems like this would allow the low power continuous HRV fans to see the load they want (without having to push excessive ventilation air down the conditioned air ducting) while making double-duty use of the mechanical chases and supply and return registers that are already installed for the conditioned forced-air system. Of course, not each conditioned-air supply and return leg would need to be doubled-up this way if not required for the # of air changes spec'd for the HRV.

The cross-sectional area consumed by the HRV ducting could be made up by slightly larger-dimensioned conditioned-air ducting - or the system designer could get really clever and use flappers to push conditioned air down the HRV duct as well during the HVAC system's heating/cooling duty cycle.