You don't trap in harmful air pollutants because you have an ERV or HRV. Of course they add some additional cost, but you still end up saving on heating and air conditioning.

ERVs and HRVs have speed controls, so you can control how many air exchanges you have per hour.

We have an ERV in our house....it's silent, we use it to vent the baths as is required by code anyway. It exhausts the air through the baths, but brings fresh air into the plenum so it is distributed throughout the house. Each bath has a button...press it and it runs for 15 min and shuts off. We also have other controls so we can turn it on and let it run, setting how often it automatically comes on every hour. If need be we can set it on full to exchange the entire air in the house in about 3 hrs. But we typically don't do that. The air can get stale in the winter when the house is shut up, but we like open windows and use natural ventilation most of the year.

Our place is now about as tight as you can make a structure 2/3rds of which was built in 1952. The ERV ducted into the HVAC system seems to work very well; odors do not linger, there is never any stuffiness. Our heating and cooling energy costs are about half what we spent on the similar, but conventionally sealed and insulated 14 year old house we moved out of.

Great question and replies so far. Congratulations and thanks for learning more about the key strategy for energy efficiency in homes.

Are we going to find problems with tight houses?

We already are and it depends, as always, on the details. So many variables and specific situations but the take away should be this: You will have more control over your conditioned air and Indoor Air Quality with a tight building envelope. Leaky, poorly insulated envelopes could be making the IAQ worse by introducing more soil gases like radon, CO from garages, or creating mold problems inside walls by sucking humid air past cold framing. With a tight building envelope, you can control where the air comes from, where it is going and how much fresh air is being introduced.

Will fresh air introduction increase energy costs?

Yes. But usually not more than having a lot of air infiltration and exfiltration and its usually a healthier result. ERVs and HRVs are not the only way to introduce fresh air to the house but they address this concern with air to air heat exchangers to help capture the energy spent to condition the indoor air. I think its important to choose a ventilation device that uses an ECM motor as they use a fraction of the energy of more typical fan motors. Currently, this means going with an HRV.

How do you know if HVAC contractor did the right calculations?

Generally, you should never rely on the HVAC contractor to do your load calculations. Hiring a third party energy rater or certifier is usually money very well spent. The minimum calculations should be a Manual J. I suggest getting Energy Star certified to alleviate much of the concern in this area.

People should be aware that blower door test proven, tight homes are required by international building codes. So is fresh air introduction namely through the ASHRAE 62.2 ventilation standard. Search; Understanding Ashrae 62.2, if youre not familiar with it. Local codes generally dont enforce these important details. I think people in the future will look back on Blower door tested airtightness as we look back on insulation requirements. "They used to require insulation without ACH50 numbers?.. Amazing!" The best thing about blower door testing is that the resulting numbers and measurements are so much more meaningful than R value, which is very tricky to accurately evaluate.

Blower door proven airtighness is fairly solid science at this point and will be enforced hopefully in the near future. Things will really change in the coming years regarding ASHRAE 62.2 and fresh air introduction. Health science is trickier to pin down but I feel the take away in this area is to build a balanced ventilation system that can be easily controlled (turned up or down). The bigger and less open the floorplan, the more important it becomes to keep fresh air ventilation ducts separate from heating and cooling ducts.

Thank you all for your replies. Looks like I have some homework to do! I am a bit put off by thinking about yet another mechanical system to budget for and maintain, but I do understand how critical it is to control moisture and air quality in a new home.

rwiegand, your comments about odors not lingering and the house not feeling stuffy are encouraging.

Brian, your explanation of having more control of the air is a good way to put it. I have read a bit about load calculations and decided that we should use an energy rater service. (Any recommendations for upstate SC, a bit south of Charlotte?)

AnnieD, is your system a continuous system? Or did you decide to use on-demand since you open windows much of the year?

I assume the local climate will have a bearing on the design of a ventilation system? Summer's humidity will be our challenge.

We turn ours on and off as desired, though we could set it for continuous.

We are in NC, so I understand what you mean about humid summers. Our ERV helps pull out the humidity during the summer. Unlike Annie, we have ours on continuously although we do change the speed sometimes. We don't turn it off when opening windows because it would be too easy to forget to turn it back on when the windows were closed and the house it so tight it needs the air exchanges.

Annie - the button in your bathrooms turns the ERV on? I thought those buttons just boosted the speed for the 15 minutes.

Yes, in our house, it turns it on. We normally keep it off, but it runs for 15 min when we press the button.

I'm not sure what it does when the unit is on all the time. I suspect it turns the fan on for 15 min. What I mean is that, for example, when we turn the thing on to run continuously, we have it set to run for 15 min out of every hour. So I suspect hitting the button will turn it on for 15 min if the unit is in the "45 min off" part of the cycle.

My folks built a tight house back in the 80's and experienced nothing but problems since. Largely due to the high humidity levels due to limited air exchange. In the summer when humidity outside is high, they relied on 24-7 use of their air conditioner, solely to dry out the incoming air, plus often a dehumidifier. Unfortunately, the house often still felt "stale". In the wintertime, despite exterior humidity plummeting, they still experienced 60% inside the house (summertime was upwards of 70%).

Thanks to the recent introduction (and improvements to) HRV systems, my parents installed one this year. It ran continuously for 3 months (January - March) and cost them about $300 to run during that time. Now, keep in mind that there was 30 years of moisture in that house...

Their house now sits below 40% humidity (they don't like it below 30 for their comfort), has regular fresh airflow and they expect their heating costs to be LESS next winter since the removal of the dampness in the air actually makes a cooler room feel warmer.

I also installed an HRV, and it's wonderful. In my brand new construction, 1 month of continuous running brought my humidity under 40% and provides plenty of fresh air intake. I didn't see nearly the increase in costs. My place always feels fresh.

The cost of the unit was around $1000, and it has a programmable "thermostat" that can be set to a variable or continuous operation. The actual install we did ourselves, which was surprisingly easy. Not even 4 hours start to finish, with just one hole cut in the rim joists.

After seeing what my parents experienced for the last 30, $1000 and 4 hours seems like a pretty easy way to ensure future home comfort.

--Are we going to find out in a few years that our very tight houses are trapping harmful air pollutants inside?

we have already, homes that were sealed & no provision for make up air installed. build tight and ventilate right. lots of ways to do this...
--If you have to install a system to bring fresh air inside, doesn't that additional cost offset some of the savings of insulation?
here in hot humid La. we take our required measured fresh air and duct it to return air. dehumidified & cooled before entering living space.you control where it enters, how much enters..its all about measured controlled fresh air.
here it is erv, or my favorite...ventilated whole house dehumidifier.
--How do you know if your HVAC contractor has adequately calculated replacement air needs for a really tight house? Is it one of those things that a few years down the road we find out that another variable needed to be in the equation? (This point really weighs on my mind.)
don't rely on hvac company. have independent load calc...duct sizing & duct design. then bid these unbiased calcs to hvac companies. inputs control sizing...if they are inaccurate...the sizing of the system...duct design & sizing will all be off. you have to provide details...types of insulation & projected air tightness of house. then have air tightness of house & ducts tested at proper stage.

best of luck

"Ventilated whole house dehumidifier" - How are these different from central a/c system? I was reading various articles on Ultra-Aire's website and see that these units supplement an a/c system. Do they run all year? It seems like they are mini-a/c units that dehumidify but not to the point to make the air as cool as an a/c?

Interesting...our house is pretty tight and we had to add a humidifier as it gets too dry in the winter...of course we use our woodstove daily which is really dry heat...

How do we find an independent people to do load calculations? What are they called?

--Are we going to find out in a few years that our very tight houses are trapping harmful air pollutants inside? That discovery has already been made, and the corrections made to building codes and recommendations.

--If you have to install a system to bring fresh air inside, doesn't that additional cost offset some of the savings of insulation? Yes, but only "some"

--How do you know if your HVAC contractor has adequately calculated replacement air needs for a really tight house?
They have software to calculate this, based on engineering calculations and house size and climate.

IowaCommute, I imagine an energy rater contractor could help you find someone who does HVAC calculations. I think Resnet is the trade association of contractors who do energy audits and ratings. (Link provided.)

I've also found Energy Vanguard.com who does HVAC calculations but have not contacted him. He has a lot of very helpful information on his website and blog.

Here is a link that might be useful: Resnet, Residential Energy Services Network

Thank you Nanj. You asked some of the questions I have wondered about so I have bookmarked this thread. Good luck on your home.

nanj's info is correct.
sorry to have not replied...but internet
has been out.

over at hvac-talk.com there is a link to a load
calc program for homeowner to do..for a small
fee for 30 days. $50 I think.
the pros there could also give you good input.

best of luck

best of luck.