I am building a 4500 ' house with a HVR also. My unit will have a fresh air pelum that will allow conditioned air to enter as you create a neg. pressure. Remember one of your ducts to the HRV should be coming from the bath. Who says you have to run a bath vent for 20 mins? With a house that tight the unit may run several hours a day but what you spend in electric will make up for heat gain.The spray foam is a good idea but I am also putting 1" iso board on the exterior sheathing so less heat will telegraph thru the studs

Re: bwood74

I think there is some truth to your point of view. That essentially correcting one set of problems creates a whole new set to deal with. You may want to consider a humidistat or timer for your bathroom fans.

The issue has been settled by experts with the general idea being seal it tight and ventilate right.

Fans use orders of magnitude less energy than heating or cooling.

Foaming an entire house in central Va is probably overkill. You might look at what that is costing you vs sealing in other ways. 1 in rigid board foam over the envelope will cost less and do more by stopping the thermal break of the studs as has been mentioned.

Building an efficient house the smartest way is not always straightforward. In my neck of the woods (NC), foam was about $18k vs conventional of $4k. That difference would pay my entire HVAC costs for 10 years. And as it stands, my greatest loss is windows which foam obviously wouldn't touch. The windows are foamed around.

bx

I recently went through a new build and live in No. Va. I put an ERV in myself after the house was completed. here are some things I learned:

- as david mentioned, foam cost is a lot higher than other good alternatives. I chose blown cellulose which works great with 2x6 framing. We used spray foam in joist cavities around perimeter and in crannies where cellulose wouldn't work. We then had the interior of the house caulked. This package was a bit more than the pink stuff but a lot less than foam and works great.

- put extra insulation in the attic. Code in my area is R30, I went with R40 blown cellulose. Small delta cost but this is where you will lose a lot of heat.

- be careful when using foam around window & door frames. You want the foam in there but if they use a product that expands too much it can warp the frames.

- inspect the house yourself after the insulation is done. I could not believe how many crannies were missed and areas where the insulation wasn't done right. Biggest issue was around fireplace inserts.

- If you use blown cellulose, make sure they come back a few days after the initial application to fill in the tops of the stud cavities whwhere you can get "smiles" when the cellulose sags a bit as it compresses. This was part of the insulation package cost.

- Use high quality fans in the bathrooms. I always hated the noisy fans in my other houses and was pleased to find out that for just a little more money I could get high quality quiet fans (see Broan and Nutone). Make sure that they put bird/rodent screens on the outside vent penetrations. I would also add some additional tight mesh screening on those vent caps to block stink bugs which can get past the rodent screens and into the house through these vents. I later added timers on all my fans so that I could push a button and the fan would turn off after a set period of time. See www.smarthome.com and do a sreach on the Insteon fan switch.

- The ERV is an important device, espcecially during the outgassing period when your house is done. All the glues and paints will continue to outgass for quite some time and the smell can be overwhelming. If you plan to move in during the winter like I did, you will want a way to get fresh air into the house. I wish I had added the ERV right from the begining. Bathroom fans aren't going to give you the fresh air replenishment that you will need.

- To make the ERV work with with the HVAC system, you will need tstats that have IAQ functions (Indoor Air Quality). I wound up replacing the original tstats with Honeywell Vision Pro IAQ tstats and programmed them myself. Connecting the ERV to the HVAC control is not as easy as it should be and can vary greatly depending on what model you pick and the funtionality you want. I discuss my challenge with the Broan unit I selected in the link below.

- I would look at a basement ERV install in a standalone configuration. If you download the Broan instllation manual, they provide some very nice pictures of the different methods for hooking an ERV up. I selected the standlone method and it works great.

- If you plan to add the ERV after the house is done, at least have the builder precut the penetration(s) for the ERV vents. For the Broan you will need one 6 inch penetration, most other units require two 6 inch penetrations. I had to cut my hole after the fact - through the stone veneer exterior - and it wasn't fun.

- I found that the tight house added one last complication and that was moisture build up in the basement. Our first summer in the house I noticed moisture spots on the concrete floor which i thought was mold. This issue was occuring on days where the temperatures are not too hot (so AC wasn't running) but outside humidity is very high - and these types of days are common in VA. I initially added a whole house dehumidifier to deal with that issue and it worked great. However after I added the Vision Pro stats (which have a built in humidistat) with the ERV, I found that you can program the vision pro to run the AC up to 3 degrees below the nominal AC set temp if the humidity is too high, esentially providing a dehumidifier funtion. I probably could have avoided putting in the whole house unit had I known about that feature before hand.

So the good news with my tight house is that energy bills are very low. Bad news is that I had to spend extra money after the house was done to deal with basement moisture and ventilation.

Good luck with the build

Here is a link that might be useful: Previous Post

The additional cost for 1/2" foam on 2500sqft is $3,300. Now this is mostly just to seal things up, then R19 is going over that.

That is a lot different than $18k.

Would it be feasible to run a bead of caulk up and down every stud against the osb or is that stupid.

I'm willing to do some things myself during construction to help seal things up, but really dont know what to do.

Is there a good place to research the ERV, HRV, humidity stuff? Like someone with actual data or research?

$3,300 is definitely better than $18k. $18k was for foam filing cavities and attic rafters. I still wouldn't do it but I think it is more reasonable. I had a $500 option for caulking and my builder talked me out of it. The fact is that not a lot of air moves across walls. I just sealed penetrations myself - particularly on the ceiling.

If you think about it - crown molding and the caulk against a wall is really tight. Ditto with the baseboard. I do think in a ceiling, there are tons of potential leaks. Around windows,doors - definitely a possibility.

I hate to talk people out of insulation and it definitely isn't my way of doing things. But you have to look at cost obviously. You might do a lot better using that $3k to pay for solar hot water or geothermal. Scratch that, you would do better to spend that money on geo or solar hot water.

Now if you are already doing geo, then obviously the payback is even worse but at least you are doing things in the right "order". Which is of course things that pay off financially first and then being efficient just to be efficient and environmentally responsible.

Spending the money on a solar hot water heater or geo prob would make more sense. I'd really like a solar hot water heater, but my house is going to be surrounded by woods, and the way my house sits its gonna be facing south and I don't want the grid on the front of the house. I've been told that geo isn't a big of a savings here in central Va as it would be farther up north.

I most likely will put R50 or 60 in the ceiling as the price difference isnt as great and thats where it makes the biggest difference. I may still drop the extra on the spray in for the peace of mind 40 years from now that I did all I could to insulate the best I could with the technology that was available.

Now if I don't opt for the spray in or try to do a lot of caulking, at what point do I know I can get away without the ERV? I guess the only real way to know is with a pressure test?

bwood - you aren't getting a leak test?

Obviously you probably won't get this but at least look into it.

In my locale, an energy star certification costs about $800 for your size house. It is like $550 plus $.10 a sq ft. That gives you an energy audit based on house plans, multiple inspections (primarily insulation and so called blocking), and a duct leak and and house leak test (blower door). That you can get but around here that gives you 5% off electric and NG for life. Pays for the certification eventually and you have the certification for resale (doesn't sound like that is an issue but you never know).

What you get is an estimated energy cost/use. And then changes to make and what their estimated effect.

To give an example - my conventional R13 walls cost about $200 a year in energy. So going R19 would save about $70 a year (very roughly). Going from R30 (code) to R40 in the attic saved about $50 a year. It cost about $200 so very worth it.

My energy costs wound up being a lot less than estimated despite the first (and only full year) being full of extreme temps - like last winter's cold. That just means that my walls actually lost considerably less than $200 a year.

My biggest regret is not doing something more on the walls only because you can't do anything more later. So doing either 2x6 or rigid foam on the outside would have been worth it just for my own piece of mind.

"Now as good as an ERV must be, it must really put a damper on the effeciency of all the sealing and high R values."

Having exterior air come in for better air quality is never without costs (either heating or cooling).

An ERV can recover some of the losses, making it markedly better than just opening a window.

bx

caulking between double studs and at the floor along top and bottom plates is exactly what you want to do. We paid for two guys to go around the house and caulk every nook and cranny that can't be filled with insulation. The goal is to cut air infiltration. To me it would make no sense to spend the money on a good insulation package and then not plug up these crevices. This is definately something a DIYer can do. Use a high quality caulk.

The goal is to cut the air infiltration down as much as possible to lower your energy costs, and that is what the foam and caulking do. But when you cut air infiltration down, you also cut down the fresh air supply to recoup what the freash air that you and your family use up and that is where the ERV comes in. It sounds like you want to do one without the other but you really need to do both.

The ERV is really a simple device. It sucks stale air out of the house while bringing an equivalent amount of fresh air into the house. The beauty of the device is that the heated (or cooled) stale air passes through a chamber that exchanges heat (or cool) with the fresh air coming in to minimze energy loss. So there is a cost for that freash air but what would you rather have: a really efficient house that has poor air quality or one that 85% as efficient energy wise but with excellent air quality?

If you are on the fence about the ERV, just put in the penetrations to accomodate one in the future. Live in the house and see how it feels - especially during the winter when you have the windows shut most of the time. If you decide you want the ERV, you can easily add it in yourself.

How is piping in fresh air before it is conditioned by the heat exchanger do? Is this some kind of option?

A fresh air intake is a lot cheaper than a ERV but is the equivalent of opening a window as far as energy use.

Build it tight, check the leakage, set up for a ERV in case you feel like you need it.

I have a pretty tight house (50% below ES standard before I fixed some things like a single door cat door without caulk). I don't have any fresh air intake or ERV and I don't notice anything. We used a lot of water based products and no-VOC paint etc. I have never noticed off gasing smells except from cabinets in a back office that were a different brand than the rest of the house. We vented that room a lot in the first year.

I may add a fresh air intake for mild outdoor temps. We have a large house to occupant ratio. My father had suggested cracking a window if we have a lot of guests.

bx

you can get either a passively controlled fresh air vent which works on pressure or an actively contolled vent that is tied into your HVAC tstat to bring fresh unconditioned air into the house. See link below.

I thought about using this type of vent but then decided that the ERV made more sense over the long run. Don't forget the mesh screening on the outside of the vent to kepp the stink bugs out of your HVAC system.

Here is a link that might be useful: Fresh Air Vent

thanks for the honeywell link sniffdog

I'm kinda late for the discusstion, but
wanted to contribute.
I'm all about the build tight ventilate right.
But..unless you actually test for tightness of building
envelope the question is if you will need fresh air or not.
Lots of homes are not tight enough to require fresh air.
And contrary to the install on the link provided by
sniffdog..I wouldn't run my fresh air supply along the roof line. Too hot in my climate. The temp of the air in august
would be too high for most central systems to dehumidify and
cool.

For the program I work with any home with less than .35
air changes per hour requires mechanical ventilation.
There is even a ventilation standard..ASHRAE 62.2
to determine how much (how many CFM cubic feet per minute) of air is to be added to the home.
But first you have to test the house with a blower door to
determine if the .35 ach has been met.

If in fact the house is tight enough to require fresh air.
then you want to carefully choose your location that the fresh air will be drawn from. clean it..measure it and condition it before it enters the living space of the home.

I usually install a 12x12" filter back grill under a porch
this allows you to filter the air, and the location is where air is cooler, as opposed to attic. an insulated sealed duct to the return side of the central system is added, this runs along the floor of the attic. At the return air plenum a barometric damper is installed, set to cfm as determined by number of occupants and ashrae 62.2
the damper opens for instance when stove vent is in use
and both bath fans are in use. as the fans turn off..the damper closes.
These fans are to vent the humidity out of the living space.
less humidity allows for RH levels to even out for better iaq and a healthy house.
When the house is not calling for air ( fresh air required to keep house from going into a negative pressure) the damper remains closed.

by putting the fresh air to the return side of the system,
it is dehumidified before entering the house.
the idea is to keep the house under a slight positive pressure so that it is not sucking through unsealed holes.

This is just the way that has evolved for me over the years
to address this situation.
Keep in mind that these homes were tested and amount of fresh air...and need for this added air..was verified
and not just based on home owner or builder assuming that
the structure was actually tight enough to require fresh air.

skuttle 216 is one example of a barometric damper.
install the set up described above..set the weight on the
damper..and forget about it..except for changing the filter
in the 12x12 fbg.

keep in mind that mine is a hot humid climate

best of luck.

My ERV is in the basement in a standalone configuration, and the inlet/outlet vent is at the back of the house about 9 feet up from the ground (ceiling joist level in the basement), shaded area most of the day.

OP seems on the fence about the ERV which is understandable. I would just plumb for the vent (or vents) during construction so you can easily add it in yourself later if you find you need it.

The ERV's aren't cheap. The Broan unit I installed was ~$1100 with all parts. If an HVAC contractor installed it it would have been a lot more. I have afreind who got a quote for 2500 for an after build install of an ERV - yikes! I also had to upgrade two of my tstats to IAQ Vision PROs and that wasn't cheap either.

The air vents are more reasonable but this approach is akin to opening a window. The only difference is that the vent "window" can be opened automatcially inconcert with the HVAC system running. I wouldn't go that route but the OP asked for info on it.