Ventilation choices for new home
I am remodeling to the point where it is essentially a new house. I am putting in spray-foam insulation, and we are fresh air ‘nuts’, so I want mechanical ventilation. I’d also like to be as green as is feasible.
We got a quote for HVAC from a very reputable local establishment. The person who did the quote sems to really ‘get’ green heating/cooling and the effects of spray-foam insulation. However, there’s a whole lot of optional components in the bid and I’m having trouble figuring out what I must have and what I can live without. Any help with this would be most appreciated.
The house will be 2300 sq. ft of living space, and we are in San Jose, California, so our conditions are quite mild in the winter and only sometimes horribly hot in the summer.
First off, they spec’ed a Honeywell ERV. That surprised me, I would have thought that an HRV would be more appropriate in this dry California climate. Any thoughts on this choice?
Then the rest of the optional items: First, an ASHRAE 62.2 continuous ventilaion with positive presure using Aprilaire model#8826 ventilation control. I believe they said that this would help with the air removed from the house by bathroom and kitchen exhaust fans. Then, a “free cooling” unit upgrade which would upgrade the thermostat to have a programmable continuous fan. This would provide 55 CFM continuous fresh air and 400CFM free cooling (I believe this is for fresh air in the evening and nighttime in the summer so you can turn off the AC). And lastly there’s an AprilAire air cleaner. All this on top of the ERV.
Do I need all of this? I do like the idea of the free cooling (we used to have an all house fan which we liked, but we’re looking for a way to be able to leave the windows closed because of security and noise reasons). Do I really need the 8826 on top of all this other stuff? What happens if I don’t get it?
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The Aprilaire model#8826 ventilation control apparently will provide makeup air for your kitchen hood which likely sucks quite a bit if it's anything like what most people put in who are doing a remodel as extensive as your own. A means to provide makeup air is required but as an alternative to this mechanical system, you just can open a window when you vent from the hood. As far as your bathroom exhaust, that should be balanced through the ERV which should be connected to the bathrooms, so as I see it, the #8826 should be to balance the kitchen only. Whole house air cleaners are amazing and I highly recommend. They are usually placed in line within the system so that any air coming from outside to inside goes through a HEPA filter. If you do the recommended system in it's entirety, make sure the kitchen makup air also goes through the air cleaner.
I'm a general contractor who has designed many of these systems but I defer to an HVAC person for expertise. I would discuss this with him/her. Ask for a diagram of how this is to work. If they're anything how I've learned to be they may not get too detailed though. Providing valuable plans and diagrams to someone who ends up diy on the project or who gives them to a low cost and low expertise installer can be risky for the legitimate contractor.
Sorry, as far as the free cooling upgrade is concerned, I'm unclear on what this really is. If there is another fan involved (since a ERV is usually not designed to move 400cfm), I guess this is just a whole house fan. You need to open a window for this to work at 400 cfm or rig it with another #8826 which could be tricky (they would have to go on simultaneously and be balanced). The 55cfs seems to be what the ERV is designed to do as a part of its normal functioning. If this is just a thermostat upgrade which integrates a ERV and Whole house fan, it may be worth the cost. Controls are very important for such a system to work as it should. This could also be just a single ERV (sans whf) with a control that has a 400cf high power capability for quick venting a bathroom after a shower and such. Seems a bit powerful though. Ask the contractor.
Pia, be advised that spray foam could be counterproductive to your goal of pristine air quality. See this thread for example: https://www.greenbuildingadvisor.com/community/forum/green-products-and-materials/14537/out-gassing-bad-stuff-spray-foam-insulation.
Basically the commonly used two-part spray foams can result in chemical odors when improperly mixed or when installed at the wrong temperature. Of course this is not always the result and there are many happy customers, but also a handful of nightmare stories as in the link above. There are insulation options that do not carry this risk, for example cotton batts or cellulose.
Pia,
I think we need more information.
Concerning the ERV: either an HRV or an ERV should work fine to provide whole-house ventilation, as long as the contractor uses the ERV fan (or HRV fan) for distribution, rather than depending on a furnace fan or air handler fan, which can waste a lot of electricity. You might want to read HRV or ERV?
I was unable to locate online information on the "Aprilaire model#8826 ventilation control." Mark Obmf suggests that the control will be used to open a motorized damper to introduce makeup air for your range hood fan; if that's the purpose, it probably makes sense.
I'm also uncertain what you mean by a "free cooling" unit. If it is actually a 400-cfm whole-house fan, then it has nothing to do with ventilation; it simply provides nighttime cooling. As long as you know how to use it, a whole-house fan can make sense.
Most homeowners are happy without a separate air cleaner. However, if you have family members with special medical issues, or if you live somewhere with bad outdoor air quality, the air cleaner may make sense.
Martin,
I am not familiar with many of the terms that are used regarding HVAC equipment and such. Does the site have a place that gives discription? There seems to be a lot of different equipment out there and if you aren't up on it, some of the conversation is difficult (at least for me) to understand fully.
Thanks
Roy,
Many technical terms used at the GBA Web site are defined in our Glossary. Here is a link to the Glossary: Click here.
You will also notice that every GBA page has a link to the Glossary at the top upper right of each page. The word "Glossary" is in black, between the words "My GBA" and "Store."
For more information on mechanical ventilation systems, I recommend these pages:
Designing a Good Ventilation System.
GBA Encyclopedia: Ventilation Choices.