Open bedroom windows in a tight house
A general question. We are in the process of building an energy efficient house that will be tight and well insulated. My wife and I over the past 34 years have lived in Minnesota and now Montana. We have year around slept with a bedroom window open, including winter. I have been planning on having Panasonic bathroom fans regularly exhausting the house.
If we have bedroom windows open regularly and a regular plan to exhaust air out of the house, is that adequate in terms of air exchange? Obviously this is not as efficient as an ERV or HRV air exchanger but is it a reasonable plan understanding the lack of efficiency?
Thanks Montana Zone 6
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
If you run the fan without having a window open, your outside air is going to come from somewhere else and that may not be somewhere you want it to come from. To get around this, you could try a fresh air supply that hooks into your HVAC and turns on when the bath fan is run, such as AirCycler. It's a good bit less expensive than an HRV or ERV.
I moved from a lifetime of old houses into a new, tight house (0.5 ACH50). It's wonderful. But I know for certain it would be an abject disaster without my HRV--at least for the months I'm heating or cooling. Leaving efficiency issues aside is anathema to GBA, but we'll play along. I'll bet you could manually simulate the balanced effect of a well-designed, efficient ventilation system, but what about when you leave for a stretch, or when you're too tired to go adjust the dampers or open or close the window? If you're nerdy enough to want a tight house, adding efficient mechanical ventilation is the fun part not to be missed. You can do it on the cheap with the bottom end HRV;s. Even at 75% efficiency, they're still better than an open window or HVAC fresh air interlock.
Jay,
Here is a similar thread that might be worth reading. It's from a couple of years ago. I'd be interested to see if Martin still thinks an exhaust only system makes sense.
https://www.greenbuildingadvisor.com/community/forum/mechanicals/48106/ultra-inexpensive-balanced-ventilation
Jay (and Malcolm),
More and more experts (including Joe Lstiburek) are bad-mouthing exhaust-only ventilation systems and recommending balanced ventilation systems (HRVs), especially in cold climates. But the fact remains that many homeowners (particularly owners of small, compact homes) are perfectly satisfied with the performance of an exhaust-only ventilation system.
The main reason that exhaust-only systems are maligned is that they don't provide good ventilation to people when they are asleep, especially if they keep their bedroom doors closed. That problem does not apply to Jay and his wife, who are apparently willing to accept the energy hit associated with enjoying the pleasure of massive amounts of ventilation when they sleep.
Thanks Martin, that's been my experience here too. Our code allows them for single storey houses under 1800 sf.
Are you going to super insulate your master suite from the rest of the home?
Thanks all for the responses! We will be using mini-splits to heat and cool so no duct work. We hope to be tight close to 0.5 ACH50. We will probably end up putting in some passive air vents in the bedrooms, especially for the less occupied guest bedroom and see what happens with an open window or not. We have never lived in a tight, energy efficient house before, so new territory, but I expect my wife will want an open window at night. We do not plan on super insulating the master suite from the rest of the house.
Why do you keep windows open in a zone 6 winter? Have you had comfort issues with the previous houses or is it a habit without reason? I can't imagine the rational behind keeping windows open when it's 0f, snowing, and wind gusts of 40mph.
I live in a cold/snowy part of NH (zone 6) and our house is tight, under 0.5 ACH50. We went with a ventilation system of Panasonic bath fans and passive air inlets. With a house this tight, you will need multiple passive air inlets, the number depending on your house size and ventilation needs. This system has worked out OK for us, but it can get a bit dry during cold/sunny weather because of the unconditioned winter air coming in.
My advice (and I bet others who have built in similar situations would concur) would be to integrate a HRV into your build. This can be done to provide continuous ventilation and boost ventilation in bathrooms, so you could ditch the bath fans. It will also be less holes (flashing, trim/siding detailing) in your wall to deal with, only one supply and one exhaust hole.
The HRV is what makes the most sense. The open windows plan doesn't sound reasonable given you have time to develop a better plan.
Jay,
It is a lot easier to design-in a ventilation solution than to retrofit one down the road. Building to a passive house level of air tightness suggests you care about performance and comfort. Otherwise, why not save yourself a pile of money and build a code-minimum house?