Exhaust-Only vs. ERV System Ventilation in Bathroom
I am looking at adding bathroom ventilation to a house that was built in the 1970s.
The house has a pretty standard envelope for a house of that time with fiberglass batts in the walls and blown-in insulation in an unconditioned attic.
My question is given what I assume is a fairly leaky envelope, does it make sense to go with an ERV style of ventilation system or just use something like Fantech’s PBW 110 Bath Fan w/Grill – Bathroom fans – Fantech ?
The house is 2300sqft w/ 2.5 bathrooms
Bath 1 – 850 cubic ft
Bath 2 – 560 cubic ft
Bath 3 (half bath) – 185 cubic ft
Obviously, we are talking about two different price points. I am having a hard time determining if an ERV system is a worthwhile investment given the envelope, but 110cfm of exhaust only seems like a fair amount to pull through random leaks in the house.
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As I understand it, an ERV system is only needed in a tightly insulated house, so that you can supply fresh outside air, and exhaust stale inside air, all while minimizing the effect of introducing cold/hot/humid/dry outside into your house.
The 1970's house doesn't need any extra ventilation, as it should get plenty through the air leaks all around it's building envelope. The only time you would go with an ERV for that type of house is if you are remodeling, and spray foaming, or otherwise tightly insulating it.
Unless the above is true, then just put in normal bathroom fans, since they aren't running all day, just 30 minutes to an hour at a time. Definitely put in a timer for them all, so that they aren't left running. That's what we did for our 1960 era brick house. Didn't notice any issues in the house when we ran the bathroom fans, whether it was cold or warm outside. I did put the timers on, because if you don't, your kids or spouse or guests will leave the fan on all day.
I would say it depends. Disclaimer: I'm not an HVAC engineer, just some asshole on the internet.
No HRVs/ERVs are not ONLY for tight houses. Consider that the 'ventilation' though the walls of the assumed leaky assemblies is going to be passing through dust, mold, crap etc. and may be airflow restricted (ie: not pushing out its full capacity)
A mechanical ventilation system that brings in as much air as its sucking out, being net neutral in pressure. Consider even making it slightly positive to bring in better controlled ventilation air and it'll push out the leaks in the walls. Also, now you're bringing in filtered air (although the standard filters in many ERV's aren't much, but you can upgrade them or put in a filter box) which I consider a much better system for indoor air quality.
If its only for the bathrooms, consider an HRV so you can better exhaust high moisture air, as opposed to keeping most of that moisture with an ERV. This highly depends on where you are in the world and what the exterior air moisture content is throughout the year. Moisture is a big issue, track it and make sure its good.
Also, there are huge price differences for performance, most people would just put in three $60 bath fans from home depot and call it a day. if you want better indoor air quality, and HRV is going to cost significantly more . its up to you if its worth it.
I am just north of Dallas, so climate zone 3A W/H.
I was looking at the Aldes IAQ system for 2.5 bath and you pretty quickly hit the $1100 mark, so some rational starts to be required when you jump from the $60 Home Depot fans to that price bracket.
I'm not trying to be patronizing or an a**hole...but the reason why HRV/EVR's exist is to address the bad air problem inside the extremely tight houses that are built today. I would hesitate to apply a solution that is absolutely necessary for the tight houses, to a leaky house, as the issues are completely different.
A leaky house has sufficient or more than sufficient ventilation. Putting an HRV/ERV into the equation just doesn't make sense to me, unless you also make the house tight.
If you go the positive pressure route, then during winter, warm moist air will be seeping into your wall cavities if your house is in the Northern states. You may see wood rot and mold if that happens. And during summer, you will be pushing cool air into your walls, and losing efficiency also. There is a reason why HVAC installers are supposed to balance their furnace/AC installs to not have positive or negative pressure.
I think the best you can hope to accomplish with a HRV in a leaky house (which you don't make tight) is to not draw more air than is already coming in, and keep your balance neutral. And allow the leaky air to continue coming in as before. It's not an unreasonable goal, but the cost seems high for the benefits. And you would need to have the HRV in on-demand mode, only turning on when the bathroom vents (or kitchen vent) is on, and then shutting off.
Personally, I would not bother with an HRV/ERV, but instead would go the bathroom vent route, and properly vent it outside, it will work perfectly fine. If the 1970's house and occupants survived just fine until now with leaky walls, I don't think an occasional fan will cause any issue when it draws a bit more air through for temporary periods of time. That's how they were designed to work. And in reality, the air coming in IS cleaner than what's in your house, especially in the bathroom or when cooking.
There is also the matter of climate. Are you in a cold climate? I ask because, as Martin points out in this article, the high cost of an ERV or HRV system can be justified in very cold climates, but in milder climates where the energy penalty incurred by simpler ventilation equipment is lower than it would be in a cold climate, it might be best to install less expensive exhaust-only (in your case) ventilation equipment.