More Q&A Spotlight
There used to be a joke in certain circles that the perfect house could be cooled by a can of beer and heated with a fart. We’re not there yet, but we’re trying. As we get better and better at building energy-efficient enclosures, we can heat and cool our homes with smaller, more affordable equipment. Innovations in minisplit heat pumps, for example, have made comfort somewhat more affordable. Often, single ductless units can be set up to handle homes with open floorplans, just like an old-fashioned AC window unit would take care of a single room. And ducted minisplit systems can be designed and installed to serve more-complex floor plans with the smaller capacity that low-load homes often need. A tighter enclosure does require balanced ventilation, though, and sometimes dehumidification—costs that often aren’t considered in your average American home. So the cost of HVAC continues to be a concern for anyone building or remodeling a home.
An example of this popped up in a recent Q&A post where GBA member “shawnbatt” tell us that he is designing a 1340-sq.-ft. ranch house in Climate Zone 5a. He estimates the heating load (the amount of energy required to condition the space) will be around 18kBU/hr. He wants to know if a centrally located ductless minisplit head can adequately provide his HVAC needs. If so, he’ll pair the minisplit with a fully ducted HRV for balanced ventilation, a partially ducted heat pump water heater (HPWH) for hot water, and even baseboard radiant heat in the bedrooms as a backup.
Shawn likes this plan because the house will not have a basement, and he won’t need to find ways to run more significant ductwork. He says that he’s generally OK with the idea of ducts…
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5 Comments
Not directly related to the topic, but this house plan desperately needs the input of an experienced designer or architect.
Malcom, just curious, what do you see as the biggest problems of that floor plan?
Also, I've found the Slow Home series on YouTube and the Not So Big House book helpful when it comes to floor plan design but I've had trouble finding other resources about the topic. Can you recommend any?
Thomas,
The circulation patterns, the relationship of the bedrooms to the common spaces, and that the living and dining room are sandwiched between service rooms and bedrooms so they don't have much exterior walls space connecting them to the outside. But more generally it feels like the space has been divided up with no theme nor governing idea as to what you are trying to achieve.
Design is something that takes experience and many iterations to get good at. The first house I designed wasn't as well thought out as the second, and so forth. It's worth getting professional help - or starting from an existing plan you can make minor modifications to.
Corbett Lunsford at Home Performance on YouTube would second the ERV instead of HRV and ducted instead of ductless recommendations. In this presentation he says he doesn't see any way around a duct system with particular attributes for a floor plan with any complexity.
https://www.youtube.com/watch?v=05S4lfY4v4A&t=2183s
At that time stamp he talks about the disadvantage of ductless minisplits.
At this time stamp he talks about the inevitability of ductwork.
https://www.youtube.com/watch?v=05S4lfY4v4A&t=2430s
Here's the slide of his duct system he recommends referenced in that video.
https://static1.squarespace.com/static/5535501de4b0b3c77cb11d63/t/659d77e2f52f9c244d6bef5c/1704818658167/BPW-PerformanceVentilationLayout-2024.pdf
In a cold climate ventilation air does not help even-out temperatures in a house heated by a ductless mini-split. This fallacy landed in our region with the arrival of Passive House and hasn't been fully shaken decades later. Even the best ERVs deliver air that is cooler than the house air. In a house that lacks direct heat delivery in some rooms this means the ERV is actively cooling off those spaces. In this small ranch that would have meant chilly bedrooms. As some have pointed out, the tolerance for bedrooms cooler than the rest of the house varies widely. As a designer the best approach is to create spaces where the conditions can be controlled to the occupants' liking. And a ductless mini-split ain't it.
Panasonic has a hybrid solution to the issues raised by shawnbatt, although it's not evident it's suitable for a small house like this. The Panasonic Oasys system uses a utility room as a plenum, dumping fresh air, heated/cooled air, dehumidified air and filtered air into one space from which conditioned air is distributed to the rest of the house. It's a bonkers solution, but does solve a lot of problems associated with high performance homes, including allowing small ducts!
Speaking of small ducts, have recently worked on a bunch of homes using the Rheia duct system. This approach uses us pressurized plenum and small diameter home run flex ducts to each space. The smallest ducts fit in a 3.5" cavity. Final performance testing next week, so can't yet fully endorse, but you can get a whole home duct design from the manufacturer and that's a far cry better than no duct design at all.
As for the water heater, the latest crop of heat pump water heaters are blessedly quieter than those from just 5 years ago. Select a quiet model and duct both sides to a space where noise won't be a problem: mudroom, hallway, even the kitchen. But now we're talking even more ductwork, so best to just locate the water heater in one of those noise-tolerant spaces. The entry from the garage is the best candidate.
Good luck, shawnbatt. Hard decisions ahead. It goes without saying, good design is always worth it.
https://oasys.na.panasonic.com/
https://rheiacomfort.com/
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