Minisplits, Air Handlers, and a GTFO Approach to IAQ (Building Resilience Episode 5)

Mechanical equipment that is tuned to the space it must condition: a small air handler and ceiling-mounted mini-splits

October 20, 2022

Last time on Building Resilience, we were cutting styrofoam, gluing the back, and sticking it to the walls in two crawlspaces, where we had already plopped it on the floor.

That’s when we broke out the froth packs.

"Spray foam insulation. It’s a big part of how we build today, it’s one of the key ingredients in our building type.
Dupont happens to make something called Froth-Pak, which is kind of a more portable version if you don’t need to necessarily foam an entire house, you got some smaller areas that you need to address.
Comes in a red version and a green version in a variety of different sizes. What you need to know is green is for air sealing and red is fire rated.
And I don’t care how much you think you know about spray foam, always stop and read the instructions before you use any chemical product like this. It’s not hard to use, but it’s really important that you use it properly, safely, and it’s got some very specific steps that it walks you through before you use it."
— Michael Anschel

This week, we’re going to dig a little deeper into the mechanical systems that provide heating and cooling to each part of the house.

"So, heating and cooling systems. This house has a boiler which means that we’ve got radiators throughout the house that are providing really great heat.
We’ve got in-floor, we’ve got standard cast iron all over. But cooling is something that these old houses didn’t come with. Now upstairs in the attic, where we foamed the whole lid and made this whole thing super super super tight, we were able to put in an air handler and what we might think of as a traditional forced air cooling system that’s providing cooling to the second floor.
Very short duct runs, easy to do, easy to balance. And because our BTU load overall went down, we’re able to put a fairly small air handler from Mitsubishi up there.
Now when it comes to the first floor, we don’t really have a great way to bring enough ductwork down to the first floor to provide cooling.
Moreover, I don’t particularly like ductwork. It usually gets pretty gross in there, people don’t clean it as often as they should, and so the other way to bring cooling into a house is with mini-splits.
But when you say mini-splits, oftentimes people’s first reaction is kind of like ugh. They don’t like the wall wart, they don’t like the thing that sits on the wall.
And Mitsubishi came up with a really, really brilliant system for us to bring mini-split cooling into a space without having the thing on the wall that people object to. It’s actually right above me. In the ceiling, we have a ceiling cassette. Now this is a traditional mini-split, in the way that we would normally think of it.
Except that the only thing that we’re going to see is a white grill on the ceiling like a ceiling fan or something else. Other benefit of putting it here in the kitchen is I’m got some south facing and I’ve got some west facing glass, so this is going to be a really warm space.
And it’s, in terms of comfort, how the person reacts to the space, this is going to provide cooling where we need it and want it most."

Mini-splits are an air conditioning system that can provide heating and cooling

Mini-split air-source heat pumps can provide heating or cooling where it’s needed, rather than where it’s needed as well as where it’s not needed.

In the kitchen, a ceiling-mounted unit provides cooling, and in the renovated basement another one provides heating and cooling. The hyper heat technology of Mitsubishi mini-splits means they work well in very cold climates like Minneapolis.

Both mini-splits can be controlled from your phone with an app, or with a remote control contraption that is much harder to lose.

PLAN OF ATTACK: Encapsulate the attic with spray polyurethane foam

An air handler in the attic provides cool air to the upstairs of the house. 100 years ago when the house was built, very little insulation was used.

Even when they did begin insulating attics, it was in the attic floor and it was usually inadequate. Air conditioning equipment that was added in the 80s and 90s was added above the insulation, putting the AC unit outside the house.

To tighten the shell and to place the mechanical equipment inside the thermal envelope of the house, we’re going to use spray foam on the underside of the roof deck.

The attic is the hottest part of the house during summer, so it's critical to get the air handler out of the heat and into the house. Downstairs, the Mitsubishi units are great for remodeling because they slip between 16-inch on-center framing, which happens to be the way this house was built.

The cover plate is left off until the drywall goes up, so the guts of the unit are protected with a temporary cover.

Refrigerant and condensate lines from inside the unit can snake through the framing through ceilings, walls, and floors on their way outside to the outside compressor unit, where excess warm or cool air is dumped.

As long as we are out here looking at mechanical stuff, let’s look at the white PVC pipe running up the side of the house.

That’s a radon mitigation system sucking soil gasses from under the basement slab up out and away.

How to keep the inside in and the outside out

Okay, we’re going to jump into the Wayback machine and look at the “before” scenario for this attic. We climbed up there in late June, and it was warm.

"Whoo. It’s warm up here. This is nice, we’ve got our refrigerant line just dangling here, looks like someone tried to use duct tape to hold it together. And we’ve got, man, we’ve got our air handler here up in this hot attic. Insulation on the floor is kind of iffy. Some mouse droppings and whatnot.
We’re going to change this whole condition. We’re going to put R-50 on the roofline, we’re going to bring all the ductwork and the mechanicals inside the conditioned space, get a new air handler up here that’ll be tied to condenser that’s also running a couple of our mini-splits below.
And ultimately this fairly awkward, hot, uncomfortable space is going to become super comfortable and the house’s overall efficiency is going to jump—pretty dramatically."

Another tricky space in the house is the sunroom. It’s heated with a classic radiator, which will be fed by a high-efficiency boiler, and these single-pane windows will be replaced with energy-efficient windows.

But even with a low solar heat gain coefficient, this room is likely to need cooling in order to live up to its full potential.

So we’re going to put one of Mitsubishi’s EZ Fit ceiling cassettes into the ceiling, running the condensate and refrigerated lines down the wall, across the floor system, and out the house to the condenser unit.

And speaking of getting out of the house, a big piece of IAQ is GTFO — Or getting pollutants out of the living space.

One of the existing pollutants in need of a GTFO IAQ improvement: is carbon monoxide. Which comes from atmospherically-vented combustion appliances, like this water heater.

"We’re going to talk about mechanical equipment a little bit. It’s at the heart of the home, it’s providing the heat for the house, the hot water for the house.
And this in and of itself is a finely made piece of equipment, except for one major problem and that is it’s atmospherically venting. And yes technically they’re legal, but they probably shouldn't be.
What we want to do is make sure that any appliance that we have like this that is burning flue gas isn’t relying on an atmospherically venting method of exhausting that gas from the house.
So we’re going to talk about sealed combustion, so it’s not using occupant air for the fuel. And direct vent for our appliances so the air that these things use, we want it to be separate from the air that these things use."

And that’s not just a bunch of hot air. IAQ is a BFD in tight houses, and mechanical systems can work much more efficiently and as intended when they’re part of a finely designed system.

And speaking of a finely designed system, Next week we’re going to peek into the water and air control systems on these exterior walls.

We’ll install a new peel and stick Weather Resistive Barrier from Benjamin Obdyke and a tried and true invisible WRB to back up the open cladding system from AZEK.

And all of that comes next time, on Building Resilience.