Split System Heat Pump

LESLIE: Chris in Alaska, you’ve got The Money Pit. How can we help you today?

CHRIS: I’m removing a dropped ceiling from my kitchen and I ran into a vent pipe from my forced-air heating. And I want to move it into the joist and I’m wondering if I can cut a hole in my joist to run it; my floor joist from the second floor.

TOM: Alright. So you have to cut through a floor joist to be able to run this vent? So if you’re going to cut out a floor joist, you have to reinforce it.

CHRIS: Well, wait. OK.

TOM: The floor joist is supporting the second story and whenever you cut a hole in a floor joist, you basically are eliminating one floor joist because you’re essentially cutting it in half.

CHRIS: Sure.

TOM: What you’re supposed to do is double the floor joists that are opposite that and then bridge across between them. So if you cut out, say, a 1-foot chunk to run this pipe, you would have to double the 2 floor joists that are at opposite sides of that. And then you run another, say, 2×10 in between those, perpendicular across the cut opening. So you’re essentially framing out an opening as if it was a stairwell or something. So it’s a big project, is what I’m saying.

CHRIS: I have a 6-inch vent pipe going through a 2×10 and I’ve got to go through three 2x10s. So I suppose I would just bring up …

TOM: Ah, wow. That’s a big – yeah. A 6-inch vent pipe. That’s a – you’re taking a lot of strength out of the floor. Isn’t there other way – any other way we can do this?

CHRIS: Unfortunately, no. The vent pipe runs along the joists for quite a distance and then it goes down into where the dropped ceiling was, travels across three joists and then back up in between the joists and then up to a bedroom that’s on the second floor.

TOM: This vent pipe is for what?

CHRIS: It’s a forced-air heating duct.

TOM: And in where is the ceiling? Is the ceiling in a – over a kitchen?

CHRIS: It is.

TOM: Is there a soffit above the cabinet that you can run this duct through?

CHRIS: No. I’m actually trying – there was a dropped ceiling and I’m removing all of that to try to increase, you know …

TOM: Typically, you don’t go through the floor joists like that; you go under them and you box it out.

CHRIS: OK, OK.

TOM: I would not cut 6 inches out of three 2×10 floor joists; that’s too much to take out of the floor joists.

CHRIS: What about using metal plates to sister it?

TOM: No. Not enough strength.

LESLIE: And there’s no way to bring this duct up onto the floor surface and just sort of build like a small surround that would be like a little ledge or …?

TOM: No. You would run it underneath the floor joists and you would box it in.

CHRIS: Right, right.

TOM: Is it possible that you could add a second heating system to this room, like a through-the-wall system?

CHRIS: I could do that. I could block off the pipe and add its own heating system to the room. It just seems extraneous, I guess.

TOM: Right. Well, you could use a through-the-wall – you could use like a split-system heat pump, for example, and get cooling and air conditioning through one mini-split, ductless system. So you have a small compressor outside, then you have the air handler attached to the wall and that becomes both a unit that will supply heating and cooling. Take a look at the units by Mitsubishi. They’re set up for situations like this.

CHRIS: OK.

TOM: Because the way you’re describing this run of the duct, I’m also concerned that you’re not going to have enough airflow to properly heat it.

LESLIE: To get the heat there when you need it.

The split system, of course, is going to be electric then, right, Tom?

TOM: Yes, it’ll be electric. It’s 240 volts.

LESLIE: So there’s a cost issue to worry about with that. But we have a split system in our home, in the basement, and it’s a truly fantastic way to heat and cool a space that’s just difficult to get heating and cooling to. But heating costs – especially in Alaska, I imagine, with electric – are going to be pretty expensive.

CHRIS: Yeah. We generally don’t need to cool.

LESLIE: True.

TOM: Well, that’s true. But the tip with the heat pump is set it and forget it.

CHRIS: Right.

TOM: You don’t want to bounce the heat up and down because then you force it into electric-heating mode. If you just set the thermostat and walk away, then the heat pump does the work.

LESLIE: And it really does a fantastic job.

TOM: Mm-hmm. Yeah. Because I’m afraid with the run that you just described for that duct, you’re just not going to have enough airflow left to do the job by the time you’re all finished. I mean a 6-inch duct is a …

CHRIS: Well, it currently runs to that bedroom now, so it runs that distance now.

TOM: Yeah. But listen, every time you put a twist in a duct, that’s equal to adding 20 feet of straight run. One corner – one elbow – is equal to 20 additional feet in terms of the resistance.

CHRIS: Well, then, I guess the way it runs right now, it runs along the joist and then it makes a 90 down and then a 90 to the right and it goes – it crosses three joists and then it makes two 90s to go back.

TOM: Wow.

CHRIS: And I’m actually – I’m going to get rid of two 90s if I go through the joists.

TOM: Right.

CHRIS: Now, the want that I had was – is there any way – what about reducing the pipe diameter to make a normal penetration in the joist; a normal (inaudible at 0:06:48) penetration in the joist?

TOM: What do you mean reducing the pipe diameter? Using a smaller duct?

CHRIS: Yeah. Right now, the duct is a 6-inch duct and reducing it to a 2-inch, running it through the – penetrating …

TOM: No. No, again, you face the chance that you’re not going to have enough HVAC power to heat that house.

CHRIS: OK.

TOM: You will not be delivering enough warm air to overcome the drop in temperatures in Alaska to heat that room.

CHRIS: OK.

TOM: And what if you got this all done and everything put back together and the first few, cold nights you’re miserable?

CHRIS: Right.

LESLIE: The first of many cold nights.

TOM: Exactly.

CHRIS: It’s a …

TOM: So, I hope that helps put it into perspective for you but I think a split system is probably a good option.