Comments on: Building Enclosures vs. Mechanical Systems

By: Shae

Shae — Tue, 06 Sep 2022 14:21:49 +0000

Good article but I wish I had more juicy details. Where can I find out more about how much I can save monthly? Which style unit should I pick? Single, 2 stage, modulating?
I am in the midst of picking out a new HVAC unit. I need to get more quotes though. I have a few question about units and ROI. I have air sealed my home pretty well but still more to do. I have added some attic unsulation (need more), sealed half of my rim joist (more need to be done but its behind drywall)and air sealed most of the attic. I need to get new windows, current ones are single pane. My old HP went out this week which was a 3 ton nordyne unit. Duct work in unconditioned attic and was feeding the main floor of 1128sqft with 1 7-8″ flex run to the basement attached to 1 register. That was ok for the summer but usesless during the winter. My power consumption is 24,000KWh a year at 0.12 cent per KW. Full electric. How can I determine if a “cold climate HP” is going to be worth it???

Plan is a minisplit for the basement but I dont think its in the budget to put ducts in conditioned space. This hopefully wont be our last house but who knows how long we will be here.

By: RoyC

RoyC — Wed, 31 Aug 2022 13:38:18 +0000

In reply to Allison Bailes.

When I was a builder, we used double 2×12’s with 1/2″ spacers for headers regardless of the width of the opening. This was just for convenience. But in hindsight, we should have used single headers wherever possible so that we could have 2″ of good insulation instead of 1/2″ or none.

By: Patrick Huelman

Patrick Huelman — Tue, 30 Aug 2022 21:14:47 +0000

It is a two way street. Clearly the enclosure has a huge impact on HVAC design, sizing, and performance. But HVAC systems — especially when improperly designed, sized, installed, and operated — can create significant impacts on the enclosure, too. Poor ventilation and dehumidification can cause unintended internal moisture loads on the enclosure. Improper balancing of heating/cooling or ventilation systems can cause significant positive or negative pressures that can challenge the enclosure.

By: LeeH

LeeH — Tue, 30 Aug 2022 21:04:16 +0000

In reply to Robert Danielson. Sounds like a good experiment for me to try this winter. I'm not super insulated but I would say I'm better than "pretty good". It'll be easy to pick a day, turn off the heat and watch the temperature drop. Last winter we were away for three weeks and I only left the center zone of my three zone Fujitsu operating. It was set at 65F, the lowest the tstat allows. I had thermometers in the bathrooms at the farthest points from the center zone. The temperature never dropped below 60F in either room and about 58F in the basement where there was no heat.

By: Robert Danielson

Robert Danielson — Tue, 30 Aug 2022 19:27:50 +0000

A clarification on my first comment : What can or does happen inside a very well insulated home if the mechanical heating and/or ventilation systems are off-line and the home is occupied during cold weather ?

By: Allison Bailes

Allison Bailes — Tue, 30 Aug 2022 19:17:04 +0000

In reply to george penick.

george: It depends. You mention headers, so are you asking just about using spray foam instead of board foam in the headers? That’s difficult to do, especially in 2×4 walls, which are the norm in warm climates. If you’re talking about other parts of the enclosure, how much spray foam are you installing? How well is it installed? I’ve seen some poorly done spray foam jobs, so it’s definitely not a panacea.

By: Allison Bailes

Allison Bailes — Tue, 30 Aug 2022 19:14:09 +0000

In reply to Robert Danielson. Robert: I discussed this a little in the article below. See the part about the Passivhaus challenge. Heat Pumps, Auxiliary Heat, and Resilience

By: Allison Bailes

Allison Bailes — Tue, 30 Aug 2022 19:11:33 +0000

In reply to RoyC. Roy: Yes, I was talking about basement slabs, mostly. I've seen some slab-on-grade foundations in cold climates, but they aren't common. And yeah, the same comment about one chance applies to other climates as well, but insulating beneath a slab in a warm climate usually isn't worth the trouble. Slab-edge insulation can help, but you have to be careful in termite territory.

By: RoyC

RoyC — Tue, 30 Aug 2022 19:09:13 +0000

This sure brings back memories. I started my career in the late 70’s and saw a lot of new ideas like passive solar with Trombe walls and earth-bermed houses. All of these concepts were either not cost effective or resulted in large indoor temperature swings. Active thermal solar collectors also gained popularity in those days, but failed due to poor system designs and lack of maintenance. I agree that well-insulated, tight homes with good windows are better solutions. If they become widespread, perhaps we will develop better HVAC systems to go with them.

By: RoyC

RoyC — Tue, 30 Aug 2022 18:43:42 +0000

Allison, I don’t understand this comment:

“And if you’re in a cold climate, you pretty much get only one chance to put insulation under the slab.”

Who builds on a slab in a cold climate? Are you talking about the slab in the basement? What about slabs in warm climates where they are common ?