Community: Mechanicals

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7 Answers

For a superinsulated house being extensively retrofitted in South Jersey (R-40 walls, R-70 attic, triple pane windows) with a permanently wet crawlspace (riverfront, high water table), I am considering positioning the exhaust duct from the Fantech heat recovery ventilation system to expel over the top of a hybrid heat pump hot water heater. The HWH will be in the insulated unheated 2 car garage, possibly next to a geothermal water-to-air heat pump. I would plan on turning that exhaust vent away from the HWH in summer.

Asked By Michael Arnold | Jan 22 13
3 Answers

We are going to have a Mitsubishi heat pump installed in our house (in progress) soon and would be interested in some thoughts on sizing.

The house is in Jackson, NH 03846 (climate zone 6a). It's cold and snowy, but we have great passive solar gain, open floor plan, tight construction, and high insulation values. We have wiring in place for regular electric resistance backup. Our Energy Star rater calculated our heat load at 11.2kBTU / hr at design temp (-6F, 65F inside, based on St Johnsbury VT).

Looking at the new Mitsubishi FH line, MSZ/MUZ units:

Asked By Brian Post | May 23 14
14 Answers

I read an article by Martin Holladay who said ERV could actually make the situation worse in hot humid climate during those days when temp and humidity level are mild. That confused me. I would appreciate answers to questions about the best vent. system for a new build air tight house at approx. 2200 sq ft, in zone 3A below the red line. Heat pump HVAC system.
1. Why might an ERV make matters worse on mild days with low humidity?

Asked By rob clark | May 23 14
51 Answers

In another thread, my choice for HVAC was appropriately questioned. The system seems inordinately complex, costly, and convoluted. At least, on the surface. But digging deeper, the reasoning behind the design becomes clear. But, does that make it right? Is this the best HVAC design, or is it redundant and wasteful?

Here are the pertinents:
• Climate Zone 6
• 2700 sq. ft. finished space in story-and-a-half (bungalow style) house
• 2000 sq. ft. unfinished basement (future completion for aging parents)
• 4 Bdrm, 3 ½ bath house
• Tight, highly insulated home

Asked By Kent Jeffery | Apr 16 14
1 Answer

I asked an earlier question about how to deal with my existing central heat and no a/c system. Based on the responses, I'm planning to repair the ducting system some. However, I still need a cooling solution and doubt that I can effectively centrally cool the house due to the vertical split level nature of it. I already know that 1/2 of my cooling load is in rooms that effectively don't have central ducting.

So I'm looking at using either a multi head mini split to cool the house or multiple single head units. I'll probably get at least one heat pump unit so I have that option.

Asked By Keith H | May 6 14
8 Answers

Hi everyone!
I am finally getting ready to dig and got back my system sizing and I have a few questions as it seems over sized and what homes normally receive without this amount of insulation and product.
What first led me to believe something looked off was that my heating load was higher than my cooling as well as the sqft area of the rooms were not looking correct.

If you wouldn't mind taking a quick look and helping me understand if it seems correct or that I should have a conversation with the individual that I paid to size my system and perform the duct work design.

Asked By Matt Anderson | Apr 30 14
4 Answers

I had a Manual J performed recently and also did one myself with .

A few questions arose that I didn't have good answers to. Some of these questions might help other people doing a Manual J in the future.


  • Should the truss/joist space be included in the height of a room? I personally assumed yes if the truss was in the conditioned space but no if it was behind a good air barrier (roof, etc).

Asked By Keith H | Apr 29 14
5 Answers

Hi all,

I'm performing some repairs on my house and discovered that most of the central heating duct work was poorly executed and needs rework Or does it?

I have a fundamental question to decide that I think the GBA community could help me with:
- Should I repair the central heating system
- Should I largely abandon it for mini splits?

House Basics:
- 1976 split level (~6 elevations)
- Climate 5b
- Low slope black epdm roof (relevant to cooling)
- Furnace: 95% 2 stage ECM variable. 75k/115k btu. Fan rated 1100 to 2000 cfm.

Asked By Keith H | Apr 29 14
2 Answers


Does anyone have a recommendation for crawlspace exhaust fans?

Would an appropriately sized Panasonic be the simplest option?

Asked By Jill Neubauer Architects | Apr 21 14
4 Answers

I've been reading a lot about minisplits on here and their virtues for heating and cooling homes. I currently rent a 500 square foot storefront on the ground level of a 3 storey brick commercial building. The climate zone is 5B. The only heat is electric baseboard plus a space heater in the back workshop area. This winter I was paying $300 per month to heat the small space and with the heaters full out, it was still 15 degrees (celsius) in here.

Asked By Jonathan Dalton | Apr 25 14
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