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1 Answer

Calculating break-even point when mini-split costs same as running boiler

I have original steam boiler that is maybe 75% efficient (it is converted to gas 10-year old boiler). Recently, because we wanted AC, we installed air-source heat pumps (Mitsubishi MXZ-2B20NA with MSZ-GE06NA and MSZ-GE09NA head units). Basically one heat pump has one 6K and one 9K heads.

I am located in Boston. COP of Mitsu I calculated at 2.6 since HSPF is 8.9.

So what I am struggling to figure out is at which outdoor temperature it makes sense to switch from boiler, that costs $1.5 per therm at current New England prices, to mini-splits at current $0.243 per KWh.

Asked By Apollo S | Mar 2 15

11 Answers

Do screws through exterior insulation reduce the wall R-value?

I was in a Net Zero Building class this weekend and there was mention that screws that are used to attached exterior insulation reduce the whole wall R-value by 39%.

The screws are attached from the outside thru the rainscreen, insulation, WRB, sheathing and into the framing.

This individual referred to an article from Energy Design Update (no issue was noted). I'd check but $600.00 for a subscription is too rich for my pockets.....

Any help here on the article or data at least, with other references?

Asked By brad hardie | Mar 1 15

5 Answers

Trombe wall (non-vented) with exterior moveable mode of insulation?

I am in the process of completing my energy efficient house design. Approximately 80% of the Building Envelope will be a Double Stud Wall Construction allowing for roughly 11" of Cellulose Insulation in addition to a 1" Rigid Insulation outboard of the Sheathing and inboard of the Hardie Cement Fiberboard Skin. The Remaining 20% of the Envelope will be Double Glazed Fiberglas Windows with emphasis placed on the South Elevation (Perhaps 60% on South, and 20% each on East and West). However, on the South Elevation I also have two sections of Trombe Wall - each 8' in width and 12' in height.

Asked By Thomas Tricarico | Mar 1 15

8 Answers

What is the correct climate zone?

Can anyone point to a web site that will be zip code specific to determine which climate zone you are located? The Department of Energy web site leaves something to be desired. I cannot determine a clear explanation of climate zone 4 and 4 Marine. It seems there should be a site to enter zip code or address and get definitive information regarding climate zone.
Thanks,
William

Asked By william dempsey | Mar 1 15

1 Answer

Should engineered wood flooring be glued to a concrete slab?

The builder wants to glue engineered wood flooring onto a new concrete floor, over a primer. Is this wise?

Asked By Christina Griffin | Mar 2 15

6 Answers

Biggest bang for your buck?

We are about to begin construction of a new home near coastal Connecticut. We are trying to incorporate green approaches where feasible. Three main components are: Insulation; energy source (ie Geothermal); and energy distribution (ie in-floor radiant heat or forced air). Of these three green approaches, how would you rank them in terms of biggest bang for yurt buck, assuming you can't afford all three. Thanks!

Asked By Justin Murphy | Mar 1 15

9 Answers

Adding wall R-value in a historic retrofit

What options are available for adding r-value to a wall if we can't remove the exterior siding? I see three options...
1) dense pack cellulose in the existing 4" wall cavities (~R 14-16)
2) Closed cell spray foam in existing 4" cavity (~R 26-28)
3) Add a double interior wall filled with 7.5" of dense pack cellulose (~R 26-28)

Asked By alok khuntia | Feb 28 15

14 Answers

Insulating a low-slope EPDM roof from the ceiling below

Hi. I recently had an Epdm roof installed on my 140 year old house. It's low slope and meets with a gable roof on the other part of the house. The Gable is standing seam. We had a tapered ISO board system installed as the underlayment to help with drainage and make the edge details easier to deal with. I reframed the roof and sheathed it myself before the roofing contractors started so I could save money. At the time the ceilings underneath the roof were all closed so I installed 4 inch rockwool batts right on top of the plaster/lath of the ceilings below.

Asked By joseph moore | Feb 26 15

9 Answers

Why is it so trendy to hate on radiant in-floor heat?

I recently built a 2000 square foot house in climate zone 7. The building is two stories on a slab heated by a Navien 240a combination boiler. There is no heat source on the second story, and the simple system has only one zone, which is all it needs because all the rooms in the house stay at the same temperature--maybe it's a few degrees cooler in the upstairs bedrooms if the doors are shut for 24 hours or more. I spent just over five grand on the heating system--installed--although I got a tankless water heater in the process, so the real cost was more like $3500. How is that overkill?

Asked By Josh Jipson | Mar 1 15

17 Answers

Recommendation for minisplits vs. gas-fired HVAC for new Massachusetts building

I am building an energy efficient 15 unit apartment building in MA this spring. We can either go natural gas or electric. I am considering going all electric since the MA Energy Code is so stringent and the heat load will be relatively small even though there are very cold temps at times. We might even put on solar panels for the house meter.
The electric units would take up much less space and I would rather not have to put in gas at all. I am not thrilled about electric hot water heaters but understand that the newer tankless units are much better.
Any input would be appreciated.

Asked By Bill Perkins | Feb 25 15

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