Community: Mechanicals

Q & A Instructions

[Click map to enlarge]

The web site has a wealth of articles on a wide variety of construction topics. Before posting your question, you may want to check out the articles on this page: How To Do Everything. You just might discover an article there that provides the information you seek.

Please register for a free account or sign in to ask and answer green building questions.

If you want to post a question, the usual rules of courtesy apply:
1. Be nice.
2. If you can't be nice, be polite.
3. If you can't be nice or polite — well, please be brief.

To attach a photo or illustration: Under the box labeled “More explanation,” look for the words “File attachments.” Click that, and you should be able to attach a photo.

Thanks for joining the conversation!

15 Answers

Geothermal - Sizing Issues - 4 Ton or 5 Ton?

I live in Cincinnati, OH and I am zeroing in on purchasing a geothermal heat pump for my 5800 SF (conditioned) home. My home is all electric is currently heated by an 8 year old 4 ton air source heat pump with 15Kw electric backup. My issue is the two geothermal companies I have contacted to quote the job disagree on heating load of my home. Both companies did Manual J calculations, but are coming up with different numbers. One company has the heat load at 55k BTU -- says a 4 ton is the way to go. The other company has heat load at 68k BTU - says go with a 5 ton unit.

Asked By joel perrine | May 3 15
6 Answers

What's a good damper for a bath fan/range hood vent?

My bath fan vent is basically a big hole in the house to the exterior and sucks air out of the house in the high New Mexico winds, which today reached 30 mph. There's no damper or air check valve or anything like that installed up there, and I'd like to rectify it. What do people use for this situation? A standard butterfly damper? Something louvered? This thing?

Asked By Nathaniel G | Nov 23 14
3 Answers

Thermal break and insulation for gas fireplace flue pipe

We are building a tight and well insulated home in WY. It gets very cold here. We are paying special attention to creating a thermal break and insulating all ductwork to the exterior. They installed a "one pipe" gas fireplace and the metal flue pipe comes straight from the outside with no thermal break. I am told that it must have one inch of air around it so we are not able to insulate the pipe. I had suggested stove pipe insulation which is fire proof but contractor says code does not allow anything.

Asked By John Culbertson | May 4 15
5 Answers

Need help puzzling through the details of outfitting my house with a mini-split system

Right now my house has a 19 year old 125,000 BTU 80% efficiency gas furnace with ducts in the unconditioned attic, partially buried under insulation. I'd like some help determining if mini-split heat pumps will work as replacements, and in what configuration.

Asked By Nate G | May 2 15
10 Answers

Has anyone had experience with the Unico small duct system?

I was looking at the top finishers for the department of energy's "Race to Zero Student Design Competition" ( ) and found the winner used the Unico system. I recall actually being in a home in Chattanooga once 15+ yrs ago that I believe had one of these systems, but I really know nothing about them. With the problems associated with finding small enough systems for well insulated homes and cost effective systems...does anyone know if I should be looking at this as an alternative?

Asked By Andrew Bennett | Apr 29 15
10 Answers

Recirculating OTR range hoods & washer/dryer ventilation

I'm installing an electric range in a small house, and am considering a microwave with a built-in recirculating over the range hood (with filter). The house is very small (500 s.f.) and pretty tight, and California T-24 code requires continuous exhaust ventilation, which I plan to have in the bathroom (Panasonic WhisperGreen), but I'm afraid if I put an additional exhaust fan in, I'd have to provide ventilation in from outside. How effective are these OTR recirculating hoods?

Asked By Dan Burgoyne | Apr 28 15
3 Answers

Sizing an HRV unit

Hello, community,

I am renovating my 1903 2 1/2 story colonial house in southern connecticut, zone 5a. The house is listed as 2,100 sq ft (ground floor + 2nd floor), but I am also finishing and including the attic into the building envelope, giving an additional 1,050 sq. ft. for a total of 3,150 sq. ft. of conditioned space. I will be using closed cell spray foam insulation in all walls and roof. Heating is hydro air, and cooling is central air. System is split on 2 units, one for 1st floor and one for the 2nd floor and attic.

Asked By gary bruzzese | Apr 26 15
8 Answers

Water heater standby losses

Does anyone have a reference for the standby losses (in BTU/hr) for a "typical" gas-fired 40 gallon water heater?


Asked By Pete Engle | Apr 28 10
3 Answers

iQ drive vs mini-split?

My last house (2700sf)was made with SIPS and had a traditional 16 SEER heat pump. It worked fine and despite a convoluted layout only had minor airflow issues. Now I'm building a smaller house (2000 sf) with double stud walls and better windows so I expect the envelope to perform better than my last house with 4" SIPS (climate zone 4 - east TN...go vols and all that stuff). I have been thinking of going with minisplits because they are all the rage...but with the inverter's used in Nordyns iQ drive couldn't it be close to as efficient?

Asked By Andrew Bennett | Apr 20 15
21 Answers

Is it reasonable to use 3/8" PEX supply lines to all fixtures?

I am planning the plumbing system for my Net-Zero Energy home that is being built to Passive House standards. I will be using PEX tubing with a manifold system using home runs. I designed the house so that the bathrooms and laundry room are centrally located, making the supply runs pretty short. I want to minimize the amount of water and energy being used and low-flow fixtures provide plenty of water for my needs (2.2 gpm at sinks and 2.5 gpm for showers).

Asked By Gerald Blycker | Mar 11 14
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!