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!

3 Answers

Will I have to be concerned with pipes freezing when I install a Mitsubishi Hyper heat system?

I have oil heat with forced hot water presently in my home in NH. The house is 5 years old and very well insulated. I want to add the Mitsubishi hyper heat to our house. It will have two indoor units one on each floor of our home. We are not putting a unit in the basement. It is primarily for cooling, but would like to use it to maintain the home at 55 degrees when we are not there. This is a vacation home so we are there mostly on weekends. My concern is that the oil burner will only be running to maintain hot water. We have a tankless unit off the boiler.

Asked By Rob Murray | Jul 14 16
4 Answers

Mitsubishi Heating Correction confusion

I am in the process of estimating the size of Mitsubishi FH series minisplits needed for a modular home in order to receive quotes from HVAC companies based on specific equipment requests and not their WAG assumptions. Will shortly be receiving a room by room Manual J heat loss calc.. The house will be located in zip code 12833 and so I am keenly interested in the minisplits ability to provide primary heating in an Upstate NY winter climate.

Asked By Doug Livingston | Jul 6 16
5 Answers

Replace bath exhaust fan details

20 year old builder poorly installed bath fan gave out so must be replaced. The fan is to the 2nd level master bath and the attic above is accessible unconditioned vented attic. I've read the GBA article on bath fans.

I've sized the fan properly. 400 cf room + 12' of duct with no elbows (I think; see below) + 30' to account for wall outlet = 60 cfm fan, per So I bought an 80 cfm fan. (Existing appears to be 40 cfm).

Asked By c l | Jul 4 16
22 Answers

Venting dryer inside house

I'm going to get absolutely roasted for asking this, but...

We're moving into a new house and will be replacing the old electric hot water heater with a new heat pump unit (probably a Stiebel Eltron) in the basement.

Separate but related, it appears the laundry room does not have a vent connection for the dryer (there is a second laundry area upstairs that the current owner appears to use as primary).

Asked By Matt Culik | Jul 6 16
8 Answers

Should I expel my ventilation system air onto my hybrid heat-pump water heater? Should I vent the WH into my crawl space?

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
2 Answers

Lightning surge protection for LED outdoor signage

A customer of mine wishes to replace his fluorescent tubes with LED tubes in his outdoor sign. I'm concerned about lighting strike surges. He has 12 two lamp 120v strips in his sign. Any recommendations? Thank you very much in advance for your reply.

Asked By Robert Turoff | Jul 7 16
8 Answers

Expensive electric combo boiler or cheaper electric boiler + water heater?

I've been siphoning off valuable information as a non-member for ages now, but no one seems to have spoken online about my current situation, so I'm happily forced to join the movement!
I'm contracting the build of my Southern Ontario as-close-to-Net-Zero-as-possible house, and have been left with two wildly disparate quotes from HVAC contractors to take care of my hot water needs. The system will be electric boiler-driven radiant floors throughout the 3200 sq. ft. home (wood stove backup), with accompanying HRV.

Asked By Jason Jazrawy | Jul 5 16
2 Answers

Ventilation calculation consternation

Are the following ventilation calculations correct?
Per (2013) ASHRAE 62.2 we need 3 cfm per 100 square feet plus 3.5 cfm per person.
So, a 3000 sf home with 5 occupants requires 127.5 cfm.
That's 7,650 cf per hour...
or 183,600 cf per day.
If the 3000 sf home has 8' ceilings, the total volume is 24,000 cf.
183,600 / 24,000 = 7.65
So, we're supposed to ventilate enough to change all the air 7.65 times per day?

Asked By Ben Rush | Jul 6 16
1 Answer

How do I find a good HVAC contractor?

I have issues with my ducting and what I can only assume is an unbalanced system. Some rooms are warm/cold, but others are fine. I would like to have a knowledgeable HVAC contractor help me out with my system, but I know that the general solution is to just throw "more power" at it. I'm looking for someone who truly understands the science of designing an efficient system, and this isn't something that can be determined from websites or reviews online. Does anyone have recommendations on how to find someone like that? BTW, I am in Minneapolis/St. Paul. Thanks.

Asked By Jay Johnson | Jul 3 16
20 Answers

Mini split advice

Climate Zone 5, Oakland County Michigan, building starting in July
2357 sq ft ranch, 2357 sq ft walkout basement.
2x6 walls dense pack cellulose, 3 inches exterior mineral wool
R60 ceiling insulation
Superior wall foundation for backfilled walls
R 7 Windows from Klearwall
Have access to natural gas but prefer to go electric if possible.

Thought I'd try and get your thoughts Dana and others on our Heating and Cooling plan. We just had a Manual J calculation done:

Total heating required including ventilation air: 37,561 Btuh

Asked By Brian W | Jun 22 16
Register for a free account and join the conversation

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