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!

5 Answers

Geothermal heat pump to preheat propane water heater water?

I have an older house that was built in the early 60s. The first floor has poured concrete foundation walls on the rear and sides of the house. One side and the back of the house is 5' into a soil... one side is about 1.5' into the soil and the front is at grade. When we bought the house it had a heat pump that ran the primary cooling and heating needs. It runs forced air through ducts in the attic and down to the first floor using ducting through some closets. This system is on its last leg.

Asked By user-6999468 | Jul 18 18
10 Answers

Do I need a whole home dehumidifier?

Hey GBA,

Here's a question that might be suited more for lennox guys. Unfortunately, asking high pressure sales reps from HVAC companies, well they just have no clue what I'm talking about.

So in my HVAC design, I am spec'ing an SLP98 Variable Gas furnace, XP14 AC and a Vanee 60H+ ERV, and the S30 Smart thermostat. I will do a 4 zone system.

I was thinking about what to do for humidity control.

Asked By Jamie B | Jul 1 17
2 Answers

Digital vs. VRF Scroll Compressors?

I'm looking at two different heat pumps, one using a digital scroll and the other a VRF (variable speed) scroll compressor.

The digital scroll compressor modulates output by separating the scrolls on a duty cycle, essentially a mechanical way of turning the compressor on/off as necessary while keeping the motor running. Modulation is from 100-10%.

The VRF scroll compressor modulates output by varying the speed of the compressor. Modulation is from 100-30%.

Asked By Lance Peters | Nov 29 17
12 Answers

HVAC - Smaller HVAC for better than code insulation?

First off, - New home, climate zone 6A - pretty good home - target <1.5ACH50.

My HVAC guy provided me with manual J calculations for sizing the HVAC system and I noticed he just used code insulation values and average house build quality to determine the loads. When I asked him to re-run the numbers for my actual insulation values he said he could do that but it won't make any difference to the hvac system he installs as it will make no difference to the equipment installed.

Asked By Steve Mackay | Jul 6 18
2 Answers

Mini split head placement

I want to put a 24,000 BTU mini split into a single story structure that measures about 36 X 24. It is divided into one long space and three bedrooms across the back. I know I won't get anything into the BRs without open doors but the simplest location is on one of the narrow end walls in the main area. My question is whether the unit will adequately condition the whole space or if the localized feedback from the one end will control temps and the far end won't get cool. Or is it small enough that with the air movement I don't need to worry?

Asked By DavidAtAshby | Jul 6 18
3 Answers

Trane XV18 heat pump: How low does it modulate?

Anybody know how low the Train XV18 heat pumps can modulate, in both cooling mode and heating mode?

I'm specifically interested in the 2-ton model.

Also, anybody know the max heating capacity at 17 F?

The info is very easy to find for Carrier variable speed heat pumps, but I can't find anything from Trane itself detailing the specs of Trane's variable speed heat pumps.


Asked By Aun Safe | Jul 1 18
14 Answers

Where should I drain condensate from a high-efficiency furnace?

I have a high-efficiency furnace, installed in 1995 and I now do not think the condensate drain was installed correctly. It has now corroded and is leaking inside my basement.

Asked By Bob Allison | Jul 3 18
7 Answers

Ducted vs. ductless minisplit and silence

I'm trying to get to the most silent A/C in a small 1200 sq ft house (old construction) and am zeroing in on a mini-split system (prob 1x 15k-18kBTU and 1x 9k). I have a 2007 vintage Mitsubishi MSZ09UN wall-mount in a studio and while it's quiet it's not very quiet, e.g., when sitting reading or working silently it gets to our nerves after a while. That unit is rated 22dBA on low. I'm looking for quieter...

Asked By Tvoneicken | Jul 3 18
5 Answers

Insulation on ducts within conditioned space, condensation?

Hi, I am in the planning phase of a remodel of a 2 story house in the San Francisco Bay Area, Zone 3c. The ducted multi-split system's duct work will be located within conditioned space, and I plan on a tight install mostly with rigid ducting except for the final flex duct runs to the registers. The issue is in the 1st floor where I am attempting to run most of the ducts within ceiling joist bays (2 x 8" joists, so 7-1/4" actual) so I don't lose head room. The joists also sit on a few beams that have to be crossed, so there we are also constrained by the same 2 x 8" joist bay height.

Asked By user-7071760 | Jun 30 18
7 Answers

How would you expand an existing electrical panel?

I have a townhouse with a mix of electric and gas appliances. I don't like combustion inside a home, so I plan to make some changes to eliminate the gas burners. (These units are all original to the home and nearing end-of-life.)

The townhouse has an 11-year-old 150 amp service with a couple of unused breaker slots. I know it won't be enough for one or two new HVAC units (heat pumps, mini splits, or possibly ducted minis), an electric water heater (probably a 75 gallon Rheem Marathon but maybe also a heat pump unit), an induction cooktop, and a Level 2 charging station.

Asked By Steve Knapp CZ 3A Georgia | Jul 1 18
Register for a free account and join the conversation

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