(Heating, Ventilating, and Air Conditioning) For questions about installing, repairing, and troubleshooting HVAC systems.

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35
votes
4answers
145k views

How can I add a “C” wire to my thermostat?

So, the spiffy new wi-fi thermostats want power on the C wire from thermostat, but the old thermostat doesn't have a C wire at it. What's the easiest way to add the C wire/24 volt to the thermostat ...
18
votes
1answer
10k views

Humidity Levels

What is a healthy and safe humidity level that I should try to keep my house at?
14
votes
3answers
7k views

Is running ethernet cable through an air return allowed under US code?

I'm looking to wire up the second floor of my house and the cold air return provides a convenient, straight run from the office to the utility room. Is it safe and within code to run ethernet cable in ...
14
votes
4answers
12k views

Why don't programmable thermostats automatically switch between “Cool” and “Heat”?

While I can set my house to be a particular temperature, I still have to manually switch it between "Heat" and "Cool" mode, and this seems to be true of every thermostat (programmable or not) that ...
13
votes
4answers
68k views

What are the pros and cons of a whole house humidifier?

In the winter, my house (~2500 sqft) becomes unbearably dry. Last winter, my wife and I used a tiny humidifier for the master bedroom to keep us from completely drying out, but since then I have been ...
12
votes
6answers
592 views

Is it worthwhile to have ductwork cleaned?

Was rearranging some ductwork in my basement, and noticed that the stuff I took down was pretty filthy inside (especially the return air ducts). Is it worthwhile to have ductwork cleaned out? What ...
12
votes
3answers
386 views

Would providing shade for my air conditioner's condensor improve its efficiency?

Our house has two A/C systems; one for the bedroom level, one for the remainder of the house. The compressor/consdensor units are outside the south side of the house, and in direct sun all day, now ...
11
votes
3answers
5k views

Ethernet cable instead of Thermostat wire?

I need to pull new wire from my furnace to my thermostat and was wondering if there would be any problems in using an Ethernet cable instead of standard thermostat wiring. The reason being is I have ...
11
votes
5answers
7k views

How can I calculate how large an airconditioner my house needs?

I know there are a lot of possible factors that go into determining the size of the air-conditioning system a house needs. Is there a standard way of calculating what is needed, or do A/C companies ...
11
votes
2answers
9k views

Why is my Nest thermostat not working with A/C?

I installed Nest thermostat a few weeks ago, replacing an old Lux programmable thermostat (there was nothing wrong with it). I connected 4 wires (R,W,Y and G) to the Nest. But as soon as I'd ...
10
votes
9answers
12k views

Do thermostat-controlled, auto-adjust HVAC vents exist?

The residential forced-air HVAC systems I have seen are controlled by a single thermostat in one room. One has to manually adjust the vents in order to adjust the temperature in other rooms. Is ...
10
votes
2answers
12k views

What does a Summer/Winter switch on furnace air ducts do?

On some of our furnace ducts, there is a switch/valve for Summer/Winter or S/W. What does changing this switch/lever accomplish? Can bad things happen if I forget to switch it? Bonus question: ...
10
votes
3answers
87k views

What's the most common cause of A/C refrigerant lines freezing?

I noticed my house wasn't getting under 75°F this weekend when I had the thermostat set for 70°F. Since I'd done a lot of drywall sanding inside recently, my first idea was to replace the filthy air ...
9
votes
5answers
2k views

Why won't HVAC supply stores sell directly to the public?

I am quite shocked that every store in my very large metropolitan area that sells HVAC supplies requires purchasers to have HVAC contractors license. Which makes it very difficult for a very ...
9
votes
4answers
14k views

Does lowering the blower speed of a forced-air furnace lower its efficiency?

My gas furnace has two options for the blower speed: MED, and MED-HI. It had been set on the higher speed, but that was too harsh, so I lowered it to the slower speed. Does that have any impact on the ...
8
votes
1answer
3k views

How do you trigger the hvac with wiring only?

I have a HVAC that has the usually wiring C R G W Y Pinouts What wires do I need to connect to turn on Heating? What wired do I need to connect to turn on the A/C? Is there a risk of damaging any ...
8
votes
1answer
302 views

Should I relocate the HVAC unit in my attic?

I have had a couple of estimates to replace our HVAC system and one contractor says he would relocate the system to a more central location in the attic. One says there is no need to relocate. There ...
8
votes
4answers
729 views

What type of regular maintenance should I be doing on my central air conditioning unit?

I have not done any maintenance on my central air conditioning system since I bought my house five years ago. Everything seems to be running fine but is there some sort of maintenance I should be ...
7
votes
5answers
11k views

How much cooling can I expect from a central air conditioner?

Yesterday's high was 106.0F, low of 79.2F, full sun all day. AC set at 78F, indoor temperature reached about 85F. Today's high was 105.4F, low of 81.1F, full sun all day, now about 102 at 7pm. AC ...
7
votes
3answers
1k views

How can I reclaim heat from an enclosed furnace room?

Our home has two furnaces (oil fired hot air) and an electric water heater in an enclosed room (approx 6'6" x 9'). Three walls of the room divide it from the remainder of a finished basement, the ...
7
votes
4answers
5k views

Can I modify the vent from my high efficiency furnace to prevent possible damage to the exterior of my home?

is my high efficiency furnace vent installed properly? I'm based in Toronto, Canada. In some recent cold winter weather, the exhaust is causing a lot of ice buildup on the surrounding brick. To my ...
7
votes
2answers
3k views

Why are almost all of my house's HVAC floor registers placed near exterior windows?

My current house is a single story built over a crawlspace and all the HVAC registers are in the floor. In all of the larger rooms, at least one (and usually more) register was placed near an exterior ...
7
votes
6answers
9k views

Where should my furnace filter go in a Lennox G40UHX series furnace?

I have a Lennox G40UH(X) series furnace, which is installed in our attic (We have a single-story house on a slab). Because the furnace is installed in the attic, it is "laying down" on its side, and ...
7
votes
1answer
568 views

Why did an HVAC installer add this PVC pipe?

We recently had a VERY old central heating furnace replaced and I noticed that the HVAC installer added the following PVC pipe shortly before the inspector arrived: The metal vents were already ...
7
votes
3answers
2k views

Are new “low noise” whole house fans actually quieter?

I've dealt with a number of older whole house fans (10 years and older) and the one thing they all had in common was a ton of noise. Are the new "low noise" fans actually that much quieter than the ...
7
votes
2answers
889 views

Is there any legitimate reason to have a direct vent between utility room and attic?

I've been doing some sealing and insulating in my attic, and discovered a purpose built vent directly from the utility room into the attic space. See most of these photos The house is in a ...
7
votes
1answer
34k views

Why is my air conditioner tripping the circuit breaker?

Our air conditioner recently stopped blowing out cold air. When I went to check on it, I noticed that the outside unit wasn't coming on. We had had problems with ants in the contacter in the past, ...
7
votes
1answer
1k views

AC issues / Insulation of vaulted ceiling

Issue: If it's hot outside, ~90F, house temperature can't get below 79F. Background: 6 year old house, vaulted ceiling with 1 ceiling fan in family room where thermostat is (also 3 large windows, ...
6
votes
7answers
2k views

Should I apply car wax to the outside of my air conditioning unit?

Through different conversations with family members and friends, I have been told that it is good to apply a coat of car wax to the outside of the air conditioning unit frame. I assume that this is to ...
6
votes
3answers
668 views

Why is my power flickering across multiple circuits?

I woke up this morning and went downstairs to find that none of the lights would come on (lights were working fine upstairs). My first instinct was thinking that a breaker had tripped, so I went to ...
6
votes
4answers
1k views

Why aren't Geothermal heat pumps more common?

Air conditioning and heating are major energy consumers in American buildings - commercial, residential, and industrial. I have been curious for a while as to why it isn't more common to use the ...
6
votes
3answers
3k views

How can I determine why my A/C runs all day?

I have a Bryant AC/Furnace unit. My house is 10 years old. A heat wave hit this weekend & temps got up to 95°F outside. I had my thermostat set to 75°, and it ran all day. The ...
6
votes
4answers
1k views

Heating/cooling system recommendations for this small house?

I will soon build my first house and I need to choose what type of heating/cooling system I'll have installed. I know very little about this and I'm seeking recommendations, ideas, suggestions, etc. ...
6
votes
3answers
1k views

How do outdoor mist-cooling A\C units fare in real-world usage?

I live in Phoenix where summer outdoor temperatures regularly exceed 110°F and humidity around 15% or lower is not uncommon. In this environment a mist system can easily pull the temperature down ...
6
votes
1answer
713 views

Orange flame on all appliances

I have an orange flame in all my gas appliances (gas furnace, gas water heater, and gas stove) and cannot seem to determine the cause. Background So far, I have had the gas company come out. I had ...
6
votes
2answers
24k views

What are the pros and cons of two AC systems vs a dual zone system?

I have a Cape Cod with 1000 ft2 on the first floor and an apartment in the attic. In a few years I may get rid of the apartment and build up a second story + attic. Both the first floor and the ...
5
votes
4answers
259 views

How can I keep a bedroom warmer in summer?

The master bedroom in my parent's house tends to be the coolest room in the house, and my father complains it's too cold. The A/C register in the ceiling does have a flow adjustment lever, but it's ...
5
votes
6answers
14k views

How often should I run a bleach and water solution through condensate lines?

How often do you need to run a bleach and water solution through the condensate drain lines (of a heat pump) to keep the bacteria away? What are the recommended parts (e.g. 1 part bleach, 10 part ...
5
votes
2answers
773 views

When insulating with closed-cell Spray Foam, what ERV and HVAC resizing considerations should I bear in mind?

I am building a 2800 sqft, two-story brick home in Austin, TX. I have heard many good things about the benefits of insulating with closed-cell Spray Polyurethane Foam (ccSPF)1, and have requested ...
5
votes
2answers
1k views

How to best keep floor vent by shower dry/mold free?

We just moved into a rental home. It turned out after living there for a few weeks that we discovered the vents were innudated with mold. They were so bad the landlord had to replace all the vents in ...
5
votes
3answers
87 views

How to find areas where heat/coolness are lost?

I live in a 2-story rental townhome (basically an apartment with 2 stories). Our central air/heat system isn't really the best at keeping the upstairs and downstairs the same temperature whether in ...
5
votes
2answers
5k views

How do I install a wood stove as an auxiliary heat source?

I have a house with a forced air electric furnace. We've also got a wood-burning stove adjacent to the furnace. I didn't have it installed, and I want to understand if it's been done properly, and ...
5
votes
2answers
938 views

Is it safe to install a sconce light box inside a return air space?

In my finished basement, the space between one section of studs is being used as a return air duct for my furnace and central air. Here is a picture, looking up from the vent at the floor level: ...
5
votes
2answers
5k views

HVAC vents - does wall or ceiling mount matter?

I'm going to add some crown moulding to some bedrooms. I've got HVAC vents mounted near the top of the wall and the moulding will cover part of the vent. I want to move the vents out of the way. I ...
5
votes
2answers
5k views

Is it OK to have heating registers and returns near the ceiling?

I've got a question about a new house - a friend of my mother's is buying a new place and when she did a walkthrough (before the drywall was up), she noticed that all the heating registers and returns ...
5
votes
2answers
3k views

Should I be concerned about fridge/freezer airflow?

We just recently had the following counter/cabinet system put into our basement family room. After everything was done, I started to get concerned about airflow. The enclosure was built in such a ...
5
votes
3answers
131 views

What concerns should I have installing a HVAC unit and ducts in a home that's never had it?

We're looking at a house in southern Alabama that has no central heating and air. I would like to put one in. The house was built in 1950. What should I be considering about the installation?
5
votes
2answers
1k views

Can an HRV replace the air exhausted by a range hood?

I'm in the process of buying a 1950s ranch house. It doesn't have the greatest insulation, so I'm planning to do some improvements over the first few years to tighten things up. I'll certainly do the ...
5
votes
1answer
135 views

Does lack of zone control delay hurt heat pump?

I had a new HVAC single heat-pump system installed with dual zone controls: 2 thermostats and 2 dampers for separate zones. The system works, but the zone control board does not have any time ...
5
votes
1answer
977 views

Do I need to increase my HVAC trunk line size?

I'm thinking of finishing my basement. I currently have a main trunk coming off my furnace that measures 20" wide by 6" tall. I'm trying to future proof my home in the event my current furnace can't ...