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Questions tagged [hvac]

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

91
votes
7answers
497k 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 ...
27
votes
6answers
284k 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 ...
25
votes
6answers
15k views

How to improve HVAC system to make upstairs rooms more comfortable?

My home was built in 1985 in the US with conventional HVAC design of that time. Wooden frame house. It has central air conditioning (ducted) and we upgraded to a natural gas furnace recently. We ...
23
votes
1answer
33k views

Humidity Levels

What is a healthy and safe humidity level that I should try to keep my house at?
21
votes
7answers
24k 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 ...
19
votes
3answers
23k 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 ...
19
votes
1answer
149k 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 wires do I need to connect to turn on the A/C? Is there a risk of damaging any ...
19
votes
4answers
373k 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 ...
18
votes
2answers
6k views

Half my house losing power, HVAC the key factor

For the past couple of weeks I have been losing power occasionally to half my house. My central AC goes out, half my kitchen, living room and my kids' rooms. There are no tripped breakers though. I ...
18
votes
10answers
29k 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 ...
16
votes
4answers
65k 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 I'...
15
votes
3answers
4k views

Condensor went, HVAC guy is blaming electrician, is this possible?

My brand new HVAC unit, the condensor died. The unit has a sticker that says the following: Minimum Circuit Ampacity 32 amps Max Fuse / Breaker 50 The electrician ran a 8 gauge wire with a 40 ...
15
votes
6answers
707 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 ...
15
votes
3answers
7k 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 ...
14
votes
6answers
4k views

Is Electric Central Heating worth it if using Solar Panels?

I understand that electric heating is less efficient and comparatively more expensive than gas heating (propane or natural gas), but considering I live in Texas (a lot of sunlight) and I intend to ...
14
votes
2answers
50k views

Can I run a central air conditioner in the winter?

What happens if you run a central air conditioner when it's below freezing outside? Is this expected to work? I know, it sounds crazy, but that's because you don't live in an overheated New York ...
12
votes
2answers
3k views

How can I transition a square duct to round of the same outer size?

In remodeling my bathroom I had to convert a 6"x6" square duct underneath the floor joists in the basement to flex so I can get around my new toiler drain. I cannot for the life of me find a 6"x6" ...
12
votes
5answers
23k 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 ...
12
votes
5answers
72k 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 ...
11
votes
6answers
44k views

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

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 ...
11
votes
2answers
4k views

What is this device I found in my HVAC duct?

I was looking through my HVAC ducts with a camera and found this device attached to the side of a floor joist. It is about 2-3 feet from the air return vent. What is it?
11
votes
7answers
56k 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 ...
11
votes
1answer
113k 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, ...
10
votes
11answers
22k views

How can I increase the heating efficiency of a forced air system?

What are some DIY ways to increase the efficiency of a forced air heating system? Please answer in Community wiki fashion: 1 tip per answer. As @Jay Bazuzi pointed out, tips can also include ways to ...
10
votes
2answers
75k 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
2answers
2k views

What's the best tool for cutting holes into duct work?

I've cut a few supply and cold air returns into my main branches and it's been a PITA. Need to cut another 6" hole for a return, it's just standard rectangle ductwork, probably 14" wide x 10" high.
10
votes
8answers
38k 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 ...
10
votes
2answers
91k views

How do I identify the C terminal on my HVAC?

How do I identify the C terminal on an HVAC, furnace, or boiler? If the terminals don't have a screw labeled C what should I look for on the wiring diagram? What steps should I take if a wiring ...
10
votes
4answers
6k 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 ...
9
votes
5answers
103k 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 ...
9
votes
2answers
31k views

What could be causing an 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 ...
9
votes
1answer
566 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 ...
9
votes
6answers
1k 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 ...
8
votes
11answers
58k views

How much less power does a three-phase air conditioning unit use than a one phase unit?

I'm planning to install a 5 ton central AC. I'm deciding between a condensing unit that runs on 220V and a costlier unit that runs on 207Y three-phase. My understanding is that three-phase motors use ...
8
votes
6answers
101k 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 ...
8
votes
6answers
33k 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 ...
8
votes
5answers
71k views

What kind of wall switch is needed for a natural gas fireplace to ignite consistently?

When we moved in, our natural gas fireplace worked well: Flick the switch & it would ignite. Years later, it started acting erratically: Sometimes, the switch worked, other times, no luck. We'd ...
8
votes
9answers
19k 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 ...
8
votes
3answers
100k 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 ...
8
votes
1answer
113 views

What kind of professional to call for help with structure-borne noise issues from HVAC

We are in a multi-story, multi-unit building that uses packaged through-the-wall HVAC systems in each unit. These units often go under the name of "Magic-Pak" or "Comfort Pack" depending on the ...
7
votes
2answers
3k views

Should I bypass a thermal cut-off switch on my oil furnace?

My thermal cut-off switch for my oil furnace blew and my neighbor replaced it until a tech could come out and check it when I had my cleaning. The switch blew again and the furnace tech bypassed the ...
7
votes
5answers
3k 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 ...
7
votes
2answers
29k 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
2answers
691 views

Who do I hire to design my home HVAC system?

Preface I need to buy a new HVAC system for my 1930s home. I currently have forced air duct system. My gas furnace was installed in 1985 and is rusting out, and I'm not sure about the air conditioner....
7
votes
3answers
5k 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
2answers
2k 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 part ...
7
votes
2answers
1k 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 ...
7
votes
4answers
82k views

How can I improve second floor HVAC performance?

I have a forced air heating and air conditioning system that performs poorly on the second floor: It is way too warm in the summer and a little too cold in the winter. I live in a 1920s masonry row ...
7
votes
1answer
4k 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, ...
7
votes
2answers
6k 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 ...