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

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44
votes
4answers
203k 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 ...
5
votes
2answers
21k 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 ...
2
votes
2answers
1k views

Is a little ice on the cooling coils ok?

This is our first summer in a new house which has central air. It was a bit hotter today than normal so the AC was running for a long time. After awhile we noticed the airflow stopped because the ...
1
vote
2answers
3k views

Can you terminate more than one common on the furnace C terminal?

TL;DR: Can you terminate more than one common on the furnace C terminal? Background: I've linked a diagram of how my non-programmable thermostat is currently hooked up. I want to replace it with a ...
12
votes
4answers
171k 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 ...
15
votes
10answers
19k 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
1answer
66k 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, ...
5
votes
2answers
2k 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 ...
4
votes
7answers
9k views

Would putting a sprinkler on my roof help cool my home?

Anyone ever put a sprinkler on your roof to help out your A/C on unusually hot days? Just wondering if it helps.
3
votes
1answer
5k views

Convert line voltage heating system to use low voltage thermostats

I currently have two line voltage ceiling radiant heating systems in my condo each with their own DPST thermostat. I'd like to use low voltage thermostats such as the nest. I found this ...
3
votes
4answers
527 views

Air conditioning on a shoestring budget

Without purchasing expensive air-con units, or solar panels - and the associated moutings and electrical paraphernalia, is it possible to create a temperature difference of 10-20 °C using materials ...
4
votes
3answers
9k views

What's causing the rumbling sound when my furnace kicks on?

I have a new, 3-year old, high-efficiency furnace in my home. Last year it started making a slight whining noise that was audible during the very first stage, before the blower motor started. No ...
3
votes
3answers
10k views

Why is my furnace blower noisy when it starts?

The blower of my furnace makes a loud noise every time it starts. I understand that a large fan and the movement of large amounts of air will produce some noise. What I am puzzled by is the noise that ...
3
votes
1answer
8k views

How should I wire this White-Rodgers fan and limit control? What about the thermostat?

I have a wood-burning stove, that is used as an auxiliary heat source in the house. There's a regular electric furnace, and adjacent to it is the stove. The warm air duct (out) from the stove ...
2
votes
1answer
2k views

Should I install a damper above my return air duct for better upstairs cooling?

I have a finished basement, ground floor, and upstairs. The ground floor and basement cool nicely with the AC. The upstairs doesn't cool very well. The returns are really just holes in the drywall- ...
18
votes
1answer
16k views

Humidity Levels

What is a healthy and safe humidity level that I should try to keep my house at?
11
votes
5answers
13k 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 ...
7
votes
2answers
41k 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 ...
16
votes
3answers
10k 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 ...
7
votes
2answers
1k 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
5answers
32k 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 ...
5
votes
2answers
2k 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
2answers
6k 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 ...
3
votes
3answers
21k views

Why is my furnace blowing cold air?

My HEIL 7000 natural gas furnace has stopped working what are the most likely causes, and how to verify faulty parts? Normal operation routine Thermostat sends "need heat" signal. Exhaust blower ...
1
vote
1answer
14k views

Should I add a return air vent in a refinished basement?

We are refinishing our basement, and are nearing competition. The walls are drywalled, and the ceiling is dropped. There will be about 500 sq ft of finished space, including a full bathroom, and ...
0
votes
1answer
540 views

Can I connect two wires to a single screw terminal in my HVAC system?

I am installing a new honeywell WiFi thermostat but the old battery operated thermostat had batteries and no "C" wire. I look at both the thermostat and the air handler and found an extra un-used blue ...
6
votes
9answers
30k views

How can I prevent my HVAC condensate drain line from freezing?

Last night, my heat (forced air) suddenly stopped. Today, a plumber figured out that my heater is 90% efficient, produces lots of condensate, and the drain line had frozen. We went outside and saw ...
6
votes
6answers
27k 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
2k 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
8k 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 ...
4
votes
2answers
1k views

Connection for C wire on Mastertrol Mark V zone control panel

I have spent hours searching the web for information on this 20+ year old zone control panel, which supports 3 zones of Heat and A/C. The thermostat I'm replacing (on Zone 3) connects to T4/T5/T6 as ...
4
votes
3answers
2k views

Is an interior laundry room without an HVAC vent a code violation?

Currently looking at a home which has a nice 2nd floor laundry. Vented dryer, nice rack for hanging clothes, etc. However, it's in the center of the home and does not contain an HVAC (central air) ...
3
votes
6answers
787 views

Air Conditioner Can't Keep up

We just rented a condo and our A/C cannot keep up so it will run almost constantly. It can't even keep the temperature constant, it will creep up into the 80s even while running. I measured the ...
3
votes
2answers
24k views

How can I prevent my house from smelling of smoke after having a fire in my fireplace?

We have a wood-burning fireplace in our family room. Fifteen feet from the fireplace is a large cold air return. When the fireplace is stoked, nice and cozy, everything is fantastic. When I shut it ...
3
votes
2answers
4k views

How do I install a jump duct?

Our master bedroom is considerably warmer than the living/dining/kitchen area of our house, and we've been setting the thermostat quite lower than we'd like in order for the bedroom to get cool enough ...
2
votes
2answers
378 views

How can I prevent my clothes dryer door from fogging up?

When I turn the air conditioning on in my house, the inside of the window in the clothes dryer door fogs up. Also, if clothes are left in the dryer, they become slightly damp again. How can I prevent ...
2
votes
1answer
5k views

Why won't my Heil 7000 natural gas furnace ignite?

I have a Heil 7000 gas furnace Model: NUGK100DH12 Serial: L933050100 When we turn it on at the thermostat, the exhaust blower will kick on. We checked to be sure the gas is reaching the unit and ...
2
votes
1answer
2k views

What could cause a replacement A/C condenser fan motor to only run for 3 minutes?

Just replaced a GE 5KCP39FG Condenser fan motor with an AC Smith FSE1026SF. HVAC Counter sales told me it was the right one and gave me a Partners Choice Capacitor 01-0085 to match. Old motor 3 ...
2
votes
2answers
10k views

AC Unit Blow Warm Air Indoor But Colder Air Outdoor

I have two AC Units. One for upstairs and one for downstairs. The upstairs one works just fine but not the downstairs. So, i did a test by turning both units on and went outside to compare the two ...
1
vote
1answer
519 views

New condenser fan motor burned out

AC technician replaced my condenser fan (through a home warranty service). The new fan worked for 5 min and stopped working after that. the fan motor was extremely hot (180F or more) The old fan motor ...
1
vote
2answers
22k views

Why do the evaporator and suction lines freeze when there is low refrigerant?

In an AC, why does a low refrigerant condition cause the evaporator, and/or suction line, to freeze up?
1
vote
2answers
6k views

How do I connect a dryer to a dryer vent?

I just moved my dryer (gas) a couple feet to a better location in the basement. It is actually now closer to the existing dryer vent to the outside of the house. The previous owner has it connected ...
1
vote
4answers
4k views

Are there efficient ways to provide combustion air to heating appliances?

In a previous question we established that there probably should be a vent between my utility room (which opens into the kitchen and living space in general) and the outdoors (in my case the attic, ...
0
votes
1answer
238 views

Duct static pressure vs ambient air pressure

I've read that air handlers are typically rated for 0.5 iwc. Doing a simple conversion, this comes out to about 125 Pa. Is this with reference to the ambient air pressure? So, if I had an absolute ...
0
votes
1answer
125 views

Fan coil wiring problem with new thermostat

I'm trying to upgrade to a new line voltage thermostat. The new thermostat has many more connections, including three fan speeds. My current system has a manual fan switch on the wall so all I need ...
0
votes
0answers
63 views

What could cause the heat side of our split pack heating/air unit to stop working?

Our heat side of our split pack unit (runs on propane) come on and will runs little bit but then won't come on again. We can turn it off for a while and then it will run again. What could be the ...
0
votes
0answers
237 views

possible HVAC Selector Wiring Solution?

I moved into my current home last winter. This house has an old zone controller MasterTrol Mark V model Mabs-V-3. UPDATE: just found that all wires connected to M? end nowhere. So I remove all the ...
0
votes
1answer
211 views

How to connect a DIY thermostat to the HVAC System

I am building a DIY thermostat similar to this blog. I want to connect it to the HVAC system of my home. How do I do that? I found this post which is very informative but doesn't completely answer my ...
0
votes
1answer
165 views

What is this fabric tape made out of?

Any ideas what is this fabric tape on my cool air return ductwork? High res close-up Some of it is separating or worse falling off of the duct work on the cool air return to my forced-air gas ...
0
votes
1answer
350 views

What type of dryer best handles long exhaust vents?

I have a very long exhaust line (about 5 meters) from the dryer and have issues with moisture staying in it when I do laundry. Since the old dryer broke down, I am now shopping around for a new dryer ...