HVAC Systems Failing After Insulation
11 posts since Jul 2026, all from r/hvacadvice.
“My furnace and water heater are in a mechanical room that's something like 500 square feet with 8 foot ceilings (or at least 8 feet to the floor joists). That makes for 4000 cubic feet of combustion air. My water heater is a traditional gas tank, 40k BTU. My furnace is 80%…”
“I'm trying to add air to a shared duplex basement to prevent back draft from 2 natural draft water heaters. I will replace the water heaters eventually (they are 7 years old) which will solve the sporadic air quality issue but will still leave me with excessive negative…”
“We have a 3-ton Rheem A/C (11/22) installed Jan. 2023 - Volts 208/240 - Single-family home 3/2. It had a rolling sound at one point recently (exterior). My A/C guy said it was due to low voltage and suggested installing a Timer at the compressor so that when it detects low…”
Homeowners are experiencing combustion issues, AC malfunctions, and low voltage problems with their HVAC systems after insulation work or other modifications. Concerns range from furnace performance to mini-split condensation leaks and the need for system upgrades.
SOURCES (11)
“Hello all, House: ~2,150 sq ft in northern Illinois. Current furnace is 14 yo, 100k BTU, 2-stage. Trying to decide whether 80k is enough vs replacing with another 100k (including humidifiers.) EDIT: Current furnace: High stage: 100,000 BTU input → 97,000 BTU output Low stage:…”
“Homeowner in need of advice here. We bought our North Carolina new construction home back in late '23. It is a two-story home totaling 3200sqft. It has a forced air furnace in the attic with two dampers that control upstairs/downstairs zones. The model number is a Lennox ML17XC1-041-230A01. According to Lennox info it's a 3.5 ton unit. The west side of the upstairs is a sauna in the afternoon, and about 5 degrees colder than the rest of the house during cold months. With the house being”
“My furnace and water heater are in a mechanical room that's something like 500 square feet with 8 foot ceilings (or at least 8 feet to the floor joists). That makes for 4000 cubic feet of combustion air. My water heater is a traditional gas tank, 40k BTU. My furnace is 80% efficient, 88k BTU. When I run the numbers that works out to 6400 cubic feet of volume I technically need for combustion air. Obviously this is only an issue in the winter when the furnace runs. I suspect in the past that”
“I live in south Florida and my house is 2100 sf. My old system is a 14 year old Rheem that would run over 20 hours a day trying to keep up. My house has impact windows and blown in insulation in the attic. A two stage system would be around 10k and a single stage for around 7k. Any feedback will be appreciated. submitted by /u/calle14 [link] [comments]”
“My home is well insulated. I’ve insulated the attic to r60 and air sealed. I removed interior window trim and air sealed as well as caulk around outside of windows and cellular shades on all windows. All the doors have been resealed and all, including interior walls, switches and outlets have foam gaskets. I set thermostat to 77° and rh is usually around 45%. The ac doesn’t run from 10:00pm to 11:30 am the next day and humidity will climb to only 47-48% and temp drops to 75-76° on a hot 90° day”
“I'm trying to add air to a shared duplex basement to prevent back draft from 2 natural draft water heaters. I will replace the water heaters eventually (they are 7 years old) which will solve the sporadic air quality issue but will still leave me with excessive negative pressure. *My plan is to use a pressure sensor / controller to trigger a fan to bring air into the basement. I will likely filter and condition the air. Possibly adding basement returns to let the hvac systems condition the a”
“sorry for the formatting This all the stuff I’ve done any help would be appreciated. Having troubles getting the outside unit to fire up when it’s call for duty is received. System Information - Equipment Type: Lennox AC Outdoor Condenser / Indoor Furnace - Thermostat: Hardwired Google Nest Thermostat (Gen 3 Color Screen) - Current Status: Indoor blower fan runs perfectly when called. Outdoor unit remains completely silent (no fan, no compressor, no hum). High-voltage supply is intact, but the l”
“We have a 3-ton Rheem A/C (11/22) installed Jan. 2023 - Volts 208/240 - Single-family home 3/2. It had a rolling sound at one point recently (exterior). My A/C guy said it was due to low voltage and suggested installing a Timer at the compressor so that when it detects low voltage, it shuts off, thereby protecting the compressor. He said the low voltage could be coming from "in the house" or from the local electrical company. He assured me that many people are having the same issue and”
“We're building an addition on our house. Installed this 18k mini split about 6 months ago and its been fantastic. Noticed this water leak on the drywall this weekend and thought it was a clogged drain line but found it was the condensation filling the foam Insulation on the charge lines. I cant find anything online. Do I have the lines routed incorrectly? Ive removed the foam for now but would line to know what needs to be done to prevent this going forward? submitted by /u/RichS”
“We have a 1800sq ft 2-story home in the mid-Atlantic region. It gets bitter cold in winter at least 2x a year and we get at least 2 heat waves in the summer. I know this unit works great in the winter, how does it perform for air conditioning in the summer? submitted by /u/truecrime938284 [link] [comments]”
“My air handler is located in a closet. Closet is split into 2 parts horizontally. Bottom is the air intake with 2 filters, one in each corner. The decision between the air handler compartment and the bottom intake portion is made of 2 by 4s. These 2 by 4s have gaps between them. How do I seal these gaps? My thinking is to tape them from the bottom with that metal looking ac fire retardant tape. Is there a better solution? Or is my idea good/professional looking enough submitted by /u”