If you’ve ever stood over a floor register with your hand out like you’re checking a campfire, you know the moment: the system kicks on… and the air feels wrong. Maybe it’s lukewarm. Maybe it’s straight-up chilly. Then—finally—it turns warm and you think, “Okay, we’re back.” And then it flips again and you’re right back to muttering at the thermostat.
That exact frustration is why today’s post exists—because I keep hearing variations of the same questions:
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furnace blows cold air then hot
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furnace blows hot then cold
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heater blows cold air then hot
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why does my furnace blow hot air then cold
And since a lot of homeowners pairing a heat pump with electric backup, or running all-electric heat, end up with a Goodman MBVK-based setup, we’re going to talk about the Goodman MBVK “electric furnace” configuration: what it is, why those temperature swings happen, when it’s normal, and when it’s a red flag.
I’ll keep it real, I’ll keep it practical, and I’ll keep it focused on what helps you stop playing “hot-or-not” with your vents.
First: what the Goodman MBVK actually is (and why people call it an “electric furnace”)
The Goodman MBVK series is best described as a modular blower / air handler cabinet built to do indoor-air-handler duties—moving air across an evaporator coil for cooling—and, when paired with an electric heat kit, it can operate as electric heat for the home. In other words: with the heater installed, it can function like what most folks mean when they say “electric furnace.” Goodman positions MBVK as an air handler platform (with ComfortBridge capability on certain models), and the installation literature spells out the “blower cabinet + electric heater = electric furnace” idea very plainly. You can see that on Goodman’s MBVK product page and in MBVK installation documentation. (Goodman MBVK Series overview) (MBVK install manual PDF)
Why that matters: an MBVK system’s “weird” air temperature behavior often isn’t a failure. It’s the natural result of how air handlers, heat strips, heat pumps, blower delays, and thermostats actually behave in the real world.
So before you assume something’s broken, let’s decode the most common hot/cold patterns.
The #1 misunderstanding: “My furnace is blowing cold air” versus “My system is moving air before it’s heated”
Here’s the truth nobody tells you on the day you move in:
A forced-air system doesn’t wait for a perfect-toasty moment to start moving air unless it’s set up that way.
Depending on controls and settings, the blower can:
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start immediately with a call for heat,
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start after a short delay (to let heat build up),
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or keep running after heating stops (to squeeze out leftover heat).
Those delays are normal and can be adjustable depending on the control board, heater kit, thermostat behavior, and whether you’re using communicating controls.
So if you’re searching furnace blows cold air then hot, what you might actually be experiencing is “blower starts, heat ramps up a few seconds later.” That’s not the same as “the furnace can’t make heat.”
Now, if you’re searching furnace blows hot then cold, that’s the reverse: heat stops, but the blower keeps running a bit and you feel the leftover air temperature drop.
Both can be normal—or both can point to an airflow/control problem. The difference is pattern and severity.
Let’s break the patterns down.
Pattern A: “furnace blows cold air then hot” (and the air handler takes a minute to ‘wake up’)
1) Blower delay + electric heat staging (normal-ish)
Electric heat kits often energize in stages. You might have 5 kW, 10 kW, 15 kW, 20 kW—sometimes staged so the system doesn’t slam the electrical load all at once.
What you feel at the vents can look like this:
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Blower starts (air feels room-temp or cool).
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First heat stage warms up (air becomes warm).
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Additional heat stage adds more heat (air becomes hotter).
That “cool then hot” is especially noticeable if:
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ducts run through a cold attic/crawl,
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the system has a high airflow setting,
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or the thermostat starts the fan early.
2) Heat pump first, strips second (also normal)
If your MBVK is paired with a heat pump, your system may try to heat using the heat pump first because it’s usually cheaper to run (depending on your climate and rates). If the thermostat decides the heat pump isn’t keeping up, it brings on auxiliary electric heat.
Translation: early airflow might feel cooler, then the strips kick in and it gets hotter.
This is a very common source of heater blows cold air then hot complaints—because heat pumps deliver air that’s warm, but not always “furnace hot.” Your body expects a blast of 120°F+ air; the heat pump might be giving you something that feels mild.
3) Duct temperature “purge” (very common)
If the system has been off awhile, the ductwork is basically a long tube of whatever temperature the house/attic/crawlspace is. The first chunk of air you feel is that “stored” duct air getting pushed out. Then the heated air arrives.
If your ducts run through unconditioned space, this effect is amplified. DOE’s guidance on heating efficiency and duct performance is a good reminder that the distribution system matters almost as much as the equipment. (DOE overview on furnaces and heating efficiency)
What to look for: If it’s cool for 10–30 seconds and then warms up consistently, that’s often normal. If it’s cool for several minutes, we’re moving into “something’s off” territory.
Pattern B: “furnace blows hot then cold” (it was warm… then it wasn’t)
When homeowners say furnace blows hot then cold, they usually mean one of these:
1) Fan “off-delay” is doing its job (normal)
Many systems keep the blower running after the heat shuts off to:
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use the residual heat in the heater/coil,
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reduce short cycling,
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even out temperatures.
At first the air is warm, then as the remaining heat is used up, the air cools. That can feel like the system is “messing with you,” but it’s often just extracting leftover heat.
2) Thermostat fan set to ON (very common)
If your thermostat fan is set to ON, the blower runs continuously—even when there’s no heat call. That means you’ll often feel warm air during heat operation and cooler air between cycles.
This is one of the most overlooked answers to why does my furnace blow hot air then cold because it feels like a heating problem, but it’s actually a fan setting problem.
If you want steadier “only-when-heating” airflow, switch the fan setting to AUTO (unless you have a specific air quality/comfort reason to circulate constantly). Here’s a straightforward breakdown of what ON vs AUTO means in real life. (Thermostat fan ON vs AUTO explanation)
3) Heat strips are cutting out on a limit (not normal)
Electric heat kits include safety limits. If airflow is restricted (dirty filter, closed registers, undersized ducts, blower speed too low), the heater can overheat, trip a limit, and shut off the heat while the blower keeps running.
That creates the classic complaint:
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starts hot,
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then suddenly goes cool,
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then maybe returns hot again later.
That’s not a “quirk.” That’s a warning.
If the hot-to-cold swing is dramatic and repeats, you want to check airflow issues first.
Pattern C: “heater blows cold air then hot” specifically with heat pumps (defrost and changeover moments)
If you have a heat pump, there’s one moment every homeowner should know about: defrost.
During cold, humid conditions, the outdoor coil can frost up. The system periodically reverses operation to melt that frost. During defrost, the indoor side may temporarily feel cooler unless auxiliary electric heat is used to temper it.
This is one of the reasons people swear their system is “broken” when it might be acting normally. You’ll feel temperature weirdness during those transition periods—especially if the thermostat settings prioritize efficiency over comfort.
If your MBVK is the indoor air handler in a heat-pump system, those defrost/auxiliary transitions are a prime suspect behind both “cold then hot” and “hot then cold” moments.
Okay, Jake—how do I tell “normal behavior” from “fix it now”?
Here’s my quick reality-check list. If any of these are true, treat it as a troubleshooting situation, not a personality trait of the system:
Red flags that suggest a real problem
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The air goes cold for minutes at a time during an active heat call.
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The system alternates hot/cold repeatedly in one long call for heat.
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You notice burning smell beyond the normal “first heat of the season” dust burn-off.
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Breakers trip or lights dim dramatically when heat engages.
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The thermostat shows AUX heat constantly and bills are climbing fast.
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The system is loud, surging, or “hunting” (speeding up and down erratically).
If you’re mostly feeling a brief transition at start/stop of a cycle, that’s often within normal operation. If you’re experiencing sustained cold air during a heat call, we hunt the cause.
The most common causes (and what to do) for hot/cold swings on an MBVK electric heat setup
1) Dirty filter or airflow restriction (start here every time)
Restricted airflow is the silent troublemaker behind:
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heat strip limits tripping,
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uneven temperatures,
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noisy operation,
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and “hot then cold” complaints.
What to do:
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Replace the filter (don’t just “look at it”—replace it).
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Make sure returns aren’t blocked by furniture.
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Make sure supply registers aren’t closed all over the house.
Air handlers like the MBVK are designed around specific airflow targets. When airflow is wrong, everything else downstream gets weird.
2) Blower speed / airflow configuration mismatch
MBVK units can be configured for different airflow requirements depending on your system (cooling tonnage, heating setup, duct static pressure). If the blower is set too high, the air can feel cooler even though the system is heating. If set too low, heat strips can overheat and shut off.
Symptoms:
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“It’s heating, but the air never feels that warm.”
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Or: “It starts hot, then goes cold like a switch flipped.”
Best move: This is where a technician earns their keep with static pressure measurement and airflow verification, rather than guessing.
3) Fan settings / thermostat programming
If you want to avoid the emotional rollercoaster of feeling “cold air” between heat cycles, confirm:
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Fan is set to AUTO (unless you intentionally want circulation).
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Smart thermostat features aren’t set to run the fan after the cycle in a way you hate.
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Heat pump lockout / aux staging is appropriate for your climate.
That thermostat fan setting article I linked earlier is worth five minutes, because it solves a surprising number of complaints without touching the equipment.
4) Heat strip staging / sequencer behavior
Electric heat kits use controls (often sequencers or electronic staging) to energize heat safely. If a staging control is failing, you can get inconsistent heat output: hot, then less hot, then hot again.
Symptoms:
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Heat output seems “steppy” in a bad way.
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The home struggles to maintain temp.
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You feel sharp changes at vents during a steady call.
What to do: This is generally a service call. Electric heat components are not a DIY playground.
5) Heat pump defrost + aux heat interaction
If you have a heat pump matched with an MBVK, a lot of “cold then hot” drama is simply the system switching modes and using aux heat strategically.
What to check:
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Does it happen mostly on colder, damp mornings?
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Does it correspond with the outdoor unit sounding different?
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Does it resolve on its own?
If yes, that’s consistent with defrost/aux operation.
6) Duct losses and attic/crawlspace effects
If your ducts run through unconditioned space, the first blast of air may be heavily influenced by that space. Also, leaky ducts can make a system feel inconsistent—because the air reaching you isn’t what left the unit.
DOE’s heating efficiency guidance is a good reminder that “equipment efficiency” and “delivered comfort” are not the same thing if the distribution system is compromised.
Where the MBVK shines (and why it’s popular in all-electric or heat-pump homes)
Let’s talk about why the MBVK platform gets picked so often.
Modular design, flexible install
MBVK blower cabinets are designed to pair with a coil for cooling and can be configured in multiple positions depending on your layout. If your mechanical space is tight or the install orientation matters, that flexibility is a practical win.
Variable-speed blower capability (comfort and control)
Many MBVK configurations are built around variable-speed ECM blower performance and communicating features depending on the specific model and controls. That can mean:
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smoother airflow ramps,
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better comfort,
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improved dehumidification behavior in cooling mode,
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and less “blast and stop” drama compared to older constant-speed setups.
Electric heat compatibility
With the right electric heat kit installed, the MBVK can deliver strong, straightforward electric heat—especially in areas where gas isn’t available or where heat pump + electric backup is the plan. The MBVK installation literature explicitly notes its use as an electric furnace when paired with an electric heater.
So… why does my furnace blow hot air then cold?
Let’s answer that keyword question head-on:
why does my furnace blow hot air then cold
Most often, it’s one of these:
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Normal fan off-delay: heat stops, fan runs a bit, air cools at the end.
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Thermostat fan ON: blower runs even without heat, so you feel room-temp air between cycles.
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Heat strips hitting a high-limit: heat shuts off for safety, fan keeps going (this is the one you don’t ignore).
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Heat pump defrost or mode change: system transitions cause short comfort swings.
The “right” answer depends on how long the cold air lasts, how often it repeats, and whether the thermostat is actively calling for heat during the cold period.
My practical, homeowner-friendly troubleshooting flow (no tools required)
If you want a simple flow that catches the majority of cases:
Step 1: Check the thermostat
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Is the system set to HEAT?
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Is the fan set to AUTO?
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If it’s a heat pump system, do you see AUX or EM HEAT? When?
Step 2: Change the filter
Even if it “looks okay.” Filters can be deceptive.
Step 3: Walk the house
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Make sure returns aren’t blocked.
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Make sure you didn’t close a bunch of supply registers trying to “push more air” to one room (that often backfires).
Step 4: Notice the timing
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Cold for 10–30 seconds at the start? Often normal.
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Cold for 2–5 minutes during an active heat call? Troubleshoot deeper.
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Hot then cold then hot repeatedly? Suspect airflow limits or staging/control issues.
Step 5: If it’s repeating, stop guessing and get it measured
At that point, you want:
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static pressure checked,
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airflow verified,
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heater kit staging verified,
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and heat pump defrost/aux settings verified (if applicable).
The bottom line: comfort is a system, not a box
The Goodman MBVK is a solid platform when it’s installed and configured correctly. But the experience you have at the vents—whether you’re Googling furnace blows cold air then hot or furnace blows hot then cold—is shaped by:
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thermostat behavior,
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blower timing and speed,
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electric heat staging,
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duct design and leakage,
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and whether you’re running a heat pump with auxiliary heat.
If you want to read up on MBVK positioning and specs straight from the source, start with the official product overview. And if you’re the “show me the manual” type (respect), the installation documentation is where the electric-heat-as-furnace setup is described.
If after the basic checks you’re still getting big swings—especially sustained cold air during a heat call—treat it like a solvable mechanical/configuration issue. Because it usually is.
And no, you don’t have to live with vents that can’t decide what season it is.
