A winter morning story that explains the “why”
It’s 6 a.m., twelve degrees outside, and the house feels chilly. The heat pump hums, but warm air takes a minute. Then it hits a defrost cycle and blows cooler air. You tug on a hoodie and wonder if the system is struggling. It’s not failing. It needs help for the coldest hours. That help is the backup electric heat strip. Think of it as the dependable spare tire that keeps you moving when the road gets rough.
The Furnace Outlet, we help you choose the right strip size, not the biggest one. We share honest math, not hype. Our licensed techs talk you through options by phone or chat, and we ship fast, often free at wholesale prices. Let’s break down sizing, costs, wiring, and smart controls so your heat pump stays comfortable, efficient, and ready for deep-freeze mornings.
What a backup heat strip actually does
A heat pump moves heat from outdoors to indoors. As the outdoor temperature drops, its heating capacity falls. During very cold snaps or defrost cycles, supply air can feel cooler. A backup heat strip fills that gap. It’s a simple electric element inside the air handler that adds heat on demand.
The strip does not replace your heat pump; it supports it. You can stage it to step in only when needed. That protects comfort while keeping bills in check. If you’re pairing a new strip with a new system,
Browse our air handlers and R-32 heat pump systems.
The cold-climate sizing sweet spot
In cold regions, a common best practice is simple. Size the heat pump close to your cooling load, then size the heat strip to handle the remaining heating need at your design temperature. Many pros target 80%–100% of the design heat load for strips. That coverage keeps rooms comfortable during defrost and rare equipment hiccups. Example: a 3-ton heat pump equals ~36,000 BTU/hr. Some homes pair it with an 8–10 kW strip to cover most or all of the design load. Others choose a smaller 5 kW strip when the goal is just freeze protection. To tighten estimates, get a Manual J load calculation.
If you don’t have one, ask our licensed techs, or use our Design Center to start right and avoid guesswork. When you’re ready to shop, our accessories section has breakers, kits, and controls.
More strip kW isn’t always better. Aim for “enough,” not “max.”
Comfort guard during defrost and outages
Defrost is normal. The outdoor unit briefly reverses and can blow cooler air inside. A right-sized backup heat strip masks that dip and keeps supply air warm. It also helps during a brief outage or compressor fault, buying time until you can troubleshoot. You can stage strips so only part of the capacity turns on first. That softens electrical demand and trims costs. If defrost comfort is your main concern, a moderate kW strip may be perfect. If your design temperature is very low and your house is older, lean higher. Unsure which you are? Snap a few photos and get a no-pressure recommendation through our Quote by Photo tool. We’ll suggest the simplest fix first and never push a full replacement unless it makes clear sense.
The cost reality: strips vs. compressor
Electric strips turn electricity straight into heat. That’s simple but not efficient. Your heat pump’s compressor usually delivers the same heat for about one-third the cost. That’s why we try to let the compressor do the heavy lifting. Use controls that turn strips on only when outdoor temps dip below set points or during defrost. You’ll feel steady comfort without the shock on your bill. If your panel is tight on capacity, a modest kW strip plus smarter control can be the sweet spot. Ready to compare system options?
How many kW do I need? A quick table
Use this table for ballpark planning. Confirm with a load calc and your electrician.
|
Heat Strip (kW) |
Approx. BTU/hr |
Typical Breaker |
Notes |
|
3 kW |
~10,200 |
20–25 A |
Light backup, freeze protection |
|
5 kW |
~17,100 |
30–35 A |
Common with efficient homes |
|
8 kW |
~27,400 |
45–60 A |
Solid defrost and cold snaps |
|
10 kW |
~34,100 |
60–70 A |
Close to full 3-ton coverage |
|
15 kW |
~51,200 |
80–90 A |
Large homes or very low design temps |
BTU/hr ≈ kW × 3,412
Actual breaker/wire size depends on heater listing and local code.
Electrical panel and wiring checks
Bigger strips draw more current. That can push panel limits and add installation cost. Before choosing 10–15 kW, confirm available amperage, wire size, and breaker spaces. Many air handlers accept staged kits, which split the load across two circuits. That helps when panel capacity is tight. An electrician can verify conductor sizes and breaker types. If the panel is small, go with a right-sized strip and smarter controls instead of oversizing. Our licensed HVAC techs can help you balance comfort and wiring realities on chat or phone. If you decide to upgrade equipment later.
Controls that save: staging, lockouts, and sensors
Controls decide when strips energize. Good thermostats and air handlers allow staging (part of the strip first, then more if needed). They also support auxiliary heat lockout above a chosen outdoor temperature, so the compressor handles mild cold alone. Add an outdoor sensor to make this precise. Some installers set a lower lockout to protect comfort during shoulder seasons. Others prioritize energy savings and push the lockout higher. Either way, tune it after a week of real use. Watch your supply air temperature and room feel. Need help choosing a thermostat or kit? Chat with us through the Help Center.
DIY path: from load calc to cart
Here’s a simple step-by-step plan.
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Get a load calc. Use Manual J software or ask us via the Design Center.
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Pick your heat pump system. See our R-32 heat pump systems.
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Choose an air handler that accepts staged strips. Browse air handlers.
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Select the strip kW to cover the remaining load.
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Add controls with aux lockout.
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Verify panel capacity and breakers.
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Order what you need. We keep prices wholesale and shipping fast, often free.
Example sizing: a typical 3-ton home
Let’s say your Manual J shows 38,000 BTU/hr at 5°F design temperature. Your cold-climate 3-ton heat pump delivers 24,000 BTU/hr at 5°F. The gap is 14,000 BTU/hr. A 5 kW strip yields ~17,100 BTU/hr, which covers the gap with a little cushion. Set staging so only part of the strip energizes first. Add an outdoor sensor and set an aux lockout near 25–30°F. The compressor will carry mild days, and the strip fills the deep-cold gap. If your panel is tight, a 3–5 kW kit may still keep you safe and comfortable. For product choices with quick shipping, check our R-32 packaged heat pumps and matching accessories.
Budget-friendly paths that still work
We respect budgets. Sometimes the smart move is a smaller strip now and a control tweak, not a panel upgrade. A 3–5 kW strip can guard against freezing and smooth defrost. If you later improve insulation or windows, your heating gap shrinks. You can revisit kW then. We’ll never push a replacement you don’t need.
Need payment flexibility? Our financing options help spread costs.
Your next step (and how we help)
Still deciding between 5 kW and 8 kW? Send us your square footage, insulation notes, and zip code. Use our Design Center or Quick Quote by Photo. We’ll give clear, honest advice, and often suggest low-cost tweaks before big changes. When you’re ready, shop directly with The Furnace Outlet for wholesale pricing and fast, free shipping. We stand behind our gear with real humans at Contact Us.
