How to Choose the Right Size Heat Pump for Your Home

If you need a new heat pump for your home, one of the most important things is to make sure that you get a unit that is the proper size. This should be not only for your home, but also according to the local climate. Sizing a heat pump or any other HVAC unit is quite complicated and is something we recommend to be done by a professional to ensure accuracy.

To determine what size of heat pump a home needs, certified HVAC Comfort Specialists and Comfort Specialists generally use a special formula known as a Manual J load calculation. This calculation takes into account a variety of different factors. It is used to determine how many BTUs the heat pump needs to produce to effectively cool and heat the home. In this post, we’ll show you everything that goes into calculating what size heat pump your home needs.

Determine the Home’s Square Footage

The first step in sizing a heat pump is fairly simple. The total square footage of all of the conditioned living areas in the home provides a baseline for how large the heat pump needs to be. For homes with standard eight-foot ceilings, the Comfort Specialist will only need to calculate the square footage.

However, if you have high ceilings in some areas or throughout the entire home, the Comfort Specialist will typically need to calculate the cubic footage. High ceilings increase the total air volume in the home, which means your heat pump will need to be slightly larger or it won’t work effectively enough.

Calculate BTUs of Cooling/Heating Per Square Foot

The next step is to calculate the number of BTUs of cooling and heating you need per square foot, which is determined by where you live. In South Jersey, the general recommendation is that a heat pump needs to produce somewhere around 40 to 50 BTUs per square foot. If you have a 1,200-square-foot home with standard-height ceilings, you’d typically need between a 48,000- and 60,000-BTU heat pump.

All central heat pumps are measured in tons, and every one ton is equal to 12,000 BTUs. This means that a 1,200-square-foot home would usually need either a 4.5- or 5-ton heat pump. We usually wouldn’t recommend going with a 4-ton unit in this case. The reason is that it is always better to choose a unit that may be slightly larger than necessary rather than risk the unit being too small.

If your heat pump is too small, it will likely have issues keeping your home fully warm in the winter and cool in the summer. This means it will run for long periods and use lots more energy than a correctly sized unit would. The long run times are also why undersized heat pumps generally won’t last as long.

Similarly, a heat pump that is too large for your home will use more energy than necessary and is likely to have issues where it short cycles. Short cycling is when an HVAC unit never runs for more than around 10 minutes and continually cycles off and on in a short time.

Evaluate the Home

So far, we’ve estimated that a 1,200-square-foot home would likely need a 4.5- or 5-ton heat pump, but this is just an estimation. All homes are different, which means that what works for one may not be the best choice for another. This is why the Comfort Specialist will need to fully evaluate your home. This is because there are a number of other factors that could mean you need a smaller or larger heat pump.

Two of the most important things that the Comfort Specialist will need to evaluate are your home’s level of insulation and how well sealed its structure is. If you have a newer home that was built within the past 20 years or so, it is likely quite well insulated and properly sealed. In this case, your BTU-per-square-foot requirements will be at least a bit less than what we’d originally calculated.

The walls, ceilings and attic in many older homes tend to not be all that well insulated. The exterior structure or envelope in many older homes tends to be quite leaky, which means there are lots of places where air can escape and seep inside. This is especially pronounced in homes that still have old single-pane windows, as single-pane windows provide almost no insulating value.

These issues lead to a home experiencing lots of heat loss in the winter and much more heat gain in the summer. As such, homes that are poorly insulated and/or poorly sealed will likely have higher BTU requirements per square foot.

The number of exterior doors and the number, size and location of windows in the home also need to be taken into account. This is because windows and exterior doors are typically among the biggest contributors to summer heat gain and winter heat loss.

Another factor that the Comfort Specialist will take into account is whether the home receives lots of sunlight or is mostly shaded throughout the day. If your home receives lots of direct sunlight, it will experience more heat gain and get much hotter during the summer. This means you’ll need to make sure that your heat pump produces sufficient BTUs to combat this heat gain or it may not cool effectively enough.

The number of occupants also needs to be factored into the equation. The more people there are living in the home, the hotter it will get over the summer. This is why the Manual J formula calls for Comfort Specialists to add an additional 500 BTUs onto their cooling load for every occupant.

After evaluating your home and taking into account all of these various factors, the Comfort Specialist can then add up all of the numbers. This will allow the determination of exactly what size your heat pump needs to be.

Again, they will always err on the side of caution and recommend you go with a slightly larger unit if the numbers are too close. For instance, if they determine that the home needs 48,000 BTUs, they will almost always tell you to go with a 4.5-ton heat pump rather than a 4-ton unit. While the 4-ton unit may be sufficient and work effectively enough on most days, it could struggle on extremely hot or cold days. As such, the larger 4.5-ton unit would usually be the better option even though it will cost you slightly more.

South Jersey’s HVAC Experts

At Laury Heating Cooling & Plumbing, we’ve been proudly serving our South Jersey community for more than 75 years. Our certified Comfort Specialists have years of experience in all types of HVAC installation.

Therefore, we can help if you’re looking for a new heat pump, furnace, air conditioner or ductless mini-split. When you choose us, you can be certain that we’ll take the time to determine exactly what size your HVAC system needs to be. We’ll also explain all of your different options and help you find the best unit for your home and your budget.

We also offer professional HVAC maintenance and repairs as well as all types of residential plumbing services. Contact us today if you need a service appointment or to learn more about the range of heat pumps we offer.

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