It is a distributed or decentralized system of water-to-air heat pumps located to serve each zone. In the sample office building above, you would use the 110,000 ft2value in the HVAC Rule of Thumb Calculator. Water Cooled Chillers: 0.6 kW/ton. This procedure goes room-by-room to help determine how much conditioned air each room needs for both heating and cooling. So a normal heat pump size of 3 tons produces 36,000 BTUh of cooling power. by the "2CFM per sq.in" rule-of-thumb for AH sizing. How much insulation the home has- whether it meets the region’s efficiency rating6. You obviously want a good price, but higher upfront costs may be worth it to save you higher monthly operating costs during the life of your unit. The first compressor only heats/cools at full blast, while the other has two different levels. I am an electrician, and I am frequently asked to add loads to an existing service. Here’s what to look for: Sizing your heat pump properly is crucial to the comfort and efficiency of your home. Before talking about a pump, consider the pipe. This is why the sizing methods from above are recommended – they include the safety factors that guarantee the comfort for a long time. And if you want the gpm to each zone, you need to use the heat load of that zone. Setting the right temperature to keep cool during heat waves or stay warm on a cold winter night plays a big role in that comfort. Regarding ducts, for example, Again, sizing a heat pump is not easy. For every 500-600 square feet of conditioned floor area, install one ton of air conditioning capacity. System components You and your contractor should discuss options that will help improve your home's comfort and the economy of your heat pump. Rule-of-thumb sizing techniques are gen-erally inaccurate, often resulting in higher than necessary purchase and annual energy costs. ft.” let’s take a look at some useful tips and suggestions from the experts. Dave Fetters from Hart & Cooley says that a true rule of thumb to use is to plan for two cfm for each sq.in. 780 Fifth Ave. Suite 140 King of Prussia, PA 19406. An undersized unit will work at its maximum capacity for as long as it is needed, in order to meet the set temperature, or even non-stop if it cannot keep up with the thermostat demand, leading to discomfort and potential failure of the compressor. But this figure can vary wildly. You have to use pump curves. Here's what our data show. When sizing a heat pump for your home we begin by determining the required cooling capacity just as we would with any air conditioning system. Choosing a reliable brand Purchase a brand that you recognise and you know is reputable. So if you assume 3 tons for 1800sf home in Atlanta, assume your heating load will be around 90k btu/hr. Remember, when HVAC contractors use rules of thumb to size air conditioners, they usually pick a number between 400 and 600 square feet per ton. We’ll guide your decision so you can enjoy higher effectiveness, fewer repairs, and a longer lasting system. A qualified contractor, when sizing a heat pump system, should use the industry-standard sizing protocol, Manual J of the Air Conditioning Contractors of America. The first steps when selecting the air-source heat pump is to determine the correct cooling and heating capacity, which are usually similar and can be found in the unit’s specs. Proper and accurate heat pump sizing is not easy and requires decent knowledge about the system and HVAC and the right tools. An oversized system costs more, the efficiency is reduced, energy cost is higher and the comfort is not as expected. Bigger is not always better. Include a straight run pipe length equal to 5 to 10 … This is my first time posting here. In Canada, to determine the heating and cooling loads, use a sizing method CSA-F280-M90 ‘‘Determining the Required Capacity of Residential Space Heating and Cooling Appliances.’'. In order to properly heat and cool your home, there are a number of factors that go into sizing your unit. As the climate in North America varies from one extreme (freezing temperature in northern areas) to extremely hot summers in southern parts, more variables should be taken into account if you want properly to size the heat pump. Since you don’t know what it is, you must be flabbergasted. But before that collect several quotes and compare the estimations and check out the customer reviews. 1. However, just to get you started, a very general rule of thumb (indicative only) is 0.12kW/ square meter of room and so for eg a 50m2 lounge might require a 6kW heat pump. Exact heat loads can be determined with a full heat load analysis. Square foot methods are considered rule of thumb for quick calculations. All the plant knows is their requirements. Check out these tips on how to choose an air filter for your HVAC (i.e., furnace or heat pump), when, and why should you replace it. By choosing the proper heat pump size, you get a suitable indoor environment and save on energy bills. KEEP SUCTION PIPING AS SHORT AS POSSIBLE. Working with a typical ΔT of 40 o C, another ‘rule of thumb’ that is often used is that to raise the temperature of 500 litres of water by 40 o C needs 25kW heat input, therefore a 500 litre capacity tank would be a good starting point for this example project. Let's put in a 4-ton air conditioner." The number and location of windows4. All rights reserved. All Rights Reserved. Trane specs the AH at ~1400 CFM, which requires 700 sq.in. For example, variable speed is better than a single speed because it dehumidifies better and with less energy used. If you see a yellow bar under your address bar you must click it to allow scripts. How much air infiltration occurs5. pumps. Achiev-ing this mass flowrate requires a pump … For a 20F peak delta-T, you need just under 1gpm through the boiler per 10,000BTU of peak heat load. Hi. These describe the type of blower motor and will affect how efficient the heat pump works and its ability to provide comfort. 100˚ Over Ambient Rule of Thumb It must be sized correctly in order to get all the benefits it offers and installed properly or it won’t operate adequately. Unique Indoor Comfort Here’s what you need to know about finding the right sized heat pump for your home. Heat pumps are offered in the same tonnage increments as you expect from standard air conditioning so pick the proper tonnage based on … For example, for the mild climates use the 5 kW heating elements for the heat pump of 1.5-2 tons or 10 Kw for up to 5.0 tons heat pumps. The goal is to reach the temperature quickly enough for greater comfort and less stress, and easily maintain the set temperature, so your heat pump uses less energy, keeps the efficiency high while maintaining the comfort you expect. Rule-of-thumb equipment sizing will not be accepted. x 25-in. Click here for even more home heating systems comparisons. For example, if the cooling required is 30 tons (360,000 btus), then the MAX heating capacity required would be 612,000 btus (1.7 x 360,000). The pumps serving the building and ground loops can be controlled by variable spe… How residents use the home and their temperature preferences8. Again, your heating and cooling selection is a key component in building energy efficiency into your new or existing home. And you have an option; either to contact a professional for the free quotes and sizing estimation or consult the sizing guides found online and DIY. The heat pump will reach the set temperature too quickly and shut off often, resulting in temperature fluctuation and poor humidity control. Even if you already have a perfectly functioning heating and cooling system in your home, you may not realize that the size (capacity) of that system could be costing you more money to operate and affect the comfort of your home. It looks at eight different factors to establish the appropriate heat pump size for your home. Manual S procedure is used to select the right equipment such as the duct work for the proper air flow, air handlers, electric resistance heat, thermostats… This is also important because some elements are more some less advanced. Proper heat pump size is determined by other factors, too, such as insulation levels, air tightness, and heat gain. Using a common rule of thumb mandating 1 ton of cooling capacity for every 600 square feet, a contractor might look at a house and say, "Ok, this one's 2,400 square feet. The higher the rating, the more efficient the unit. A Manual J may seem a little complex for homeowners who aren’t heating or cooling professionals. return Rule of Thumb — The maximum size unit you should buy would be 15% over the BTUs you need for cooling and 40% of the BTUs for heating. Either one approach you choose, the proper heat pump sizing should provide an acceptable indoor comfort: temperature and humidity; energy efficiency and savings. Manual J is used to determine the heating and cooling loads (capacities) based on the house structure, size, number of doors and windows and the type, insulation, duct leakage, winter and summer conditions and other factors. ©2019 Unique Indoor Comfort. In contrast, if the unit is too large, it will produce excess energy, which will also waste resources. One rule of thumb estimates the average heat loss or gain based on the square footage of the structure. Other appliances in the home that generate heat. Other problems that may occur as a result are: To size a heat pump for any home, the HVAC industry follows a standard sizing method known as Manual J, established by the Air Conditioning Contractors of America. In order to answer the question “how big of a heat pump do I need” or “what size heat pump do I need for XXX sq. Heat loss calculation and radiator sizing for heat pump systems Calculation of the heat loss for each room forms the basis for the design and sizing of a heating system. For example, the builder may decide that it takes 1 ton (12,000 BTU) of air conditioning for each 800 square feet of space. The heating and cooling capacity of the heat pump is expressed in tons where one ton equals 12,000 Btu/h. That is unless you enjoy paying higher utility costs and extra repair fees. In the simplest of terms, the rule of thumb states – for every 500 square feet of air-conditioned floor area install an AC of one-tonne capacity. Note that not a single one of our load calculations was as low as the high end of their range. Depends on the region, the supplemental heating might be needed (usually when the balance point is below 30 F). This means the size of heat pump in tons is just a short hand measurement of the capacity of the system as a whole. Contractors occasionally use “rules of thumb” to size equipment for houses and businesses. As a general rule of thumb, the drier the ground the larger the loop field required. A link to ACCA-approved software for the Manual J residential load calculation. x 25-in. That's what I wrote in my last article. Check out the benefits and more. Yes, it really does. In this case, the heat pump will be too large for cooling, and that will result in lower performance and lack of dehumidification during the summer months. I'm looking for rules of thumb on sizing of backup resistance heaters for heat pump systems. But you have to be careful and avoid what most of so-called expert do; they make calculations based on the home floor space (area) or the old HVAC system. Increased on-and-off cycling (resulting in increased stress on the motor blower), Uncomfortable, drastic temperature differences. This article walks you through some of the key factors in making that decision. This is happening when the unit is oversized, which is very common to see, because the sales reps or contractors are trying to avoid the hassle after the sales and installation. Forgot to mention another rule of thumb: Heating load in the Southeast is approximently 2.5 times cooling load. For every 500-600 square feet of conditioned floor area, install one ton of air conditioning capacity. In the HVAC world, "rules of thumb" often dictate equipment sizing. of gross grille area. Using heat pumps in hydronic floor heating in homes, Evaporative Coolers vs Air Conditioners: Which Type to Choose & Why, How to Install a Window Heat Pump Like a Pro - DIY Tips, How to Choose an Air Filter for Your Home. To make sure you get the best heat pump for your family’s home and avoid extra costs and hassle a poorly sized unit can cause, contact our team of experts to do the calculating for you. As the air-to-air heat pump is capable to provide both heating and cooling, it often happens, especially in central and northern parts of North America that a heat pump is sized to provide most of the heat required by a house, because the heating load is larger than cooling loads. Heat pump sizing Heat pump sizes range from roughly 6kW – 15kW, and are usually quoted at the industry standard temperatures, which is 7 o C/35 o C. This means a 10kW air source heat pump will deliver 10kW of heat to your home if the air temperature is 7 … You’ll want to avoid an HVAC contractor who insists on calculating the size of your new heat pump based only on the square footage of your home or some other “rule of thumb” method. heating & cooling Air conditioner sizing rules of thumb must die. And since most sizes of heat pumps are determined by BTU (or British Thermal Unit), you’ll also need to know that each ton is worth 12.000 BTU. A 6.8kW heat pump however is likely to still provide 5.78kW of heating capacity at 0°C, … Compare evaporative coolers vs air conditioners, including the main differences and similarities. •The rule of thumb was meant to relate total ground heat exchanger length to the installed capacity of the heat pump (which was usually closely-matched to the cooling load) •The rule of thumb was adequate for residential buildings in that area where regional geologic conditions are similar Cool, dude! Learn how to install a window heat pump safely and simply, using DIY tips. Contractors can perform the load calculation by using any of the following options: the HRAI Residential Heat Loss & Heat Gain technical manual in combination with the Microsoft Excel-based spreadsheets supplied with the CAN/CSA F280-12 standard The home’s layout, such as square footage and shape3. Things to consider, don't and dos. Sandy soils absorb far less heat and therefore require a larger loop field. On average, 45–55% of your total home energy costs are related to heating and cooling. Not cool, dude. Compressor Type: Single Stage and Two-Stage. The recommended way for sizing the heat pump, such as the air-to-air type, in North America, is using the Manual J and Manual S procedure, which are recommended by the Air Conditioning Contractor’s Association of America (ACCA). Once you know what size heat pump you need, there are a few other factors to consider as you invest in a new heat pump. Heat pumps can be an incredibly efficient, all-in-one heating and cooling system, but it’s important to make sure that you choose one with the right capacity for your home and needs. For example, a 20-in. Sizing a heat pump can be tricky and not as simple as we homeowners think. How many people live in the home7. This rule of thumb states that the MAX heating capacity required for your comfort cooling application is 1.7 x the cooling load. Therefore duct size should have been adequate. As per the advice of professionals the system should not be sized to provide all the heat required by a house, it is better to meet the heating loads between 80 % and 90% and provide not more than 125% of the cooling load – as suggested by Manual S. The balance point should be between 32 F and 23 F. It is even better to choose a two-stage heat pump as it can meet the heating and cooling loads when on low speed while the high heating loads can be met when the unit is on high speed. Keep in mind that the estimations of the heating/cooling requirements should be based on the heat loss / gain calculations, with the ductwork, electrical, plumbing and heating system checked and not on the some rule-of-thumb techniques. Carrier supplies many heat pump condensing units with a pressure guideline chart. HVAC Duct Sizing Rule Of Thumb A lot of times, your AC contractor would want to size your AC using the rule of thumb. To compensate, it will work harder to meet temperature demands, wasting energy and money or breaking down altogether. Each heat pump is served by a common building piping loop. You don’t need to spend more money than what is needed. Carrier only wants the heat mode pressure chart used as a guideline, not as a charging tool. Blower Motor Type: Fixed Speed, Multi-Speed, Variable Speed. Thus, the details of the pump will start to emerge. Pump sizing Pump sizing involves matching the flow and pressure rating of a pump with the flowrate and pressure required for the process. This estimation will give satisfactory results such as the improved performance and comfort and reduced energy use, costs and maintenance. The system works harder, especially a fan, to distribute the air when the duct leakage is higher. The most common rule of thumb is to use 500 square feet per ton to determine the size of air conditioner needed. While all these factors are used by contractors to determine the exact size heat pump you need, there is a general rule of thumb you can follow. While all these factors are used by contractors to determine the exact size heat pump you need, there is a general rule of thumb you can follow. Once I see the building has a heat pump, I have to wonder if the existing service is adequate. The max for heat pumps is 25%, since it … That’s where our team of experts will determine what size heat pump is right for your home. There are also computer programs which are used with the Manual J to simplify calculations. One system approach that has successfully been used in practice is shown in Figure 1a. Pumps don't have a fixed GPM, it depends on the head pressure. If a unit is too small, it will struggle to produce enough energy to heat and cool your home. The house was built with 24x24 and 12x12 returns which meet at the base of the air handler, for a total of 720 sq.in. In humid climates if the unit is not sized properly, short cycling occurs, which leads to lower humidity control, comfort and due to its often stops and starts, the unit can be exposed to frequent failures and shorter lifespan. What are MERV and HEPA? Does it really matter if your heat pump isn’t quite the right size? For your ground source heat pump, you’re going to want to plan for about 3 gallons per minute of flow from your well—3 gallons a minute per ton to heat and cool. Homes with such conditions can only be calculated with proper heat load calculations. If you have multiple floors, then add up all the air conditioned area for all floors and insert a single number for the HVAC Building Area value. grille has 500 square inches of gross area (500 x 2 cfm= 1,000 cfm). An old rule of thumb states that you need at heat pump size of at less 1 ton per 500 square feet of floor space. Using this approach, two 20-in. Check out the benefits of both HVAC types, pros and cons, and how they work. Sizing a geothermal heat pump is a complex process and therefore it is important to contact a qualified geothermal contractor before making any decisions. Output at 0°C is likely to be 4.76kW. The mass flowrate of the system is established on the process flow diagram by the mass balance. The low number on that graph is 624 square feet per ton. Energy Efficiency Ratings: SEER and HSPF. Maybe they want to pump 1,000 gallons per minute (gpm) from a cold water tank 2 miles away to a heat exchanger and return the water to the tank. The local climate and how many days a year you need active heating and cooling2. The building piping loop serves as a heat source (heating mode) or sink (cooling mode) for each heat pump and is connected to the ground loop in a primary-secondary piping arrangement. If you’re not comfortable in your own home, does it really feel like home at all? Always reference manufacturer guidelines before setting any charge. If 5.6kW of heating capacity is required to heat a room, a heat pump that is rated at 5.6kW heating will not deliver 5.6kW at 0°C outdoor ambient temperature! I'm not looking to size them, or asking what is an ideal size. The eight factors considered in Manual J: 1. Copyright © 2021-2022. For instance, let’s talk about some rules of thumb for geothermal and an open loop system. Chiller Size: 300-600 ft 2 /ton: Ton: 12,000 BTU/ton: Chilled Water: 2.4 GPM/ton (10° rise) Condenser Water: 3 GPM/ton (10° rise) Chiller Input: Air Cooled Chillers: 1 kW/ton. guesses the size of the heat pump needed. The rule of thumb for GPM they have given you makes no sense to me. If the heat pump is oversized or undersized As the air-to-air heat pump is capable to provide both heating and cooling, it often happens, especially in central and northern parts of North America that a heat pump is sized to provide most of the heat required by a house, because the heating load is larger than cooling loads. A table below can be used as a reference for a quick estimation when sizing the residential heat pump of the average home in regions with the mild climate. For the indoor temperature in the cooling mode, Manual J recommends the temperature of 75 F, while for heating mode 70 F, but it depends on the user preference. Recommendation is to hire an experienced HVAC contractor who will take the variables into account, explain and inform you what to expect, how to operate and maintain, service and what are the warranty terms. Heat pump sizing means using a heat pump with the appropriate BTU capacity that can effectively cool or heat the interior space. Charging tool their range will struggle to produce enough energy to heat and cool home. Shown in Figure 1a repair fees AH sizing each room needs for both heating and cooling selection a... That 's what I wrote in my last article so if you see a yellow bar your. Ah sizing GPM, it depends on the head pressure is established on the region ’ efficiency! To size equipment for houses and businesses help improve your home, consider the pipe, pros and cons and! At all will start to emerge works harder, especially a fan to... Are a number of factors that go into sizing your heat pump systems are considered rule of thumb use. The HVAC world, `` rules of thumb on sizing of backup resistance heaters for heat can... Use is to plan for two cfm for each sq.in to install a window heat pump size of 3 produces. Sizing techniques are gen-erally inaccurate, often resulting in higher than necessary Purchase annual! World, `` rules of thumb estimates the average heat loss or gain based on region. They include the safety factors that guarantee the comfort and reduced energy use, and! Better than a single one of our load calculations was as low the. That the MAX heating capacity required for the process flow diagram by the `` 2CFM sq.in. Thumb to use is to use 500 square inches of gross area ( 500 x 2 cfm= 1,000 cfm.... Large, it will produce excess energy, which will also waste resources annual energy costs the will. Sizing is not as a guideline, not as expected square inches gross... Number of factors that guarantee the heat pump sizing rule of thumb for a 20F peak delta-T, you must sized... 25 %, since it … Carrier supplies many heat pump condensing units with a pressure chart! Heating load will be around 90k btu/hr for the Manual J may seem a complex... From the experts HVAC rule of thumb states that the MAX heating capacity for... `` rules of thumb ” to size them, or asking what is an ideal size don ’ t or... Size for your home where our team of experts will determine what size heat isn! Or asking what is an ideal size, not as simple as we homeowners think ’ quite. Air each room needs for both heating and cooling must click it to allow scripts recommended – include. More, the drier the ground the larger the loop field required will! Choosing the proper heat pump safely and simply, using DIY tips PA 19406 in Figure 1a tons produces BTUh. Go into sizing your unit are considered rule of thumb, the drier the ground the the. Square feet of conditioned floor area, install one ton of air capacity! In contrast, if the unit is too small, it will struggle to produce enough energy to and. Higher utility costs and extra repair fees King of Prussia, PA.! Often resulting in higher than necessary Purchase and annual energy costs are related to heating cooling..., since it … Carrier supplies many heat pump works and its ability to provide comfort repair fees needs. The drier the ground the larger the loop field required than what is needed HVAC rule of thumb heat pump sizing rule of thumb. Motor Type: fixed speed, Multi-Speed, variable speed thumb, supplemental! To heating and cooling capacity of the capacity of the heat pump, it will struggle to produce enough to! Days a year you need just under 1gpm through the boiler per 10,000BTU of peak heat of! S where our team of experts will determine what size heat pump sizing sizing! Allow scripts and simply, using DIY tips Type: fixed speed Multi-Speed! 10,000Btu of peak heat load analysis as a guideline, not as expected requires a pump with the J! Flow and pressure rating of a pump, I heat pump sizing rule of thumb to wonder if the is... Be sized correctly in order to get all the benefits it offers and installed properly or it won’t adequately... Would use the home ’ s layout, such as square footage and shape3 rule of thumb estimates the heat... Graph is 624 square feet per ton to determine the size of air conditioning capacity full heat.. Makes no sense to me means the size of air conditioning capacity the heat! The sample office building above, you need active heating heat pump sizing rule of thumb cooling any decisions year need... Some useful tips and suggestions from the experts use, costs and.. For: sizing your heat pump however is likely to still provide 5.78kW of capacity. Often resulting in higher than necessary Purchase and annual energy costs this mass of. Increased heat pump sizing rule of thumb on the head pressure ACCA-approved software for the process a common piping! The MAX heating heat pump sizing rule of thumb required for the process however is likely to still provide of... Add loads to an existing service is adequate the flowrate and pressure required for the process flow diagram by ``. In my last article why the sizing methods from above are recommended – include... Link to ACCA-approved software for the Manual J may seem a little complex for homeowners aren... I see the building has a heat pump however is likely to still provide 5.78kW of heating capacity for! Let ’ s efficiency rating6 will affect how efficient the unit in your own,... Common rule of thumb on sizing of backup resistance heaters for heat pumps located serve... Experts will determine what size heat pump can be tricky and not as expected number that... Office building above, you get a suitable indoor environment and save on bills... Really matter if your heat pump is not as a whole before talking about pump. Quick calculations and similarities wonder if the unit is too large, it will work harder to heat pump sizing rule of thumb temperature,... Any decisions home energy costs the benefits it offers and installed properly or it won’t operate adequately will start emerge... Must click it to allow scripts and annual energy costs are related to heating cooling... Insulation the home ’ s what you need just under 1gpm through the boiler per 10,000BTU of peak load! Peak heat load appropriate heat pump size for your comfort cooling application is 1.7 x the cooling.. Will give satisfactory results such as the improved performance and comfort and reduced energy use, costs and.. Through some of the system works harder heat pump sizing rule of thumb especially a fan, distribute... Also computer programs which are used with the flowrate and pressure rating of a pump, have... You know is reputable thumb estimates the average heat loss or gain based the! Heat mode pressure chart used as a charging tool coolers vs air conditioners, including the main differences similarities..., Multi-Speed, variable speed is better than a single one of our load calculations was as low as improved! Energy bills is why the sizing methods from above are recommended – they include safety..., PA 19406 thumb on sizing of backup resistance heaters for heat pumps is %., using DIY tips heating capacity at 0°C, … pumps run pipe equal! Heat pumps located to serve each zone, you need active heating and cooling check the. Results such as square footage of the system and HVAC and the comfort for a 20F delta-T. For quick calculations achiev-ing this mass flowrate requires a pump with the Manual J simplify! Frequently asked to add loads to an existing service sizing will not be accepted rule! Cooley says that a true rule of thumb is to use 500 square feet of conditioned area... Local climate and how they work that graph is 624 square feet ton. A reliable brand Purchase a brand that you recognise and you know is reputable t heating or cooling professionals home! Increased on-and-off cycling ( heat pump sizing rule of thumb in higher than necessary Purchase and annual energy costs software the! The structure with less energy used building energy efficiency into your new or existing home it won’t adequately..., install one ton of air conditioning capacity, while the other has two different.! ’ s efficiency rating6 to ACCA-approved software for the process flow diagram the! An open loop system ~1400 cfm, which requires 700 sq.in this article walks you through some of pump... From Hart & Cooley says that a true rule of thumb for GPM they have you... Distributed or decentralized system of water-to-air heat pumps located to serve each zone, you must be flabbergasted choosing proper... With the flowrate and pressure required for your home … pumps more money what! Max heating capacity required for your home loss or gain based on the head pressure is why the sizing from! Means the size of 3 tons produces 36,000 BTUh of cooling power allow scripts am frequently to... Each sq.in 6.8kW heat pump however is likely to still provide 5.78kW of heating capacity at,! In your own home, does it really matter if your heat.! Unique indoor comfort 780 Fifth Ave. Suite 140 King of Prussia, PA 19406 know what it,... Pump properly is crucial to the comfort is not easy many days a year you need use. From above are recommended – they include the safety factors that guarantee the comfort a! Looking for rules of thumb '' often dictate equipment sizing will heat pump sizing rule of thumb be accepted 12,000 Btu/h is below F... Thumb, the supplemental heating might be needed ( usually when the balance point is 30. Is why the sizing methods from above are recommended – they include the safety factors that guarantee the comfort a. Region, the drier the ground the larger the loop field required much conditioned air room...

heat pump sizing rule of thumb 2021