Heat Pump and Gas Furnace Conversions for Houses with Electric Baseboard Heating By: Doug Baer Disclaimer: I am neither an engineer nor a licensed HVAC installer and thus provide no guarantees about the information in this article. Always obtain independent advice. I welcome comments from HVAC experts if I have misrepresented or misstated facts. I do have personal experience however. I initially installed a single, oldertechnology heat pump in the early 2000 s in a single room in my house, and upgraded nine years ago to a multiple heat pump ductless split system. Gas versus heat pump costs Here are the heating cost comparisons between gas furnace and heat pump systems. They are based on generating the same amount of heat (the amount of heat we would get if we ran a one kilowatt baseboard electrical heater for one hour). This would cost 13.26 cents at BC Hydro s current marginal electrical rate (I m assuming that, in winter, when you need heat you will be past the conservation threshold and paying 13.26 cents instead of the cheaper step 1 rate). Adding the 5% rate rider but not counting GST (which is common to both gas and electricity so it cancels out in making comparisons), we get 13.92 cents. [All figures are as of July, 2018.] To generate the same amount of heat using gas? I assume that the comparison is with a (more costly) high efficiency furnace and not a mid-efficiency furnace. The former tends to have efficiencies in the 90-98% range let s say 94% (mid-efficiency furnaces can be as low as 70% -- with some of the heat generated literally going up the chimney). And for heat pumps, I assume that it is an air source system. Using the formula that 1 gigajoule (GJ) = 277.8 khh, and using the current Fortis gas price for gas ($4.355 delivery charge;.758 storage and transport, 1.549 for the cost of gas, total = $6.662/GJ), we find that the equivalent to 1 kwh in heat generated by gas costs 2.398 cents. Factor in the efficiency ratio (1/.94) and we get 2.551 cents. What would have cost us 13.92 cents by baseboard heat is only 2.551 cents with gas. How does this compare to heat pumps? Using a single ducted heat pump system, our heat pump unit is connected into a ductwork system just like the comparison gas unit. I will use advertising brochure numbers the COP (co-efficient of performance) and the HSPF (heating seasonal performance factor). Usually, the COP is measured at a temperature that gives the best value (e.g., 10 degrees Celsius or 47-50F). As
gradients between the inside and outside temperatures get bigger (i.e., as it gets colder outside), it takes more electricity to generate a given unit of heat (for a much more detailed discussion of this issue, see below). This is an optimistic value unless the manufacturer has specified two or more different COP numbers for different temperatures to give you a better idea. The formula connecting HSPF and COP is COP = HSPF x.29307. Sometimes, these numbers won t match; usually, the HSPF multiplied by.29307 gives a number that is lower than the COP value cited. This is because HSPF provides a measure for the entire season. Once the COP is known, calculations are easy: 1 kwh of electricity gives the equivalent of 3 kwh in terms of heat if the COP is 3. So the cost of electricity with a heat pump is: HSPF COP Cost to generate equivalent to 1kW with baseboard 12 3.517.0359 (3.59 cents) 10 2.931.0475 (4.75 cents) 8 2.345.0594 (5.94 cents) 6 1.758.0792 (7.92 cents) Remember: the manufacturer specs are usually best case what the system achieves at an outside temperature around +10C. As temperatures fall, the efficiency drops (less so with the more expensive low temperature system), so the cost per unit of heat will go up. It would be helpful if manufacturers would supply tables or charts graphing heat generating capacity against ambient outside temperature. Another factor in the comparison is that one type of heat pump system the ductless type has less in the way of heat loss than either a heat pump or a gas furnace with a duct system (this would account for another 15%, perhaps more see below). In the past, systems with HSPF values of at least 8 have been eligible for energy grants. Some manufacturers today are advertising systems with claimed HSPF ratings of 12-14 or higher. So, heat pumps currently cost more to generate heat than gas furnaces. In the past decade, BC Hydro electricity prices have gone up much faster than gas prices. A decade ago, it cost the same or even less to generate heat using a heat pump in Victoria than to use a gas furnace. The price comparison assumes that a ductwork system is being used to transmit heat from a furnace or master heat pump unit to the rest of the house. There is heat loss through the duct system perhaps 10-15% in a well-constructed system, but as much as 20-40% where the ducts go through uninsulated crawl spaces (putting insulation around the ducts, a standard practice in these situations, helps somewhat), or where contractors have done a poor job and allowed for leakage. I have seen retrofitted duct systems in Broadmead that are not well-constructed. Assume a 15% heat loss in a ducted system (again, it can go much higher). This applies to central heat pump and central furnace systems, but does not apply to ductless
heat pump systems, where the heat loss is much less or, in some cases, effectively zero. Thus, a cost comparison between heat pumps and gas furnaces brings the two closer. (With a 15% heat loss, the gas cost for an equivalent of 1 kw of baseboard heat rises to 3.0 cents still cheaper than a heat pump, but not much.) How about air conditioning? Heat pumps act as air conditioners in the summer, with no need to reconfigure the system. For an energy grant, heat pump systems need to meet cooling standards as measured by the seasonal energy efficiency ratio. These numbers matter if you are seeking a grant. In Victoria, where air conditioning might be used a few hours a day for less than 30 days a year, I d care more about heating efficiency. Heat pumps will vary as outside temperatures fall An important consideration in determining the size of a heat pump system is that heat pumps generate less heat as the outside temperature goes down. (For example, my own systems, nominally 36,000 BTU each, generate 40,000 BTU at +10C but only 22,000 BTU at -10C and the 22,000 BTU at -10 uses the same amount of electricity as the 40,000 BTU at +10C). So, just when you need it the most, the heat pump generates less heat (and, for that matter, is less efficient, costing more per unit of heat). This is not a major issue above 0C, but if temperatures dip below -5C, some heat pump systems will have trouble keeping up unless they are oversized. Many systems including my own list -10C as the lowest operating temperature (in theory, they will stop operating, mostly due to freezing issues, below that temperature). Manufacturers have developed low temperature systems. These are more expensive and have much shallower efficiency gradients (for example, a 36,000 BTU system might still generate 32,000 BTU at -10C and not 22,000 BTU like my own). For temperatures in the -5 to -15C range, they will be much more efficient but as these temperatures rarely occur in Victoria. I tell prospective buyers don t bother unless the price difference is small. Some ducted heat pump systems have supplementary heat in the form of electrical resistance heaters. This tends only to be the case with central heat pump systems and not with ductless systems. I recommend against including any resistance electrical heating in the heat pump system: it s less expensive just to leave your existing baseboard heaters intact in case you need extra heat. (This has never happened to me my still-intact baseboard heaters are around in case anything happens to my heat pump system, but they have been gathering dust for years.) If your house cools down overnight, a system where resistance heaters are built in might automatically resort to the use of supplementary heat to bring the temperature up more quickly. Your heating costs can be driven considerably higher (it s as if, for part of
the heating, you never stopped using the baseboard heaters). This is because heat pump systems aren t as fast as gas furnaces. There s no harm in going over the needed heat demand in order to make sure you are covered for cold days, since the heat pumps can work at fractional capacity and not just 100% or off. I ve decided to get ductwork: What do I need to know? Get the HVAC contractor to commit to the exact configuration in writing, preferably with a diagram that is signed off by both parties. It is not uncommon for a contractor to promise the moon only to see something much different when the crew arrives. As in I m sorry, Sir, we just can t do that ). The actual is invariably a compromised version. A retrofit can work in a single-story home with a basement or crawl space. The new ductwork will be minimally disruptive. In a two-story house, it can get messy. A common strategy is to use closets to get ductwork up from one floor to the next (there goes some of your closet space!). Another is to put ducts up the corner of some rooms and frame them. The HVAC contractor can run into surprises though (an uninsulated space between floors, blocking joists, etc.). Ducts need to be run into each room to properly heat (or, in summer, cool) a home. A bigger issue is the placement of return air ducts. Return air ducts need to be large and straight to be effective. A cost-cutting contractor will be tempted to place one or two small air return ducts up to the second floor or worse skip return ducts altogether on that floor. This may not be so bad for heating, but is terrible for cooling. A second-floor room with a heat vent, but no air return, will not get heated as well as one with an air return. For effective air conditioning, you do not want both the supply and the air return vents in the floor. A standard practice is to put the air return up above shoulder height this is difficult in a retrofit. Since ductless heat pump system indoor units are usually installed high in the room, they do not usually have this problem. The HVAC contractor is going to make a mess. For example, you will find small holes in your walls that allow you to see into the next room. The HVAC contractor s job is to install a system. Budget for a carpenter or even a general contractor to fix the subsequent mess and assume you will need a drywaller and a painter also. There s one small consideration for those thinking of a ducted heat pump system: heat pumps generally produce air flows at a lower speed but with a greater need for volume, so the duct work should be slightly larger than the duct work that would be installed for a gas furnace system. Ductless Systems
Ductless systems are more efficient for either heating or cooling than equivalent ducted systems. Moreover, it is possible to maintain different room temperatures in different rooms, thus saving energy. A ductless heat pump system involves an outdoor unit, which heats or cools refrigerant, electrical wiring to power the indoor unit, and control wires and then a piping system of two refrigerant (supply and return) which pipes this refrigerant to one or more indoor units. See heat pump manufacturers websites. A condensate line to drain water is also needed when in air conditioning mode (usually to the outside of the house). These can be fished to the heat pump s indoor unit without tearing down walls as they require less space than air ducts. If a line is outside the house, it is usually insulated (fairly easy to do and with less heat loss than insulating an air duct). As with ducts, remediation is necessary, but the installation of ductless (or split ) systems does not involve as much destruction as ducted systems. (But do set aside extra funds to do fix-up work). Ductless systems tend to create an esthetic disruption as indoor units are only available in white. Some manufacturers have specialized slim units, and at least one has a unit that acts as a picture frame (so one can use art to hide the unit). These tend to crank out less heating and cooling, and are only, in my view, suitable for rooms or room areas where the demand for heating or cooling is low. Ductless fans make slightly more noise those of a heating duct. Review the specs of the to make sure the noise might not be too loud (especially in bedrooms). My own units have quiet mode sound ratings of 22 db(a); I find them to be virtually silent (on hi, they range from 39 to 44 db(a)). All heat pumps will go through defrost cycles. The heat pump will actually draw warm air from the house (and cold air will blow out, though usually with the heat pump fan on low ) for 5-10 minutes. Ductless systems come as single units (one indoor, one outdoor) or multiple-units (one outdoor, up to four or more indoor units). Working an entire house into a system with a single outdoor unit can create extra challenges. I opted for two outdoor units (one at the side and one at the back), with one connected to two upstairs and two downstairs rooms and one connected to two larger rooms upstairs. With multiple-unit systems, you do not always have control over the priority assigned to each indoor unit if you are trying to bring a number of cold rooms up to room temperature (though you can always run the system with one indoor unit in a room you want to heat up first on and all others off ). Once all rooms are close to the desired temperature, the systems tend to maintain these. Split/ductless systems sometimes had control units with less ability to program temperatures (24/7 thermostats with multiple setting times and temperatures) than
ducted heat pump systems. My own units use remote controls, so I can control on/off/temperature and set an on time, an off time or an on/off or off/on combination (but not on a repeated basis: I must reset each day). I have seen systems on the market with remarkable programmability, sometimes all built into the remote units available in each room. Usually, the total indoor unit capacity cannot exceed the rated output of the outdoor unit. I have a 36,000 BTU outdoor unit which is often on to heat the bedroom (9,000 BTU unit) and my home office (another 9,000 BTU unit). The two spare bedrooms (one now an exercise room) with two more units at 9,000 BTU are almost never used. It is now possible to have a system where the indoor unit size exceeds the outdoor capacity. All major rooms in my house are heated with my heat pump system. But two hallways and three washrooms are not; for these, I have either left my earlier baseboard heating in place or installed floor electrical heating. They are small spaces not requiring as much, so I wasn t that concerned. Can I have a hybrid system? Yes, but for a house where a system-wide ducting system is already present or being installed, it is usually possible to install a heat pump over a gas furnace, but the question is, if gas is cheaper than the heat pump for heat, why not just get a cheaper air conditioning unit instead? One answer would be to hedge against gas rising faster than electricity prices in the future (this solution makes more sense if the price difference between an AC unit add-in and a heat pump add-in is small). A mixture of a gas furnace/ducted and a heat-pump ductless system might work. A heat pump system might be used for the upper floor; for a distant room that is not well heated by an existing duct system; or which is difficult to include as part of a retrofit. Hot water heat pumps? There are heat pump systems that can heat water, with roughly the same cost per BTU considerations as the comparison between gas furnace and heat pump systems. If you have gas, I d suggest using this method, unless you have environmental concerns (i.e., think electricity is cleaner ), because it will be slightly cheaper in the near future. I have not seen a heat pump water system in operation, and suspect it will be more difficult to find an expert HVAC firm in Victoria to install one. Some of the newer heat pump water systems will handle multiple zones one can be used to heat the house s hot water while the other can be used for floor heating using water pipes. Again, buyer beware I don t think local firms have a lot of experience with this. Does my house have the electrical capacity? Some HVAC contractors will bring their own electricians. Others will ask you to get one and have electrical power ready at the site. You are adding electrical demand to your house. Paradoxically, you are using less electricity, but you still need more capacity because if ever electrical device in your house was turned on at the same time,
the demand would go up. Most Broadmead homes probably have the main panel electrical capacity to handle this, with 200 amp panels currently in place. I was able to add two 30 amp circuits for my two heat pump systems (totaling 72,000 BTU) while still keeping within the household total capacity. I could have decommissioned some of my house baseboard heaters, which now act as a probably-never-to-be-used backup should anything go wrong with my heat pumps. Without doing so, the cost of upgrading the service (including having BC hydro pull a new underground electrical cable to my house) might have been quite high. Consult a reputable electrician for information. Other considerations: municipal bylaws Outdoor units can be noisy, though, in my case, not so noisy that I can actually hear them from inside the house. The municipal noise bylaw restricts homeowners noise level at the property line so the further the heat pump unit is from a property line, the less likely there will be an issue. Take outdoor noise specs into consideration when comparing units.