HOUSING PIH-57
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Supplemental Heat for Swine
Authors
Sam L. Harp, Oklahoma State University
Raymond L. Huhnke, Oklahoma State University
Reviewers
John and Bonnie Korslund, Eagle Grove, Iowa
Gerald L. Riskowski, University of Illinois
Mark E. Smith, Jackson, Tennessee
Supplemental heat is required if the animals do not generate
enough heat to keep the room temperature at an acceptable level.
The amount of supplemental heat needed depends on many factors
such as pig size, building insulation level, desired room tem-
perature and the outside temperature. The ventilation system also
affects supplemental heat requirements. In a well-insulated
animal facility, as much as 90% of the heat produced in the
building is exhausted through the ventilation system. Because of
the difficulty in determining the actual supplemental heating
needs, estimates are made to size heaters. Table 1 gives the
estimated requirements for typical swine facilities in North Cen-
tral United States.
In some buildings, such as the farrowing house where supple-
mental heat is be considered as part of the regularly used, per-
manent heating systems should be considered as part of the total
environmental control system. Where permanent heating systems are
not cost effective, a temporary heater can be moved into the
building for several days to get through a cold spell or when the
building is partially loaded. Whether you use a permanent or
temporary heating system depends on many factors including loca-
tion in the United States, animal size, and management scheme.
Table 1. Sizing supplemental heaters.*
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Supplemental heat/animal unit
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Inside Slotted Bedded/scraped
temperature floor floor
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o F - - - - - Btuh/unit - - - - -
Sow and litter 80 4,000 --
70 3,000 --
60 -- 3,500
Prenursery pig (12-30 lb) 85 350 --
Nursery pig (30-75 lb) 75 350 --
65 -- 450
Growing-finishing pig (75-220 lb) 60 600 --
Gestating sow/boar 60 1,000 --
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Source: MWPS-34, Midwest Plan Service Heating, Cooling and
Tempering Air for Livestock Housing.
*Note: The supplemental heat recommended in Table 1 provides
reserve heater capacity to handle heating needs when only a few
animals are present. Additional zone heat may be needed for
young animals.
Example: A 10-sow farrowing room kept at 70o F requires about 10 x
3,000 = 30,000 Btuh heating capacity.
Unit Heaters
A unit heater has all the components assembled into one con-
tainer and needs only to be hung in the building and connected to
a source of fuel and electricity (see Figure 1). The basic unit
heater consists of a fan, either propeller or centrifugal, and a
heating element. Some unit heaters are equipped with air intake
filters, directional discharge louvers, and automatic temperature
controls. Unit heaters are generally installed overhead, elim-
inating the need for using valuable floor space. Most unit
heaters use 100% recirculated air.
There are several types of heating elements used with unit
heaters. For swine buildings, however, the direct-and/or
indirect-fired gas burners and electric heating elements are the
most common. A hot water element is another option, especially in
farrowing or nursery buildings where under-floor hot water heat
is used.
Dust can be a problem with unit heaters because they use
recirculated air. The amount of dust in the air depends on
management and the type of feeding system. If the circulated air
is filtered, a centrifugal blower works better than a propeller
fan against the higher static pressure caused by the filter.
The size and number of unit heaters needed depend on the
heat requirement and floor area of the particular swine building.
As an example, a 24-sow farrowing room kept at 70o F located in
central Illinois would need about 72,000 Btuh (Btu per hour) of
supplemental heat (24 times 3,000 from Table 1). Assuming a
heater efficiency of 80%, heater size would be approximately
90,000 Btuh (72,000 divided by 0.80). This heat could be provided
using one large unit or two smaller heaters at about 45,000 Btuh
each. Two heaters probably would give better heat distribution
than if just one single unit was installed.
Table 2. Typical efficiencies for some common heating sys-
tems.
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Solid Fuel (coal and wood) Furnace 40-60%
Gas or Oil Furnace 50-95%
Electric Resistance 100%
Air-source Heat Pump 150-250% (COP = 1.5 to 2.5)
Ground-source Heat Pump 250-300% (COP 2.5 to 3.0)
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The thermal efficiency (Table 2) of fuel burning heaters is
defined as the amount of useful heat produced divided by the
heating value of the fuel consumed. Thermal efficiency is usu-
ally less than 100% due to incomplete combustion of the fuel and,
for vented heaters, heat lost due to venting. Venting of fuel
burning equipment is necessary to remove the products of combus-
tion from the space. If unvented heaters are used, increase the
ventilating rate by 2.5 cfm for each 1,000 Btuh of heater capa-
city to prevent buildup of moisture and poisonous combustion
gases. When vented heaters are used with negative pressure venti-
lation systems, use fan powered vents with a vent damper.
Thermal efficiency of electric heat pumps is called coeffi-
cient of performance (COP) and is defined as useful heat output
divided by heat equivalent of the electrical energy required to
operate the system. Another term commonly used for heat pumps is
heating season performance factor (HSPF) and is merely the COP
multiplied by a constant of 3.413. Heat pumps can have efficien-
cies greater than 100% because they do not convert electrical
energy to heat. Instead, they use this energy to "pump" heat from
the source (typically air or ground) to the space being heated.
Efficiency is highly dependent upon source temperature. Low
source temperature results in correspondingly low efficiency.
The term "throw" relates to the horizontal distance that the
warm air is projected from the heater. If the 90,000 Btuh and
45,000 Btuh heaters in the previous example have about the same
throw, the two smaller units would probably produce a more uni-
form temperature throughout the house compared to the larger
heater. Another option would be for the unit heater, used in com-
bination with some type of simple duct air tube system, to dis-
tribute the heated air along the length of the house. Another
approach would be to divide the farrowing house into two smaller
rooms with one 45,000 Btuh heater per room.
If the room does not have an air distribution system, a more
uniform temperature distribution is obtained when the unit heater
is installed to blow along the coldest wall. The warm air will
intercept the cold drafts from that wall. Likewise, a heater
should discharge heated air across a cold air baffle inlet or
series of ceiling inlets to provide for better air mixing. Where
several heaters are used, they should be arranged so that the
discharge from each heater helps create a general circulatory
motion of air within the room. Ceiling-mounted units with the
outlet louvers properly set should deliver the heated air to the
occupied zone (pig level) at acceptable temperatures and veloci-
ties.
Because dust and high humidity are often a problem in swine
units, a regular maintenance schedule must be established.
Inspect heaters weekly for dust build-up. The amount and fre-
quency of cleaning will depend on your particular heater and room
conditions. The heating elements, fan blades and output louvers
are often cleaned by brushing or blowing with high-pressure air.
Whenever the building is cleaned with a high-pressure water or
steam cleaner, the heater also should be cleaned. Check the
heater service manual for recommended cleaning methods. CAUTION:
Totally disconnect the electric power before cleaning, and be
sure no moisture remains in the electrical boxes before restoring
the power. The fan motor should be totally enclosed. All electri-
cal wiring and fuel line connections should be inspected annu-
ally.
Make-up Air Heaters
Most unit heaters use 100% recirculated air; whereas, most
make-up (ventilation) air heaters use 100% outside air. Since the
make-up air heater heats air entering the building, some air must
also be exhausted or removed from the building. Make-up air
heaters are generally located outside of the space or building
they are heating.
Make-up air heaters are sized either by: 1) rate of air flow
through the unit, 2) maximum energy input to the heating element,
or 3) both methods. Typical farm application sizes range from
about 600 to 2,000 cfm with gas as the usual fuel choice. Most
heaters have a potential of over 120o F temperature rise for the
air passing through the heater at maximum fuel input.
Some gas make-up heaters burn the gas directly in the air
stream entering the building resulting in all the products of
combustion entering the building along with the heated air. If
direct-fired units are used, add at least 2.5 cfm to the cold
weather ventilation rate for each 1,000 Btuh of heater capacity.
Air distribution must be considered when using make-up air
heaters. When the make-up air heater is operating, most of the
air will enter at one point instead of being uniformly distri-
buted around the building. This can cause uneven air temperatures
within the building.
Therefore, an air distribution system such as a fan-tube or duct
often is used to ensure good air mixing and more uniform air tem-
peratures. Ducts near heaters need to be fireproof.
Controls
Careful consideration must be given to the safety controls
of heating equipment. For gas heaters, some type of gas and fan
shut-off is needed if ignition by the electrical igniter does not
occur within approximately one minute. Also, some type of manual
reset flame sensor is needed that will shut down the unit in case
the gas supply is exhausted. A sail switch, sensitive to the flow
of air, will make sure that the blower is operating or that air
is passing through the unit before the ignition circuit is
activated. If the air flow stops after activation, the main gas
valve should close. There also should be a high-temperature
switch to shut down the unit if the temperature at the discharge
and/or burner is too high. The usual electrical safety equipment,
such as circuit breakers, should be available to protect the
blower motor from possible overload damage.
A minimum level of ventilation should be maintained in a
swine building at all times. Therefore, it is not uncommon for
the heating system to operate when the minimum ventilation fan is
operating. Thermostats that control fans (except the minimum fan
rate) should be set a minimum of 4o F above the heater thermostat
setting. The preferred method is to have the heater and fan con-
trols interlocked or operated by the same controller. If the
thermostats are not properly set, ventilation fans that control
temperature may run when the heater is operating, thus wasting
energy. When several persons are involved in a swine operation,
only one should have the responsibility of adjusting the heater
control.
Table 3. Suggested use, location and control of radiant heaters
for swine.
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Type and size Use Location and number
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Gas, Catalytic Farrowing house Hung over two adjacent
or Ceramic Core pig creep areas intentionally on or off.
4-6 MBH*
10-12 MBH Nursery and 5 to 6 ft. above the
growing/finishing sleeping area; one
heater per 100 sq ft
of sleeping area
Electric 250 W bulb Farrowing house One per pig creep
1-2.5 kW Nursery and growing/finishing 5-6 ft. above
the sleeping area
Gas or electric Emergency situations and Near ceiling; as many
partially loaded buildings. as deemed necessary
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Contd...Table 3.
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Type and size Radiant output Control
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Gas, Catalytic 30-35%** Uncontrolled:
or Ceramic Core intentionally on or off.
4-6 MBH*
10-12 MBH 40-45% Mounted air
set at 35-40o F in open
front building, 50o F in
closed building.
(Should have automatic
gas shut-off in case of
pilot light failure.)
Electric 250 W bulb 70-75% Uncontrolled:
intentionally on or off.
1-2.5 kW 75-80% Radiant receptive thermostat
advisable because of small
amount of air heating.
Settings similar to gas.
Gas or electric Near ceiling;as many Air thermostat set at
as deemed necessary 45-55o F or manual
adjustment as necessary.
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* Thousand Btuh input rating.
** 30-45% of the input energy to gas heaters is given off as
radiant heat. The remaining 50-65% of the energy heats the air.
For electrically powered heaters the percentage of radiant heat
output is typically in the range of 70-75% with 25-30% heating
the surrounding air.
Radiant Heaters
Radiant heaters have a special advantage because the heat
produced is transmitted by radiation, like light rays, rather
than heating the air. Therefore, they can be fairly effective in
open front buildings. Radiant heater types range from heat lamps
for zone heating to fan-driven pipe units for providing heat in
an entire building.
Radiant heat is transferred to an object when it strikes the
object in its path. Thus, radiant heat shining on a pig transfers
the heat directly to the animal without heating the air. This
allows the animal to be comfortable even though the surrounding
air, by itself, is too cool for comfort. Comfort can be provided
without heating all the building air. Therefore, this allows a
dual environment in a farrowing house where the thermostat can be
set to maintain a 60o F temperature for the sows, and radiant heat
can be added to the pig creeps to provide an 80 to 85o F
equivalent environment for the small pigs (Table 3v).
Creep area heating requires a localized high temperature
source which is generally supplied by electrical heat lamps or
gas-fired radiant heaters. If the floor is heated in a farrowing
creep area, provide a 250 watt (852 Btuh) overhead heat lamp for
the first few days after farrowing. If no floor heat is used,
provide 2,200 Btuh of overhead radiant heat per litter. This is
especially important in cold climates where heat lamps may not be
enough. Make sure the radiant heat is heating only the creep area
and not the sow.
Heat lamps are a potential fire hazard if not handled prop-
erly. Suspend lamps on chains and make the lamp cord at least 12
in. shorter than the floor-to-ceiling height, so it unplugs if
the lamp drops to the floor. For pigs, mount lamps at least 30
in. above pen floors and 18 in. above creep floors. Place no more
than seven 250 watt heat lamps on one 20 amp circuit. Consider
manual or automatic voltage controllers to regulate heat lamps
when full wattage is not required.
Gas catalytic radiant heaters are flameless and have rela-
tively low surface temperatures. Catalytic heaters are usually
not thermostatically controlled, which makes them less efficient.
They do not require gas flues if the room is properly ventilated.
Radiating surfaces of catalytic heaters must be kept clean to
maintain heating efficiency.
Floor Heat
Floor heat is used primarily for localized heating. Common
floor heaters are electric resistance cables or hot water pipes
buried in the concrete floor. For more detailed information on
floor heating systems see MWPS-34, Heating, Cooling and Tempering
Air for Livestock Housing, Midwest Plan Service.
Move-in Heaters
The greatest need for temporary heating generally occurs
when a building is under stocked, perhaps at the start or end of
a farrowing or nursery cycle, or when there are only a few
animals in a large pen. A sudden cold spell also could require
some type of quick, temporary heat.
Most heaters moved into a building for temporary heating are
direct-fired gas or oil. These heaters have their own fuel supply
in an accompanying tank and only 115 volt power is needed for fan
and control operation. No flue is necessary if the room is prop-
erly ventilated. Sizes are available from about 30,000 Btuh to
100,000 Btuh.
The operating thermostat is usually located on the unit
which will cause greater temperature fluctuations within the
building. It is difficult to coordinate such a unit with the nor-
mal ventilation controls to keep the two from acting against each
other. Any unit employed in an animal shelter should have some
type of flame-out control that will automatically shut off the
fuel supply if the flame goes out for any reason. Loss of electr-
ical power should cause a full shut-down of the burner. Continual
use of move-in heaters in poorly ventilated farrowing rooms can
cause an increase in the incidence of stillbirths.
Air Tempering
Several methods, such as heat exchangers, solar walls, and
earth tubes, are being used to temper the air before it enters a
building. Warmed-air tempering systems help most in small animal
housing because they reduce drafts by improving air distribution,
providing higher temperature ventilating air, and enhancing warm
and cold air blending.
Warmed air tempering also simplifies air inlet management.
Tempered air is warmer and less dense, it is thrown farther into
a room, mixes better with room air before entering the animal
zone, and reduces drafts. Although some tempered air systems
reduce heating and sometimes cooling requirements, it is diffi-
cult to justify their purchase on energy savings alone.
Warmed tempered air systems usually provide cold weather
ventilation. Use a conventional ventilating system for mild and
hot weather ventilation. Switch from tempered to outside air when
the outside air temperature is high enough so animals are not
chilled. For more detailed information on floor heating systems
see MWPS-34, Heating, Cooling and Tempering Air for Livestock
Housing Midwest Plan Service.
Heat Exchangers
Heat exchangers are designed to move heat from the exhaust
air to the intake air. One type of heat exchanger is a parallel
plate unit in which exhaust and intake air are separated by thin
plates. These units can reclaim from 40 to 60% of the heat nor-
mally lost in the exhaust air. However, they can have problems
with the accumulation of dust, moisture and freezing. Heat
exchangers should include methods for easy cleaning and defrost-
ing. For more detailed information, see PIH-124, Heat Exchangers
in Swine Facilities.
Solar Energy
Because the sun is free and provides a readily available and
endless source of energy, it seems to be a very attractive energy
source for swine facilities. Some swine facilities already make
use of some solar collection by allowing ventilation air in the
winter to enter through the attic of the building.
Solar systems for swine facilities can be either a passive
or active type. Passive systems are a combination of south-
facing windows and a proper roof overhang which allows the build-
ing to collect the solar energy. Active systems require methods
for collecting and transferring solar energy. Active systems may
allow for heat to be stored in one location and used elsewhere.
Without a method of storage, an active system may provide
more solar energy than necessary during clear days and not enough
heat energy at night. See PIH-90, Solar Heating in Swine Build-
ings for more detailed information.
Earth-Tube Systems
Earth-tube heat exchangers use soil as a heat sink or source
for tempering the ventilating air. Depending on the season, air
is heated or cooled as it is drawn through a buried tube. The
temperature 7 to 10 feet underground is nearly constant
throughout the year.
Both soil characteristics and air-tube parameters affect the
performance of the system. Soil characteristics include soil
type, moisture content, and water table elevation. Air-tube
parameters include diameter, length, depth of placement, spacing,
flow rate, and the shape of the tube. Typically, an 8 in. to 12
in. diameter non perforated corrugated plastic drainage tile is
used because it is readily available and inexpensive. The corru-
gations increase the heat-transfer rate. For more detailed infor-
mation, see PIH-102, Earth Tempering of Ventilation Air.
Fuel Selection
The choice of fuel used in swine buildings depends on avail-
ability, price and special requirements. The main sources of
energy in most regions of the United States are propane, natural
gas and electricity. The relative availability of different fuels
may change in coming years, especially in local situations.
Therefore, consider long-term fuel supplies before making final
decisions about equipment.
The nomograph in Figure 2 can be used to estimate cost per
million Btu's of the heat supplied. To use the nomograph you
first need to know the type of heating system and its efficiency.
To estimate the cost of heat you must draw a straight line from
the cost per unit of the energy source through the heating system
efficiency scale to where it crosses the heat cost scale. For
example, an L.P. gas furnace with an efficiency of 80% and a fuel
cost of $0.80 per gallon would result in a heat cost of about
$11.00 per million Btu's. This nomograph also can be used to com-
pare heating costs for different types of heating systems and
fuels. To estimate the cost of heating with L.P. gas use scales
1, 3 and 5; for natural gas use scales 2, 3 and 5; for fuel oil
use scales 1, 4 and 5; for electric resistance and heat pumps use
scales 7, 6 and 5.
The cost of operating electric heat lamps or noncontrolled
gas-fired radiant heaters in a farrowing house is easily deter-
mined on an hourly use basis because the rate of energy consump-
tion is constant. A 250-watt heat lamp uses 1/4 kWh during each
hour of use. If electricity costs $0.08 per kWh, then the cost of
operation is $0.02 per hour or $0.48 per day. A 4,000 Btuh gas-
fired radiant heater uses slightly over 1 gal. of propane per day
and operating cost at $0.80 per gal. is about $0.03 per hour or
$0.80 per day.
Application Suggestions
Proper control of any heating system is necessary both from
an economic standpoint and for safety. Thermostats for unit
heaters and make-up air heaters should be hung low but still
within easy visual range. They should be located so as not to be
biased by the sun, animal mass, or by the output from nearby
heaters. When using small radiant heaters or some solid fuel
heaters, the operator usually must assume the task of turning
them on and off as needed.
All gas lines and/or gas heaters should have safety shut-off
valves. If the gas supply is interrupted, all valves should close
and require manual resetting unless automatic electric ignition
is provided for the heater. Small gas radiant heaters usually do
not have pilot lights and safety shut-off valves and thus need to
be closely monitored by a reliable operator.
Electrical wiring in and to the swine buildings must be of
adequate size if electrical supplemental heaters are used. Cir-
cuit load capacity is determined by the wire size used and not by
the size of the fuse that could be placed in the fuse box. Any
changes made in the electrical system should be done by someone
capable of determining safe circuit loads. For more detailed
information, see PIH-110, Electrical Wiring for Swine Buildings.
Reference to products in this publication is not intended to be
an endorsement to the exclusion of others which may be similar.
Persons using such products assume responsibility for their use
in accordance with current directions of the manufacturer.
List of Figures
Figure 1. Cross section view of a typical unit heater.
Figure 2. Nomograph for estimating heat cost.
REV 6/92 (7M)
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Cooperative Extension Work in Agriculture and Home Economics,
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culture Cooperating. H.A. Wadsworth, Director, West Lafayette,
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