HOUSING                                           PIH-57


                     Supplemental Heat for Swine

Sam L. Harp, Oklahoma State University
Raymond L. Huhnke, Oklahoma State University

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.*
                                       Supplemental heat/animal unit
                                   Inside     Slotted    Bedded/scraped
                                 temperature   floor          floor
                                     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           --
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-
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)

     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-

     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-

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.


     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

Table 3. Suggested use, location and control of  radiant  heaters
for swine.

Type and size        Use                            Location and number  

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  


Contd...Table 3.

Type and size        Radiant output         Control

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.

* 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)

Cooperative Extension Work in  Agriculture  and  Home  Economics,
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