Are your furnaces ready for fall conditions?

Yesterday I was involved in a ventilation workshop at Adams, MN, located just east of Austin. Crops in the region were hit to a varying degree by the early morning freeze/frost, the impact of which remains to be sorted out in the market place.

With the first cold morning of the season, I’m pretty sure some of the swine nursery rooms and maybe even a few farrowing rooms had some heaters turn on. At the workshop we had a good discussion with growers and owners about the basics of furnace management.

All of us recognize the need for supplemental heat in production facilities and make major investments in furnaces, heat lamps and mats for farrowing rooms and propane brooders for weaned pigs in wean-finish facilities. At the same time, all of us complain about the propane and electric bills associated with the use of these devices.

As we go into the winter heating season, there are a couple of things to keep in mind regarding furnace management that have a big impact on propane usage and pig comfort. If you have furnaces with a variable output valve (LBWhite Guardian series, PSI or the new HiredHand series), 100% of these furnaces should have the valve turned to the low setting at this time of year.

Furnaces are sized for the maximum heat output required in January, not the minimal heat requirement of October and November mornings. As such, they are very much oversized relative to the needs of the space being heated. A furnace is big enough if it turns off, something we all too often forget. Along with this, the longer a furnace runs per burn cycle, the more uniform the temperature in the facility. This basic understanding of furnace sizing and use supports reducing heat output from oversized furnaces at this time of year.

When furnaces are oversized, all too often operation of the furnace leads to an increase in the ventilation rate (speeding up of the variable speed stage 1 fan) after the furnace(s) turn off. It is not uncommon to have 2 or more F degree rise in room temperature as measured by the ventilation controller probes after furnaces shut off.

At yesterday’s workshop, we advised attendee’s to start with shutting furnaces off 2F below the temperature at which the stage 1 fan runs faster. For most (but not all) controllers, this means the furnace should shut off 2F below the set point. When the furnace runs and shuts off, the room temperature should NEVER get to set point – temperature rise should stop about 0.2F below set point or the 0.3F below the temperature at which the variable speed fan increases speed. Anytime the fan increases speed in response to a furnace adding heat to an animal space, propane expense will be increased.

What are reasonable targets for propane expense/use? I get asked this all the time, and there aren’t very many data sets available for what is ‘average’? In general, the target for wean-finish facilities should range from 2 gal/pig space/year for central Iowa to 2.5 gal/space/year for Minnesota producers in the Willmar area. Many grow-finish facilities report less than 0.5 gal/space/year usage. Unfortunately, I don’t have any reliable numbers for swine nurseries that I can share as reasonable targets.

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