Oil/heat pump dual energy issue

Problems related to residential installations.

Oil/heat pump dual energy issue

Postby carl333 » Sun Feb 13, 2011 10:50 am

I just had my heat pump replaced (Lennox) which is used in combination with my oil furnace. Here's the issue.

When ny heat pump goes into defrost mode, the oil furnace kicks in for 30 seconds then shuts off and I feel cold air from the registers for a couple of minutes or I would guess until the defrost cycle is complete on the heat pump. This happens perhaps once every 2-3 hours. Is it ok for the oil furnace to kick in several times a day for 30 seconds and then blow out? Is it possible that the defrost cycle time on the HP is only 30 seconds? I live in Montreal so hence our cold climate.
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- Oil/heat pump dual energy issue

Postby 4ftBanger » Sat Feb 19, 2011 9:12 am

I'd be a little concerned about the oil furnace short cycling. A 30 second burner cycle likely doesn't give the furnace a chance to establish a clean flame and certainly doesn't heat the chimney & flue up to establish proper draft. Unless you have a very efficient and well maintained oil furnace, over time short cycling could possibly lead to sooting and creosote build-up.

I would expect the furnace to run through the entire defrost cycle. The defrost cycle time depends on the outdoor coil temperature, but in northern climates would probably be at least a minute and a half or so... maybe more. - If the furnace isn't staying on, and you feel cold air, you may have a wiring issue or a problem with the defrost board in the heat pump or possibly some time delay built into the oil furnace control. I'd recommend you have it evaluated to make sure everything is working properly.

I've also installed a holding relay on oil boilers before. This is a control consisting of a couple of relays and a time delay to give the burner a minimum on time of around 3 minutes.
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