So when it was -15F and windy here a few nights ago I awoke to a house that was at 59F. We have the thermostat programmed for 62F overnight so it was not a big deal. The OWB had burned through the wood I put in before going to bed and the water temperature was down to 118F. Plenty of coals to get another load started and in a short time the water was right back up to 175F. The furnace fan continued to run trying to bring the house up to temperature. Slowly, over the next 6-7 hours, the house temperature was raised from 59F to 68F. In that time the outside temperature increased to -5F, so really the house was only tracking to the increase in the outside temperature. The OWB was cycling on and off between 165F and 175F so it seems it was able to keep up, but the warm air distributing through the ductwork was only enough to maintain the house temperature.
I'm thinking that would mean that running the furnace on propane would have meant a 100% duty cycle - in other words A LOT OF PROPANE! Looking at a few charts it seems that a standard house the size of mine in Michigan should have a 120,000 Btu furnace. With the 25' cathedral ceilings with only a few inches of foam insulation and some big windows it should probably be a bit higher. We only went one winter heating with propane here so I really don't know how the furnace has performed, but it's only about 100,000 Btu. Actually never had an issue with it so it did seem adequate.
The rated maximum outlet air temperature of the furnace is 175F, so I'm probably a bit less than that with the OWB heat exchanger only getting to a maximum of 175F on the water side. I could have bumped the water temperature up more - I'm kinda hoping I don't have to do that any time soon though as I've had quite enough of the below zero temperatures for a while. I did find it interesting that the water could be kept up the temperature with the OWB without appreciably raising the air temperature in the house. At -15F I'm only getting a 6-7 hour burn time when fully loaded.
I'm thinking that would mean that running the furnace on propane would have meant a 100% duty cycle - in other words A LOT OF PROPANE! Looking at a few charts it seems that a standard house the size of mine in Michigan should have a 120,000 Btu furnace. With the 25' cathedral ceilings with only a few inches of foam insulation and some big windows it should probably be a bit higher. We only went one winter heating with propane here so I really don't know how the furnace has performed, but it's only about 100,000 Btu. Actually never had an issue with it so it did seem adequate.
The rated maximum outlet air temperature of the furnace is 175F, so I'm probably a bit less than that with the OWB heat exchanger only getting to a maximum of 175F on the water side. I could have bumped the water temperature up more - I'm kinda hoping I don't have to do that any time soon though as I've had quite enough of the below zero temperatures for a while. I did find it interesting that the water could be kept up the temperature with the OWB without appreciably raising the air temperature in the house. At -15F I'm only getting a 6-7 hour burn time when fully loaded.