Furnace fan controller

chadb · 12-29-12, 10:20 AM

I used to set my thermostat to 58 when I was gone 63 at night 68 morning/evening when I was home. Propane costs too much. My thermostat has been set to off for about 3 years now. I still spent too much using electric heaters so this year I gave them away. The upstairs bathroom is heated with a baseboard heater to 65 - 67. My son's room also has one and is kept about 68. I use a heated mattress pad in my room. The blower on the furnace stays on to circulate and the rest of the house is whatever the wood stove gets it too. Lately its been around 20 F outside at night and 34 in the day. Even though I haven't been getting up at night to put wood in its been about 63F when I wake up and get home from work. I measured the temp of the stove itself this morning at about 120 with enough coals left to restart a fire.

Daox · 12-29-12, 01:03 PM

So your furnace fan is going 24/7? Do you know how much power your furnace blower uses? When my furnace is on it is pulling at least 400 watts. If you run that all day that is almost 10kWh. You might consider putting a timer on it, or finding a way to reduce the motor's speed? Sizable gains to be had if that is the case!

chadb · 12-29-12, 01:29 PM

Yeah I have a lot of room for improvement in this old house. I've thought about the power usage of the fan. For now it's a huge improvement over the 2 -3 1500 watt heaters that used to run almost 24/7. I used to spend $350 - $550 a month during the winter on electricity. Before that I spent $250 a month electric and about $2,000 in one year for propane. So far this year $200 a month electricity and the wood I've burned up to now only cost me the gas for my truck to haul it and for the chainsaw I cut it with.

What I'd like to do is have the blower come on at a set temperature. It can already do that in heat mode. I just have to find a way to bypass the furnace trying to ignite and burn propane. Seems like it should be easy enough. Maybe I can spend one day figuring it out since I have a couple days off for the holidays.

Daox · 12-29-12, 01:47 PM

If I might poke around your business a bit, I think the best way to turn it on/off would be to setup a small controller for it. Perhaps we should start a new thread since its not on topic for this thread, but I'll outline the idea. Basically, you want two temperature sensors. One goes in a colder area of the house, and one in a known warm area. When the cold temperature sensor is X degrees cooler than the warm sensor, you turn the fan on to equalize the heat. Once it is within a degree or so, you turn it back off. Basically a thermal differential controller for your furnace blower. Something like this wouldn't be hard to setup or even buy for a relatively cheap amount, and would pay for itself very quickly.

chadb · 12-29-12, 01:56 PM

That would be perfect for my setup. My wood stove is in the kitchen and the living room on the other end of the house is the cold area I'm trying to get the heat to. At times it could be 85+ degrees in the kitchen and could be 60 in the living room without the furnace circulating. I'm just starting to poke around in electronics and I don't know much. Any help you can give on the idea would be greatly appreciated.

MN Renovator · 12-29-12, 02:16 PM

Quote:

Originally Posted by chadb

I used to set my thermostat to 58 when I was gone 63 at night 68 morning/evening when I was home. Propane costs too much. My thermostat has been set to off for about 3 years now. I still spent too much using electric heaters so this year I gave them away. The upstairs bathroom is heated with a baseboard heater to 65 - 67. My son's room also has one and is kept about 68. I use a heated mattress pad in my room. The blower on the furnace stays on to circulate and the rest of the house is whatever the wood stove gets it too. Lately its been around 20 F outside at night and 34 in the day. Even though I haven't been getting up at night to put wood in its been about 63F when I wake up and get home from work. I measured the temp of the stove itself this morning at about 120 with enough coals left to restart a fire.

The part about this that I would be most concerned about is that many houses have been constructed with an outdoor air intake designed to supply fresh air to the house. They are designed to exchange enough air when the furnace or a/c is operating for normal time periods. If you have one of these intakes, I would strongly consider adding a damper that shuts this when the furnace or air conditioner is off. ..or better yet run the intake into the basement with an air trap so that way your furnace gets the combustion air it needs without feeding the house with freezing air.

I'd rather blow the heat around with a box fan or two, those are about 100 watts a piece on high, lower at slower speeds. They move tons more air for the amount of power they consume.

Also if propane is more expensive for you to heat with versus using electric space heaters, you might want to consider a fairly efficient heat pump to replace your current air conditioner. You could save money throughout the year. This would be a much lower cost option on a monthly basis. Just be sure to get one that uses demand defrost instead of a timer and also be sure that any supplemental strip heat is done on a staged basis while the heat pump is allowed to continue running.

Daox · 12-29-12, 02:25 PM

I copied our posts over to a new thread.

There are numerous options for controller options. IMO the easiest is probably to go to the site below and buy their cheapest model which is $69 (or $77 with an enclosure). The relay is rated for 5A at 125V, so it can probably switch your furnace on or off by itself. You'll need a 12V power supply (wall wart) for it too.

myDTC Differential Temp Controllers and Outdoor Reset Control Store - Temperature Controllers

If you want to make a project out of it and learn some new stuff, I made my own arduino based thermal differential controller for a small project I did a while back. Its a bit more dinking around, but sometimes its fun to learn new stuff and figure it out yourself.

There are also some other DIY thermal differential controllers mentioned in this thread:
http://ecorenovator.org/forum/applia...ontroller.html

chadb · 12-29-12, 02:34 PM

mn renovator - thanks for the input. Unfortunately I don't have the budget for a heat pump. I have plans on doing some passive solar heaters, improving insulation, window shutters, etc. I will spend the little money and time I have on that stuff this spring/summer. Beating the price of firewood that comes from unwanted trees people give away for free is hard to do. I've also tried the box fans in the past and haven't been happy with the results or the noise of multiple fans. I recently installed a return duct directly above my wood stove (12 foot high ceiling, not close enough to the stove to be a safety issue) and this is working quite well.

Daox - thanks for the information, I'll spend some time researching. I like the idea of building one myself. I've been trying to convince myself to pick an electronic project to begin learning anyway.

chadb · 12-29-12, 02:40 PM

Here's what I've done so far for a temporary solution -

Unhooked white wire from W on thermostat. This is used to switch the heat system on when the set temperature is reached.

Unhooked green wire from G used to switch fan on and off.

Hooked green wire to W. Now when the temperature reaches setpoint my fan is turned on instead of the heating system.

Reasons Daox's solution is better:
1. If the fire in the stove dies out while I'm gone and both rooms drop below the setpoint I will just be blowing around cold air and wasting energy.

2. I don't currently have any propane but would like to be get some and be able to set the thermostat to say 50 degrees for when I'm away for extended amounts of time. My current solution doesn't allow me to do this.

Daox · 12-30-12, 01:25 PM

That sounds like a good idea if the thermostat is in your living room.

12-29-12, 10:20 AM	#1
chadb Lurking Renovator Join Date: Nov 2012 Location: Mt. Orab, OH Posts: 18 Thanks: 3 Thanked 0 Times in 0 Posts	Furnace fan controller I used to set my thermostat to 58 when I was gone 63 at night 68 morning/evening when I was home. Propane costs too much. My thermostat has been set to off for about 3 years now. I still spent too much using electric heaters so this year I gave them away. The upstairs bathroom is heated with a baseboard heater to 65 - 67. My son's room also has one and is kept about 68. I use a heated mattress pad in my room. The blower on the furnace stays on to circulate and the rest of the house is whatever the wood stove gets it too. Lately its been around 20 F outside at night and 34 in the day. Even though I haven't been getting up at night to put wood in its been about 63F when I wake up and get home from work. I measured the temp of the stove itself this morning at about 120 with enough coals left to restart a fire.

12-29-12, 01:03 PM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	So your furnace fan is going 24/7? Do you know how much power your furnace blower uses? When my furnace is on it is pulling at least 400 watts. If you run that all day that is almost 10kWh. You might consider putting a timer on it, or finding a way to reduce the motor's speed? Sizable gains to be had if that is the case! __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

12-29-12, 01:47 PM	#4
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	If I might poke around your business a bit, I think the best way to turn it on/off would be to setup a small controller for it. Perhaps we should start a new thread since its not on topic for this thread, but I'll outline the idea. Basically, you want two temperature sensors. One goes in a colder area of the house, and one in a known warm area. When the cold temperature sensor is X degrees cooler than the warm sensor, you turn the fan on to equalize the heat. Once it is within a degree or so, you turn it back off. Basically a thermal differential controller for your furnace blower. Something like this wouldn't be hard to setup or even buy for a relatively cheap amount, and would pay for itself very quickly. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

12-29-12, 02:25 PM	#7
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	I copied our posts over to a new thread. There are numerous options for controller options. IMO the easiest is probably to go to the site below and buy their cheapest model which is $69 (or $77 with an enclosure). The relay is rated for 5A at 125V, so it can probably switch your furnace on or off by itself. You'll need a 12V power supply (wall wart) for it too. myDTC Differential Temp Controllers and Outdoor Reset Control Store - Temperature Controllers If you want to make a project out of it and learn some new stuff, I made my own arduino based thermal differential controller for a small project I did a while back. Its a bit more dinking around, but sometimes its fun to learn new stuff and figure it out yourself. There are also some other DIY thermal differential controllers mentioned in this thread: http://ecorenovator.org/forum/applia...ontroller.html __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

12-30-12, 01:25 PM	#10
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	That sounds like a good idea if the thermostat is in your living room. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

12-29-12, 01:29 PM	#3
chadb Lurking Renovator Join Date: Nov 2012 Location: Mt. Orab, OH Posts: 18 Thanks: 3 Thanked 0 Times in 0 Posts	Yeah I have a lot of room for improvement in this old house. I've thought about the power usage of the fan. For now it's a huge improvement over the 2 -3 1500 watt heaters that used to run almost 24/7. I used to spend $350 - $550 a month during the winter on electricity. Before that I spent $250 a month electric and about $2,000 in one year for propane. So far this year $200 a month electricity and the wood I've burned up to now only cost me the gas for my truck to haul it and for the chainsaw I cut it with. What I'd like to do is have the blower come on at a set temperature. It can already do that in heat mode. I just have to find a way to bypass the furnace trying to ignite and burn propane. Seems like it should be easy enough. Maybe I can spend one day figuring it out since I have a couple days off for the holidays.

12-29-12, 01:56 PM	#5
chadb Lurking Renovator Join Date: Nov 2012 Location: Mt. Orab, OH Posts: 18 Thanks: 3 Thanked 0 Times in 0 Posts	That would be perfect for my setup. My wood stove is in the kitchen and the living room on the other end of the house is the cold area I'm trying to get the heat to. At times it could be 85+ degrees in the kitchen and could be 60 in the living room without the furnace circulating. I'm just starting to poke around in electronics and I don't know much. Any help you can give on the idea would be greatly appreciated.

12-29-12, 02:34 PM	#8
chadb Lurking Renovator Join Date: Nov 2012 Location: Mt. Orab, OH Posts: 18 Thanks: 3 Thanked 0 Times in 0 Posts	mn renovator - thanks for the input. Unfortunately I don't have the budget for a heat pump. I have plans on doing some passive solar heaters, improving insulation, window shutters, etc. I will spend the little money and time I have on that stuff this spring/summer. Beating the price of firewood that comes from unwanted trees people give away for free is hard to do. I've also tried the box fans in the past and haven't been happy with the results or the noise of multiple fans. I recently installed a return duct directly above my wood stove (12 foot high ceiling, not close enough to the stove to be a safety issue) and this is working quite well. Daox - thanks for the information, I'll spend some time researching. I like the idea of building one myself. I've been trying to convince myself to pick an electronic project to begin learning anyway.

12-29-12, 02:40 PM	#9
chadb Lurking Renovator Join Date: Nov 2012 Location: Mt. Orab, OH Posts: 18 Thanks: 3 Thanked 0 Times in 0 Posts	Here's what I've done so far for a temporary solution - Unhooked white wire from W on thermostat. This is used to switch the heat system on when the set temperature is reached. Unhooked green wire from G used to switch fan on and off. Hooked green wire to W. Now when the temperature reaches setpoint my fan is turned on instead of the heating system. Reasons Daox's solution is better: 1. If the fire in the stove dies out while I'm gone and both rooms drop below the setpoint I will just be blowing around cold air and wasting energy. 2. I don't currently have any propane but would like to be get some and be able to set the thermostat to say 50 degrees for when I'm away for extended amounts of time. My current solution doesn't allow me to do this.