How to run A/C Fan without the compresser

[New Hampshire Jim]

My son has Installed a Harman Advance Insert in his fireplace. On the floor right next to It Is the cold return for his central A/C. We were thinking that In the winter If we could run the unit without running the compressor It would move hot air from the stove room and distribute It to the rest of the house. Has anyone done this ? Without burning up the compressor or other parts? and how easy Is It to do. My son Is a Mechanical Engineer but I am a retired Old Fart and Its my Idea. Any help will be appreciated. Thanks
JimH

 

[AK13]

Yes, it should be doable but its impossible to tell you how without seeing the wiring for the A/C unit. It won't damage the compressor. A typical programmable thermostat has RGYW terminals. Y is cooling. G is fan. W is heat. My guess is that his A/C unit has a terminal strip that would allow you to run the wire from "G" on the thermostat to control the fan, but its possible that he'd need to rewire the A/C unit slightly.

That said, I don't think that the central A/C unit will do a very good job distributing heat. I have a central furnace and heat with wood and don't bother running my central blower because it really doesn't seem to distribute heat very well. The return is going to be pulling cooler air off the floor, not the nice hot air out of the insert. He could try it, but my guess is that it isn't going to work all that well.

 

[Ashful]

If all ductwork and (most importantly) the air handler is installed within the heated / insulated envelope of the building, then this can work to some degree. If the ducts or air handler are installed in an unheated attic or basement, then the relatively low maximum heat output of your pellet stove will typically not overcome the heat losses of moving the air thru the cold ducts and air handler.

As to how to do it, system controls vary, but on traditional / old-skool systems there is a third (usually green) wire running from the control panel to the thermostat for each zone. This wire is for the fan control. Most thermostats include a manual fan override, which will energize the fan. Trouble is, many of those thermostats require you to set the mode to "heat" or "cool", before they will enable the fan control. This can be easily overcome by setting the thermostat to "heat", but setting the temperature well below current room temperature, to prevent the system from cycling. Then you can manually energize the blower from the thermostat.

 

[Jocko1]

Tried this but it didnt work since air handler was in cold attic

 

[bwise.157]

I tried this last winter, but didn't see any benefit. I pulled the cooling wire off in my programmable Tstat, flipped the AC unit breaker off, and used my central air system in cooling mode during the winter. The fan in my furnace would run when the temps in the house warmed up. It would conversely shut off when the house cooled down. The upstairs rooms didn't warm up any more than when I used a box fan to move air. Actually, the box fan method worked much better and consumed much less electricity.

 

[Jocko1]

I second box fan method. Blow air from cold room into warm room on the floor. It works great

 

[Phoenix Hatchling]

I did this this past winter and made a BIG difference. Rooms furthest away from the living room where the stove resides were much warmer than previous years. As an additional bonus, change out the filter a couple times in the season and see how much dust is taken out of the air! Yuck. Make sure that the vents are well insulated if they are in the attic though. Mine has eight inches thick of insulation surrounding all the lengths.

 

[macattack_ga]

I switch the separate breaker to my A/C compressor off during the winter. Then I set the thermostat to “cool” (w/o compressor) to 80 during the winter. When the stove gets things warm, the HVAC moves some of the heat around (but not much).

 

[Phoenix Hatchling]

I simply turn the Fan from Auto to On, and leave the rest of the system off. The compressor is shut off during the winter anyhow.

 

[rowerwet]

My dad has his cold air return above his pellet stove, the oil co put a thermostat on the wall to turn on the blower when the stove area hits 70. It works, but the fan runs non stop, you put your hand over the heat vents and feel cold air though, as the air coming out is only 70 F. The house stayed near 68 all winter that way.

 

[Ashful]

I simply turn the Fan from Auto to On, and leave the rest of the system off. The compressor is shut off during the winter anyhow.

View attachment 135491

That's what I was explaining in my original post, but some systems do now allow the fan to energize, unless you're set to heat or cool modes. Most often, this happens when you have any system other than a heat pump (eg. boiler for heat with separate AC), since the thermostat is then set for a mode in which the fan relay only works when the thermostat is set to cool mode. In fact, some thermostats have separate terminals for heating and cooling fans, with a jumper between them, designed to be removed when you have separate hot air (eg. oil furnace) and cold air (AC) systems. Every house in which I have lived since 1981 has in fact had separate heating and cooling systems, and this work this way.