Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
Adjusting the blower on a hot air furnace?
I have a furnace that was replaced over the summer. Now that the heat is used more, I can tell that I am having a problem with the hot air blower (and maybe the furnace) short cycling.
Here's the setup:
1. oil fired, hydronic furnace in a three zone house. 2 zones are hydronic baseboard. The third zone is a hot air plenum supplied by the boiler.
2. The hot air plenum is controlled by a thermostat and an aquastat. The thermostat is setup to call for heat to the plenum when the living room temps are too cold. The aquastat turns the blower fan on and off based on plenum water temps.
3. The boiler is set to "cold start" meaning the temps will drop to room temps when heat is not needed.
The problem:
When the hot air zone initially calls for heat, the furnace will kick on and after a couple minutes so will the blower. On this initial start up of the blower, it will usually short cycle. By this, I mean the blower will turn off after only a couple minutes. Then, it will turn back on. This process of the blower and the furnace making short cycles will repeat until the temperature has risen enough that the thermostat stops calling for heat.
What adjustments do I need to make so stop the short cycling?
4 Answers
- ?Lv 52 years ago
Check the pressure of the water in the boiler.Little or no pressure may be causing low circulation.
- yLv 72 years ago
The aquastat turns the blower fan on and off based on plenum water temps, unless you are going to maintain the boiler temp as opposed to the cold start. You already know which control is creating the on/off blower cycle. Adjusting it, if possible, would seem to be the answer.
- Anonymous2 years ago
Looks like a problem with the fan limit switch. It could be failing or the blower wheel is dirty and not providing proper air volume.
- elhighLv 72 years ago
It sounds to me like the blower is pulling too much heat off the plenum, and it's cooling below the cutoff threshold. You need to increase the hot water flow rate through the plenum, lower that threshold setting, or reduce the mass of air per second moving through the plenum.
Adjusting the threshold setting is probably not possible, but the blower is a different story. It may be as simple as adjusting a damper on the blower to reduce its output. Similarly, increasing the flow rate through the plenum may be a matter of opening a control valve another turn or two.
You have all the controls right there in front of you, and we don't. If it isn't entirely clear or you aren't completely confident in your ability to experiment, you may feel better calling in an HVAC pro. How you proceed is up to you.
Good luck with it.
