Variable speed blower better or worse for temp differences between floors?
I have a townhouse with a 20-year-old 2-ton heat pump I'm getting estimates to have replaced. The main issue I'm looking to address is the noticeable temperature difference in the summer between the main floor and the warmer upstairs. So far I've mostly been told that a variable-speed blower would help this, and upgrading to a 2.5-ton unit would be less efficient.
However, I've now heard one counter argument: with a variable-speed blower, the main floor's thermostat would reach the desired temperature with a lower fan speed, and the system would shut off, with the upstairs having received less airflow and thus creating an even greater temperature difference. This contractor advised a single-speed air handler with a 2.5-ton unit to increase upstairs airflow.
So my question is, what would be best to keep temperatures even throughout the house? A variable-speed blower running either on auto or continuously, or a larger unit with a single-speed blower?
V.S. in the "on" position if it is set up properly. In that setting it should ramp up to 40% and mix the air well without the cold air blowing feeling in the heat mode.
The cooling capacity delivered ot each floor will be proportionaly wth airflow. With lower airlfow it might distribute it more evenly since some dynamic air resistance will be reduced. Also, with lower airflwo, you mgith be able ot add manaul dampers and better balance the system. 2 story buildings almost always need either manaual or autoamtic zone dampers or 2 systems.
Does your current 2 ton keep up in summer otherwise? Does it run almost continously in the hottest weather for 4-5 hours ro more? Have you made and effciency imrpovements?
Going to a 1.5 Ton if a load calculaiton supprots it, or going with a 2 stage 2 ton unit may help your temperature imbalance.
No efficiency improvements. The current unit does a good job of keeping it cool in the summer, and it doesn't run constantly, though I keep it at a pretty conservative temperature since it's older. Load calculation shows that a 1.5 ton unit would be just a bit too small.
Originally Posted by motoguy128
SOmetimes just a bit too small is better than a little big. Manual J has some "fudge factor" built-in. Longer run times will improve temrpature distribution and lwoer airflows will allow you to reduce airflwo to the areas that are over conditioned (downstairs) thereby forcing more air ot the areas under conditioned (upstairs).
Another way to improve airflwo upstairs is to install better quality supply registers. The standard cheap stamped steel units are far more restrictive than better quality commerical grills. Sometimes that small change alone cna increase airflwo enough to solve the problem. In winter, if it gets too warm, the upstairs registers could easily be pinched back a little.
You still might consider a 2 stage 2 ton unit either way.
Most contractor know just enough to say that a VP blower will "make a difference." However, they do not mention the real problems that would really solve the problem.
Originally Posted by willdude
The reason for this is two fold. One is that they are too lazy to look into the real problem (it's is much easier to say the blower will solve all the issues). The other reson is that most are too ignorant to know how to fix the airflow problem.
There is no excuse that a 2-story home has a hotter 2nd floor. But, if you talk to most contractors, what do they tell you? Most will say, "That is just the way it is with a 2 story home." If you hear this, thank them for their time, and send them on to the next sucker.
Cant find a delete button. Just realized I violated the AOP posting rules.
Last edited by Precise; 11-29-2012 at 03:34 PM.
Reason: Violation of the AOP posting rules.