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Little back story - A while ago, I had a contractor out and in passing complained about how cold my house is in the winter (brick, no real insulation) -- brilliantly, he says "well, yea, your furnace is in the front of the house, and it’s what? 60 feet at least to that addition? No wonder you're not getting any heat back there" ... I'll be damned what a great idea.

Earlier this week, I finally had my furnace moved to a far more central location in the house ... actually it's as centered as humanly possible without being in the middle of a walk way. The vents in the middle of the house, of course blasts air, the rear of the house a little more but the front ... not NEARLY as much, you can barely feel it -- this concerned me quite a bit (I was wondering if I had made a mistake). Anyway, last night I turned it on for the first time "let’s see how this baby works" -- it went from 64' to 70 in under 45 minutes (!!!!! <-- me excited). What really confused me is the front of the house was just as warm as the rest. This defies logic.

Maybe there's no real answer, but I'm really curious how this works and if I should worry about improving the ducting to the front so the flow is more balanced or just leave it alone?

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Not an HVAC guy, but it seems like since hot air is going to expand, the vents in the middle are probably supplying the air you're feeling in the front. Alternatively, if there are more branches to the front of the house, you'd have reduced air flow at each vent, but still an aggregated amount of heat. –  Steve Jackson Oct 6 '10 at 19:28
    
Where is your thermostat -- near the center of the house or closer to the perimeter? –  Mike Powell Oct 7 '10 at 2:03
    
its in a central location (1st floor, opposite the new furnace loaction and near stairs going to the basement) and is generally "more correct" than the rest of the house. –  jeriley Oct 11 '10 at 19:15
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2 Answers 2

up vote 5 down vote accepted

If it works to your satisfaction (that is, if it heats the house properly), then leave it alone. There are a LOT of factors in this, including: length of individual duct runs openings between rooms (door or no door, closed or open if door) sizes of rooms placement of vents in the rooms placement of the return vents

I'm no HVAC guy, but I know enough to know that if it's working, DON'T mess with it further.

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In a large building there is a process that takes place during construction called air balancing where the airflow from each supply and return is measured and adjusted against a spec. Basically you use this big flow hood device and measure the CFM of air through your registers.

Air flow to each space is calculated by a mechanical consulting engineer who takes a bunch of factors into consideration regarding the heating, cooling and make up and air change requirements for a particluar space. It's never done in a residential property unless you're talking about a big baller mansion using a commercial HVAC system.

Anyhow - the issues you described with the rooms located on long duct runs away from the furnace is a common problem. Moving your furnace was a smart idea considering you really have no other control over how much air is delivered to each room. A residential HVAC control scheme is vastly different because the airflow and heat is on demand - and you have zero control over the volume of air delivered.

If you really want to try and tweak the airflow towards your more distant rooms, the only thing you can really do is to block off part of the discharge register(s) closest to the furnace - that will help push air to the most distant parts of the ductwork, at the expense of not delivering as much heating to the other spaces. Also, insulating your ductwork and ensuring all the joints are sealed (taped) will help a ton.

All this aside - I don't miss working in the HVAC world one bit.

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I'd heard of this (measuring the cfm). And I have done exactly that, blocking of the big one in the middle room on the 2nd floor -- causes a nice floating effect on a small area rug (hehe). Really need to clean up that register so it opens/closes easily. I've sealed up most of it with that ungodly expensive foil tape so that shouldn't be an issue :-) –  jeriley Oct 11 '10 at 19:19
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