HVAC Question

Brent

Member
My wife and I recently "completed" a major renovation and during the process I had to reroute some HVAC. We currently have a vent that leads into our attached garage, but it has been sealed off to avoid wasting heat in an unnecessary space. We have the same situation going on in the laundry room that we have decided doesn't need to be heated as it was simply built into an area of the garage. The duct work to both vents is side by side at the end of a long run furthest away from the furnace. Would I benefit from removing this extra unnecessary duct work and capping them off where the come off of the main trunk? Would it have adverse effects to the system?


Sent from my iPad using Deer Hunter Forum
 
Here is what I would do. Get a large piece of cardboard and a roll of duct tape. Close the end of the trunk line at the point of use (the vents) in the areas you don't want to heat. Let the furnace run a few times and see what the air flow in the rest of the house is like.....check all the rooms. Listen for any flow noise and time how long the furnace runs. Do this a couple of times. Then close off the entire trunk line and see how that impacts your system.

I suspect you will see an increase in the outlet velocity of the heated air in the other rooms.....some may be more dramatic than others. Will it be enough to be an issue - I don't know. The thing is your furnace is going to produce the same amount of air at the same rate regardless if you have that trunk line open or not. By blocking it at the vents it still functions to some degree as far as the balance of the air flow thru the house. By closing it off at the source, now all that air has to go thru the remaining system. The same volume thru a smaller area increases the velocity. Sizes of these lines and how they are set up and the like can all play a factor.

Your best bet is a small trial and see how it actually affects the house. It isn't going to hurt the furnace, but you may find a curtain flailing in the new velocity or even a whistle being created somewhere that is not desirable, or even just an over all increase in the sound level of the air coming out of the vents. I understand your wanting to use the heated air as effectively as possible by possibly not heating that one trunk line. More than likely you will be fine, but it's always worth a look for piece of mind.

I am not an HVAC professional - my descriptions above are from my previous work in dust collection systems and how we used to have to balance and size collection lines to get the desired results. It was "sucking" this is "blowing" same concept just in reverse. I had sensors, probes, velocity meters and computer models at my disposal - you won't. I don't see it causing an issue, but a little trial will help you sleep better at night or determine if you need to bring a professional in to help adjust the balance & distribution with your recent changes.
 
Here is what I would do. Get a large piece of cardboard and a roll of duct tape. Close the end of the trunk line at the point of use (the vents) in the areas you don't want to heat. Let the furnace run a few times and see what the air flow in the rest of the house is like.....check all the rooms. Listen for any flow noise and time how long the furnace runs. Do this a couple of times. Then close off the entire trunk line and see how that impacts your system.

I suspect you will see an increase in the outlet velocity of the heated air in the other rooms.....some may be more dramatic than others. Will it be enough to be an issue - I don't know. The thing is your furnace is going to produce the same amount of air at the same rate regardless if you have that trunk line open or not. By blocking it at the vents it still functions to some degree as far as the balance of the air flow thru the house. By closing it off at the source, now all that air has to go thru the remaining system. The same volume thru a smaller area increases the velocity. Sizes of these lines and how they are set up and the like can all play a factor.

Your best bet is a small trial and see how it actually affects the house. It isn't going to hurt the furnace, but you may find a curtain flailing in the new velocity or even a whistle being created somewhere that is not desirable, or even just an over all increase in the sound level of the air coming out of the vents. I understand your wanting to use the heated air as effectively as possible by possibly not heating that one trunk line. More than likely you will be fine, but it's always worth a look for piece of mind.

I am not an HVAC professional - my descriptions above are from my previous work in dust collection systems and how we used to have to balance and size collection lines to get the desired results. It was "sucking" this is "blowing" same concept just in reverse. I had sensors, probes, velocity meters and computer models at my disposal - you won't. I don't see it causing an issue, but a little trial will help you sleep better at night or determine if you need to bring a professional in to help adjust the balance & distribution with your recent changes.

Thanks J-Bird! This is the kind of input I was looking for. I already have both vents blocked off, but I haven't tried blocking them at the trunk just yet. Might give that a try tonight and see how things go. Thank you for taking the time to respond!
 
Mine have shut offs at the main trunk line, so you may not have to do the cardboard deal. Chance of freeze of pipes in the laundry area without heat?
 
Air is a fluid like water is. If air can't go out the outlet, can any go into the inlet? Might not make a difference on where you shut it off...

Also, I've read that plugging vents can cause more pressure at the fan causing it to work harder. Kind of like trying to blow honey through a straw vs water. Is there any way you can meter power consumption through your system and compare open vents with closed vents? Not trying to tell you one way or the other is best, but like j-bird said you might do some small (easy) changes and look for issues before digging too far into it.
 
Mine have shut offs at the main trunk line, so you may not have to do the cardboard deal. Chance of freeze of pipes in the laundry area without heat?
I don't think ours have any shutoffs on the trunk, but I'll be sure to check. That would be much easier!

I thought about the possibility of washer hoses freezing, but our garage and garage door are insulated and the laundry room is a small room within the garage. It gets chilly in there, but never cold enough to freeze. I did buy the pvc wrapped stainless steal hoses just to be safe.
 
Air is a fluid like water is. If air can't go out the outlet, can any go into the inlet? Might not make a difference on where you shut it off...

Also, I've read that plugging vents can cause more pressure at the fan causing it to work harder. Kind of like trying to blow honey through a straw vs water. Is there any way you can meter power consumption through your system and compare open vents with closed vents? Not trying to tell you one way or the other is best, but like j-bird said you might do some small (easy) changes and look for issues before digging too far into it.

I wondered how it would affect the fan and overall pressure throughout the system.. I've been reading into the subject a bit since posting and it seems that the increase in pressure can cause a lot of problems within the system and actually cause increased energy usage. It sounds like I'm going to be better off allowing normal airflow throughout the system as it was designed. Less stress on the furnace, proper air pressure and circulation maintained, and an evenly heated house.
 
Last edited:
I don't think you will notice any difference but if you do decide to cut them off the main trunk, make sure you leave the main trunk line past the last split as the trunk needs pressure to evenly distribute to all vents.
 
I don't think you will notice any difference but if you do decide to cut them off the main trunk, make sure you leave the main trunk line past the last split as the trunk needs pressure to evenly distribute to all vents.

Yeah, I'm going to avoid blocking off any vents and just going to let the system operate as it was designed to do. Seems that I was being mislead by an old myth that shutting off vents would help save on energy costs. From what I've read, it seems that it actually does the complete opposite.
 
Last edited:
Back
Top