We have a 110 year old Victorian in NJ with a single zone forced air heat with central AC. There is very low air-flow through the 2nd floor air vents. I need some advice on diagnosing and potentially fixing this problem.
The furnace was just replaced with an ultra-high efficiency variable fan speed unit and the central AC compressor is new and appropriately sized. There is a single zone controlled by a 1st floor thermostat. The visible ducting in the basement is probably 20 years old, and is well-installed and taped. Some of the connections to the original ducts (of which some are in the exterior walls) were poorly connected, but we’ve fixed those connections.
This is not too much of a problem in the winter as the heat rises. In the summer there are pronounced temperature differences – the basement is really cold, the 1st floor OK, and the 2nd floor too hot.
The HVAC folks that were out to install the furnace said there was no technology to diagnose or fix the problem. They thought I should remodel the 3rd floor and add a separate heating/AC system to the 3rd floor with some penetrations to the ceiling of the 2nd floor. This may help the 2nd floor but won’t fix the air layering, and seems wasteful. Are they really correct that this problem is very difficult to fix?
Replies
More that likely you are loosing a lot of supply air out of the runs to the upper floors. Go to http://www.aeroseal.com I used them in my house. Made a big difference on upper floors.
Can we assume the furnace/AC is in the basement feeding up two floors?
Do you have balancing dampers in the system (I had a really old system in an old house and surprisingly every main branch had a damper in it ... I was lucky).
Dampers serving ducts to basement/first floor would allow you to force more air to 2nd floor in summer and open them for winter. Dampers are simple. Retrofitting them may or may not be a hassle. Just a thought.
Getting advice from many contractors ... they often don't want to put out much effort or be very creative (many CAN'T be very creative). No offense to the good contractors out there! They may tend to offer the easiest and/or most profitable solution for them.
are there any returns in the upper floors?
You can pump all of the coldd air up that you want to, but without any returns the cold air will go donw the stairs and the hot air will sit at the top of the upper floors.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
You need to have the distribution system balanced fo air floow. It may possible to add dampers the existing ducts to achieve the needed supply air for the load requirements of the second floor. Sometimes that may not be enough.
Older homes were usually "heat only" distribution systems, and as you noted work fairly well. Later as a/c became more common, someone "upgraded" the system but utilized the old duct work. Simply put, the distribution and return duct were system were not designed for cooling. Furnaces and air conditioning systems have evolved over the years. They are much better than they were 30 years ago, but that doesn't mean they are good enough to overcome a basic design short fall.
Have another contractor (or your lastest one) do the load calculations for each floor, room and area of the house. This will tell you how many BTU/hr of heating and air conditioning each room/area must have to maintain the design temperature. If the new equipment meets the total design loads you are only halfway there. It must also supply the correct number of cfm of conditioned air to each room/area to satisfy its' load requirement.
It may be that you need to upgrade the distribution system to the whole house. If you find the contractor that will run the load calculations for you, and show them to you, you will find the guy that is most likely to solve you problem correctly. They will also check the cfm deleivered to each supply vent to see that it is correct if they do have to install a new system for you.
Most of the really good contractors that do that sort of work you field measurements of the existing home and the run a computer model that helps with the design.
Be leery of the guys that say they can fix the problem by just adding more and more capacity, that you may not need. Energy is to costly these days to mess with "back of the napkin" calculations or the guys that say "we've always fixed it that way."