Again, I'm only posting this here because I genuinely love and trust my fellow pedes and know that we are a knowledgeable bunch!
My wife and I bought our first house a few months ago! It was built in 1912 and has beautiful american chestnut wood throughout. We love the home, I've been doing a lot of projects overall it hasnt needed anything major, just some stuff we want to change or update.
The furnace is an original gravity fed unit (aka octopus furnace) converted to natural gas complete with asbestos wrapped pipes lol. We were thinking of converting it to a forced air unit with the assistance of my uncle who is HVAC certified, but unfortunately he is going to have open heart surgery soon. I'm a new doctor working in a medical residency program, I have an ass ton of debt and a relatively small income for the time being so we don't want to shell out for a furnace right now if we dont have to. I'm a huge diy'er but I'll be honest my knowledge regarding HVAC is limited. We had a cold snap so we turned the furnace on today and it worked fantastically.
My question is regarding the exhaust vent, theres a damper on the exhaust vent that is open all the way, it comes off the main exhaust line perpendicularly. I just wasnt sure if that is supposed to be open all the way, closed or somewhere in the middle. I'd imagine the principle is that when it's open, the warm exhaust passing by creates a vacuum and sucks fresh air in to help push the exhaust up the chimney? But I'm really not sure lol. Any input is appreciated! Thanks everyone!
Pretty sure this is how your system introduces “make-up air.”
Without it, the exhaust would create negative pressure in the house and stress the motor from running freely.
I’d do a search on make-up air in relation to dampers. Despite the house being old and not as air tight as modern homes, it is an imperative part of proper air flow. You might find it allows cold air to return when the system is off. If the damper has a spring and is designed to close when the system isn’t running, make sure it’s free of rust and can close when air isn’t being drawn or forced by.
Hopefully this gives you a place to start in understanding your system.
This is a draft induction damper. It is just what you said, the warm exhaust passing by creates a vacuum and sucks fresh air in to help push the exhaust up the chimney, it is pulling air into the flue. Also, it helps when a strong wind that blows down the flue to not blow out your pilot.
Position should be partially to fully opened. Never closed. It is a proven, yet very old, method of inducing draft. It works and it is safe, but it is an energy hog since it is robbing your heated air from the house creating a negative. That negative is made up by drawing air from wherever it can. This is called "infiltration" and comes from cracks, leaky windows, doors, etc.
You do not want to rely on infiltration as a make-up air source. This is called drafts! Drafts can cause moisture and frost/icing problems.
Homes of this vintage were never "tight" they were very leaky and efficient. Nobody cared, oil and coal was cheap. Over the years as energy priced rose we tightened up our homes to save energy. New windows, siding, roofing, caulking and sealing, etc. (You stated your home is in very good condition so I assume this work has been done.
Going forward: If you plan on replacing the furnace this year or the next season, I recommend you keep the damper opened to the position it was in from the last owner. You can play with it if you want, but why fix something not broken.
DO THIS NOW: Get two CO detectors. They are relatively cheap. One for the basement and one placed nearest the bedroom/living areas. I am former PD and the majority of our calls in the coldest months were for CO related call.
Do this in the interim: If possible, connect a insulated flexible (easier) or rigid duct duct to the intake and pipe it to outside. This will allow 100% outside air to feed into the flue, hence it is not robbing your home of energy. You could split off and feed some fresh air to the burner section as well for combustion air.
I will draw a sketch as attach it shortly.
(Source: Me - 33 years professional HVAC engineer)
Thank you so much for the indepth explanation! I really appreciate it! I'm not 100% what work has been done in regards to sealing it up. I can tell you that the knob and tube was removed (mostly, still some in the walls running lights with two switches for the common wire) but upgraded with romex wiring, 200 amp breaker. All the water lines are pex except for the main which is still the old cast iron type (hoping that never blows lol). As far as I can tell there is blown in insulation, havent taken a wall off yet but given it was 30 last night and the house was 65 this am I'm willing to bet theres insulation. Windows are about 5 years old throughout. Roof is on its last leg lol has 2-3 layers already, top layer probably has a few years left, not leaking yet but can tell it's on it's way out. I plan on just taking off the top layers and shingling over.
Luckily the registers are actually positioned properly, the return airs are on exterior walls and the hot air vents are on interior walls. From what I understand, that's not usually the case with these old furnaces.
We have a CO detector on the second floor, I set it on the hot air vent while it was running and it was at 0 the whole time but good idea buying more. Should they be lower to the ground or higher? CO is lighter than air so I would assume it would accumulate higher up and more would be required before a detector placed close to the ground would register it?
And yes good idea about the damper, I wont mess with it but wanted to make sure that open was the proper operational position, and that the previous owners hadnt opened it for the summer or something when it should actually be closed.
For the asbestos wrapped pipes, assuming we dont change the furnace should I paint over the asbestos to lock it in? If so, what paint type would you recommend?
Thank you again so much for all your help! I will go through your post and check everything.
Outside Air Intake
Here is a simple sketch. Sorry it is so crude.
Battery CO detectors near top of door frame. 120v at floor receptacle.
Asbestos insulation that is torn, ripped or damaged should be painted so as to be encapsulated. Fiberlock ABC Asbestos Binding Compound is an example, but there are many other good products.
I love the sketch!!! Thank you so much for taking the time to draw that, makes 100% sense now! I will see about adding the line to the outside
Post a pic or sketch.
Posted above, good idea
Pics: https://i.ma.ga/DUsFm.jpg
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https://i.ma.ga/ebPDg.jpg