Furnace in unfinished basement.
We have washer/dryer(vented outside), gas water heater, forced air gas furnace(combustion intake inside basement, exhaust outside) and water softner in our unfinihsed basement. There is no supply duct in basement. However, it feels quite warm in basement, almost as warm as house, even when there is 30 degree outside. So we are planning to insulate the basement ceiling. The question is, will insulating ceiling affect the furnace functioning? I am trying to find out why it feels so warm and cozy in basement when we don't need that at all! (we dont want to pay for it!) Is it because basement needs fresh air since combustion intake is insise? Could it be because of leaky supply/return ducts?
Thanks for your time.
I have a similar system in my basement. The furnace draws ambiant air from the basement and there are no supply vents in the basement, yet it isn't cold down there.
If your furnace is like mine, there is warm air being blown out the top of the heating unit. You can feel it when it's running.
If you have a relatively new house, the basement will be well insulated. I have a walk-out with windows and glass french doors and it still stays warm, even with the blinds blocking the sunlight.
However, I think you may have a problem if you finish the basement. You will probably end up isolating the furnace from the living space, thus eliminating what little heat is blowing out of the top of the furnace. In that case you will have to tap into the existing ducts with small diffusers to bring heat into the finished space. It's not a big deal, but it will reduce conditioned air pressure upstairs. That's why the basement vents must be either small or adjustable or both. Your furnace is sized for the first floor, not both floors.
If you end up walling off the furnace, make sure that all doors leading to the furnace have vent louvers so you don't starve the furnace of air or create a CO2 problem. A lack of supply air to the furnace and water heater will result in both of them drawing air DOWN the combustion stack, resulting in dangerous levels of CO2. Modern furnaces have an air sensor that will shut the unit off if the exhaust vent isn't drafting.
Man oh man!! You know, in fact I did find few gaps (each corner of a rectengular duct) at top of furnace (Janitrol 92.6% eff.) from where it is connected to the main supply duct. I thought I found a glitch where warm air was leaking out in quite a high velocity and guess what, I sealed it with a weatherstrip tape!!!! Basement was still warm and cozy.
However, I think your reply clearly answer my concern about isolating furnace who is sucking in air form basement. I'm just hit with a new gas bill which quite fascinating(and its just Novemeber!) and I am trying to lower it down.
Thanks for sharing your thoughts.
PS: What do I need to in order to get a reply from HK )
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