Shop House HVAC air intake question?

[mattshup]

I currently live in a shop house style setup. Shop (3400 sq. ft.) was built in 1973 with living quarters (848 sq. ft.) added between 2010-2017. (Long process). The shop has a 200,000 BTU propane Modine heater in it which works fine. On top of the living quarters, still inside the shop but enclosed in a small room is the High Efficiency Guardian HVAC system and hot water heater. When I had the furnace installed, the hvac guys put air returns in 3 rooms of the living quarters and left the fresh air intake open so it just ***** air in from inside the shop. Problem is when working (painting, gas, exhaust fumes) the HVAC system will **** in that smell and bring it into the living quarters. My HVAC guys said it won't matter because with it being a "high efficiency" furnace the fresh air intake is only for the combustion chamber which is sealed separately from the air that circulates around the house.

Is my HVAC guy wrong? Should I put a pipe to the outside wall for ACTUAL fresh air rather than drawing from inside the shop. My first instinct is to obviously do that but my HVAC guy is adamant that the fresh air intake is strictly for combustion and won't effect the smell difference in the living quarters.

I am sure I left some crucial detail entirely out of the picture but if anyone has any suggestions or opinions I would really appreciate it! Can always provide more info as needed also!

 

[PoorUB]

If you are asking about the 2" or 3" PVC used for combustion air it can cause a negative in the space when the burner is running.
I would run the combustion air to the outside and also consider running a 4" vent from the outside to the return air. It will help pressurize the living area when the blower is running. Another option would be to add an air exchanger drawing air from the shop and dump the fresh air into the living area.

 

[Jim greengo]

I wouldnt want flammable vapors from a shop getting sucked in to a furnace for combustion air,sounds like a good way to get blown off of the map to me.

 

[nadogail]

If you are getting shop smells in your living space, something is not right.

 

[PoorUB]

I wouldnt want flammable vapors from a shop getting sucked in to a furnace for combustion air,sounds like a good way to get blown off of the map to me.

Jim. His Modine shop heater is doing the same thing!

 

[Steve in UT]

Seal and insulate the furnace room from both house and shop. Vent the room to the outside. Both furnace and water heater should be fine drawing combustion air from the room if it is vented. If you are getting smells from the furnace it is because your return air is not sealed good and it is sucking shop air. Smells are hard to keep from wafting from garages to houses. As mentioned above, a small amount of outside air pulled into the return line might help pressurize the living space and keep shop air out.

 

[fitter30]

Have to pressurized the living space with outside air by either adding a vent to your furnace, cracking a window or energy recovery ventilator

 

[Jackfre]

What is the input on the furnace in the residence? Is it a condensing furnace? How far from an outside wall is the furnace? Your contractor is correct that it will run as he has installed it, but he was just lazy in the install, not bothering to do the correct job and that is to isolate both systems. The way to do that is to provide adequate CA to the residential furnace.

 

[LS6 Tommy]

Combustion air should come from a "clean" source, but any odors being sucked into the combustion intake shouldn't be noticable in the conditioned space. Something is very wrong.

Tommy