Garage heater horizontal vent slope

Hi everyone,

Regarding the vent slope for a hot dawg/ big maxx forced air heater... Manual states upslope 1/4" per foot. This means condensate will run toward the heater, seems backwards to me. Can someone explain this upslope requirment.

Seems like a power vent would not care about the upslope.

Thanks.

Assuming you are using B-vent on the flue, which you should do, you should not have condensate. That said, under the right conditions every system can condense. Proper flue design will ensure that you limit this period of condensate (its called the wet-time) to short periods. Installing with a 1/4"/ft rise will ensure that residual hot/warm flue gases will exit on their own. Does your HD have an adjustable post purge on it?

segermech said:

Hi everyone,

Regarding the vent slope for a hot dawg/ big maxx forced air heater... Manual states upslope 1/4" per foot. This means condensate will run toward the heater, seems backwards to me. Can someone explain this upslope requirment.

Seems like a power vent would not care about the upslope.

Thanks.

Click to expand...

This is for my Dayton unit heater, a 150K (propane) unit:

Dayton Operating Instructions and Parts Manual said:

The vent air system must be installed to prevent collection of condensate. Pitch horizontal pipes downward 1/4 inch per foot (21 mm per meter) toward the outlet for condensate drainage.

Click to expand...

This is a copy and paste from the manual. BTW, it is a power vented, Category III appliance.

That said (and quoted) the ONLY authority is the manufacturer's requirements, if they say slope up, then that is what is required. So yes, your intuition is basically correct, but not for all heaters.

Not familiar with your particular heater, but every other heater manual I've looked at requires either a DOWNslope in the vent pipe or an upslope with a condensate drain near the heater.

I installed my Mr. Heater 45k unit with about 1/4" down drop over the 4 foot B vent exhaust. Seems to work just fine.

The Mr.Heater FHA hanging heaters utilizing a horizontal vent system and installed per code as well as the Manuf. installation instruction, requires it to be installed with a 1/4" rise per foot for a residential installation. As "Jackfre" mentioned in post # 2 he is correct. In addition, whatever condensate does exist for the short wet-time period, it is burned off because of the high flue temperatures.

With the change in catagory classifications and the use of b-vent and not single wall, one of the concerns was that when using single wall vent, uninsulated and installed in non-conditioned space, single wall would condense much quicker.

Many people also think that if being installed in a "detached" garage it is considered commercial (non-living space). It's typically determined by the towns zoning if considered residential or commercial regardless of how may if any detached buildings you have.

Min 1/4" per foot upslope.

The heater is designed to handle the condensate. What do you think happens with a vertical vent?

If you are worried about condensate draining, put a T fitting on the vent outlet of the heater. The new Mr. Heater manual actualy shows this as being a requirement for commercial installations.