Combustion air/ free air...

heatpro02920

Hey fellas, I am looking for some insight on a specific topic.

What is your method of figuring free space, I have a job we were called in to repair {remodel}, has 2- 80K BTU 90+ furnaces and an 80 ga 75K BTU direct vent water heater all in the basement using free air for combustion. My proposal was to pipe in outside combustion air to all 3 units and the banks inspector said there is plenty of free space for the 3 appliances...

So what math do you guys use?

Ross_24

I use 50 cu ft per 1000 BTUs to find if I need make up air. I believe that's what the Massachusetts code calls for unless I have my numbers mixed up. I typically refer to the NFPA 54 for make up air options.

Keep in mind if the basement is loaded with storage items those take up air space so you will need to subtract that.

EBEBRATT-Ed

LOL Excellent point ROSS I have never been in a Banks mechanical room that wasn't all cluttered up.

Heatpro, The DV water heater does that not have a pipe through the sidewall flue out and air in concentric vent? If so you don't need to count the WH.

Tell the bank you will get better efficiency using Outside air you won't be loosing building heat up the flue.

jonny88

Field control make an excellent product (fan in a can) brings in outside air when units fire.Havent figured how to attach link.Welcome back by the way.

Rich_49

I wonder if they realize that that free air gets drawn in through the cracks and raises the heat load ? Is the building even leaky enough to provide that free air ? Code is the only math we can use in this situation . Maybe the bank's inspector will sign a hold harmless agreement . Without knowing exactly how leaky the building is I would cite the manufacturers recommendation that all combustion air be brought in from outside and discard the free air allowance of drawing from inside .
If the building is of unusually tight construction air shall be obtained from outdoors in accordance with sections 703,705,706 or 707 of IMC .

Section 707 .
Fuel burning appliances that are listed and labeled for direct combustion air connection to the outdoors SHALL be installed in accordance with the manufacturer's installation instructions .
Just because the manufacturer may recognize that you can use indoor free air does not limit your exposure to future litigation .

Don't know where you are located but most of these types codes vary very little .

1 CFM per 2,400 Btu/h minimum or in your case 100CFM x 60 minutes = 6000 CFH . Just to be clear that is approximately a 750 sq ft building worth of air every hour .

heatpro02920

I guess there is enough air on paper since there is 21000 cf. I dont know, the bank doesnt want to do it, obviously..

Jack

In a past life I was the Tjernlund rep. I cannot tell you how many places I'd get called to that had plenty of "free space". Yes, it WAS free space, but the minute the inspections were done the homeowner was dragging a pile of 2x4's down the bulkhead and building a wall 6" off the side of the appliances. You can see them now. " that should be enough space for THEM!" As well, I've seen so many basements with 6' of stuff. Then people will argue with you that the outside dimensions of the structure are all that matter. Yes, and its current condition proves it. It is not accident that the two manuf of power venters are also the manuf of mechanical combustion air systems. Outside combustion air...always!

jonny88

welcome back Jack and as always you make sense in a few sentences.

j a_2

Jack, I definitely, agree with you about , the fact Mr handyman/homeowner, even Mr. Carpenter company…so often remodels there basement/boiler room without any consideration given to the fact that there is a fuel burning appliance down there…Unlike humans, if we can’t breath we die, if the appliance can’t breathe it kills people…..and it keeps on living, looking for more victims being stupid…Its really a good day for the lucky homeowners who happen upon this site, and realize there is just a tiny tiny bit more to all this, than just screwing a bunch nipples together and soldering a copper pipe...

BobC

A friend of mine converted his cellar to a office and playroom (all well insulated) and he enclosed the boiler and HWH in a 8 ft sq room. I told him to put a louver into the bottom half of the window to get combustion air into the appliances. He also has a CO alarm in that room

When he had his 30 yr old furnace replaced last year the installer told him how many houses he had been in where no provision had been made for combustion air. He then had to convince the homeowner to spend the money to put in a fan in a can. I can just imagine the wailing and gnashing of teeth.

Bob

j a_2

Thats great…Pretty much all appliance manufactures have 6-8 pages of warnings and cautions preceding the piping diagram..They even put it in big print…It is also in our code that the install manual be placed on or near the appliance,and left there…Make up air is so often overlooked…An opening in any window to the outside would be my very last option...

rick in Alaska

Just looked at a house yesterday that had a gas conversion done. The guy put in a Burnham esc rated at 170,000 btu for a 1600 foot, decently insulated house. So he can have enough capacity to make the hot water in the indirect you know........
Luckily the state caught up to him before he installed too many like this, but not quick enough. A few out there like this.
Anyway, I was there to look at another problem and noticed the combustion air for this room was a 5" pipe going through the wall, belled down to a 4" ,and then with a screened, louvered vent cover. My guess would be about 2" total free area. Have to go back Monday when parts get in, but for now we have a full eight inch hole through the wall and some crawl space ventilation.
I just wish the homeowner could sue the guy to get the heating system taken out and a right sized unit put in, but not going to happen. He burned a lot of people.
Rick

Jack

j a said:

Thats great…Pretty much all appliance manufactures have 6-8 pages of warnings and cautions preceding the piping diagram..They even put it in big print…It is also in our code that the install manual be placed on or near the appliance,and left there…Make up air is so often overlooked…An opening in any window to the outside would be my very last option...

In 54 and Manuf Instructions they show all the acceptable methods of providing outside air. Over the years In all my system inspections I would refer to the one that showed the duct going to the floor with a 180* return bend. One thing about that method is that I solved one of every families mysteries. The mystery of the missing socks. They are all in that duct! All that cold air spilling in.....

j a_2

rick in Alaska said:

Just looked at a house yesterday that had a gas conversion done. The guy put in a Burnham esc rated at 170,000 btu for a 1600 foot, decently insulated house. So he can have enough capacity to make the hot water in the indirect you know........
Luckily the state caught up to him before he installed too many like this, but not quick enough. A few out there like this.
Anyway, I was there to look at another problem and noticed the combustion air for this room was a 5" pipe going through the wall, belled down to a 4" ,and then with a screened, louvered vent cover. My guess would be about 2" total free area. Have to go back Monday when parts get in, but for now we have a full eight inch hole through the wall and some crawl space ventilation.
I just wish the homeowner could sue the guy to get the heating system taken out and a right sized unit put in, but not going to happen. He burned a lot of people.
Rick

What pray tell was he thinking ?