I need to vent my 9' x 3' (with 8' ceiling) furnace room that contains my furnace 92,000 btu and tankless water heater 199,000 btu

The tankless Water Heater can be installed with the ability to take in combustion air from the outside via a 3 inch intake vent. If needed.

I don't want to place a vent in the top and bottom of the door, as I may later enclose this area for a sunroom. This is a single story home but I have a vented crawl space, Can I place a hole in floor cover with a grate or should I duct it to the outside?

How can I get this upper vent requirement without cutting a hole in outside door or outside wall? I have a vented attic. Can I just vent into the attic? Would I have a code problem as if a fire started in this small room it could just access the attic. Would I have to duct to and through the roof.

Thanks

First check with your local building department.

You seem to be aware of the requirement for 50% of the required square inch opening for combustion air high and 50% of the required square inch for combustion air low

In this area you can take both your high and low out of the attic.
Note: Some areas of the country look at the code differently

You cut a hole at ceiling level and extend a round metal duct of the necessary size down about 12 inches this takes care of the high combustion air requirements.

Next cut a hole at ceiling level ceiling but this time run the pipe all the way down to about 12 inches from the floor.

This will give you both high and low out of the attic and meets code here.

Now you will have to make sure there is enough attic venting to allow you to use this system and make sure the holes you cut in the drywall are accurate. You do not want to leave any open areas around the pipes penetrating the ceiling.

Many times on inspections we find rags stuffed into the pipes because the home owner says cold air is comming out there and they blocked them to save energy. LOL

One more thought. While you are spending some $$$$ see what a new style furnace would cost you. This way both of your appliances will draw combustion air from the outside thru PVC pipe and your venting problem will be solved. It will also make your heating bills a lot cheaper.

Check out powered device called a "Fan-in-a-Can". You can get by with only one opening and it will not allow cold air in without a call for heat or hot water.

hvac1000

"County Inspector"

Yes, Once I have a plan on what to do I will contact County inspector prior to doing the actual work.

"Aware of the requirement for 50%"

Please I do not understand do you mean, Do I need twice the ventilation area? If I combine the two units btu’s it would equal 291,000 btu’s divided by 2000 which would require 145.5 sq inches

"Furnace upgrade"
I have considered up grading my furnace what would you recommend? One of the problems I have with my mechanical room is it is to small Though county plan review passed the blue prints and framing inspectors all passed construction. After dry walling another inspector said I needed 3’ in front of heater for code (so it could be worked on) That’s why I plan to install a tankless instead of a regular water heater to give me more room. If I could replace the never used older heater with a better unit which was smaller I might just do it.

"How to Calc for Attic venting"
What calc’s do I need to figure if I have enough attic venting

You need to have a set amount of ventilation based upon the BTU requirements of the unit (s) requiring combustion air. You do not need twice the ventilation you need to split the ventilation required by 2. The you take 1/2 of it from high location and the other 1/2 from low location.

At 145 sq inches of free area (deduct for any grill used usually 25%) it will be one cold area. LOL

First you need to see how much attic ventilation you have. Measure and count the number of low vents and the number of high vents in the attic space. The calculate the free air amount.

This will determine weather or not you have enough attic vent to start with.
Next step when armed with this information is to call the building dept and ask the if what you have is acceptable to code or if you need to add more vents to the attic space.

I say call the building dept because no matter what you figure if it is going to be approved and inspected by a inspector. If you get the figures from the inspector and approval for what you are doing on the phone it makes it just about impossible to turn you down on the job site.

LooK at your furnace install instructions. you might find that the manufacture only requires 24 to 30 inches. In this area the manufactures instructions over ride the local building code. This might save you a few inches.

One thing I could never figure out as a contractor (small 37 man corporation),inspector (multiple state certified) or a teacher of code classes accepted for recert credit for contractors in (three states at a local university), why do people want to CRAM all the goodies in to a such small locations. 3x9 sound big until you load all the toys into it.

The tip I gave you about the building department always works in our area of the country. Actually knowledgeable inspectors like to have questions asked first so when they get to the job site for a inspection they do not have to write the dreaded (red tag) for a failure to comply to code.

One other note always leave the instillation papers on site in the location of the equipment. This will allow the inspector to review the manufactures instructions as to how the equipment is supposed to be installed.

As we are all aware different area have different codes and some citys actually write there own codes. For vent/combustion air requirements refer to there judgement or the manufacturers instructions for size of openings and actual number of sq inches free air required.

Good luck with your project.

Thanks for your tips,
To answer your question of “why do people want to CRAM all the goodies in to a such small locations. 3x9 sound big until you load all the toys into it”

In my case the architect drew up this design and the county didn’t catch that this room was to small, So much for relying on county inspectors. I have spoken to the county about ventilation and I do not get any ideas except for “Oh just install a couple of vents in the top and bottom of door.”


#1, OK, I will start again, I can count lower and high vents in my attic. I would assume I need to know the sq inch total of lower vents and the sq inch total of the higher vents. If I don’t have enough vent area in my attic then it is a waste of time for me to plan to vent my mechanical room in to the attic. Please what is the formula that I need to figure if my attic area will work. I can increase the lower and upper vents if need be.


#2, Do I need to provide a vent in the floor to prevent any build up of propane gas if there were ever a gas leak?


#3, If I have 200,000 BTU‘s (furnace & tankless htr) by dividing it by 2000 would equal 100 which would mean I need to have 100 sq inches of combustion air 50 sq inches from low location and 50 sq inches from the high location

Is this correct?

((In my case the architect drew up this design and the county did not catch that this room was to small, So much for relying on county inspectors))

Now I see a little better what is going on with your job.

First I assume you paid the architect for his work ? If you did pay him he is responsible for the plans for your dwelling unit.

The architects plans did not really get a plan review by the county because all architects and engineers are exempt by the codes and have to stamp or sign the plans as proof of there accepting responsibility for the contents of the plans. This stamp/signature over rides all codes and requirements since as professionals they are accepting all responsibility for the plans and the safety of the home/dwelling unit. NOTE: This is the way it works in any jurisdiction I know of.

So the inspectors or the plan review people at the building department just look for the stamp or signature and automatically approve the plans.
The inspectors know this problem is between you and your architect and they are not going to get in the middle of it. Smart inspectors I say !!!

Your architect has a huge insurance policy for errors and omissions to cover his mistakes. My advice to you is that if you paid him for his services you need to go back to him with your problems and he should take care of the situation.

I am not going to allow myself to be put in the middle of your situation or problem and now I understand why as a new homeowner you were asking engineering questions.
Do the correct thing and get back with the architect who caused your problem to start with. It will be much easier on you in the long run since once you modify the architects plans of record you will be accepting responsibility for your entire project not him. This could create major problems in the future for you.

Good luck with your project.

A self help link is provided below.




Here is a link so read it and do your own calculations.
Then after you calculate the attic requirements add on the square inches you will need for your mechanical room requirements and add additional attic vents to the outside to compensate for the mechanical combustion air usage.

Roof Ventilation - Information about venting your roof space (http://www.roofhelp.com/ventilation_main.htm)

hvac1000
Why can't you just answer my questions. Instead of trying to read between the lines. I am not out to blame anyone, I just want to get a final on my house. Please don't over analize this. Please if you can't or won't answer my questions Please allow someone else to.

I am just trying to get the correct information

Thank you

((Please allow someone else to.))

Anyone that can see your post can answer your question.

If you read my last post back to you I gave you the answer. Just read the article as provided in Roof Ventilation. Just in case you missed it here it is again. Get a pencil and calculator and read the article for your answer. All the calculations formulas are contained in the article and the calculation formulas are what you asked for. Dang how much easier could I have made it for you. It also saved me much typing just to post the link to help you.

Here is a link so read it and do your own calculations.
Then after you calculate the attic requirements add on the square inches you will need for your mechanical room requirements and add additional attic vents to the outside to compensate for the mechanical combustion air usage.

Roof Ventilation - Information about venting your roof space (http://www.roofhelp.com/ventilation_main.htm)

Article primer.


A vent’s effectiveness is measured by its Net Free Vent Area. The Net Free Vent Area is the portion of the opening in the vent that actually ventilates. For instance, a vent can have an opening that measures 12 inches by 12 inches; this would appear as if it would yield 144 square inches of ventilation area. Because of louvers, an insect screen, or some other type of blockage, the actual ventilation area could be as little as 40 percent of that, yielding about 58 square inches of ventilation area. This 58 square inches is what’s known as the Net Free Vent Area, and is the amount that should be used when calculating how much venting you need.

Calculating how much venting your attic needs is relatively simple. All you need to know is the area of the attic floor. Include the garage, if you have one, and the soffited overhang because heat gets trapped above them, too. A common rule of thumb is the 1/300 rule, which means 1 square foot of net free vent area per 300 square feet of attic floor space. Let’s look at an example. Say you have an 1,800 square foot home with a garage that measures 20 feet by 22 feet. This will yield a total area of 2,240 square feet. You then divide this number by 300.

2,240 ÷300 @<hidden> 7.5
This tells us that we need 7.5 square feet of ventilation for the attic. Most attic vents are measured by square inches so we need to convert the 7.5 square feet to square inches. This is done by some simple multiplication. 1 square foot is equal to 144 square inches, so we multiply 7.5 by 144.
7.5 x 144 = 1,080
So we need 1,080 square inches of Net Free Vent Area. Divide this by two and we see that we need 540 square inches of intake ventilation and 540 square inches of exhaust ventilation.

There is always a lot of concern for what the best type of ventilation is. You have already read that you need both intake ventilation and exhaust ventilation installed at an approximate one to one (1:1) ratio. Now remember that the idea behind this is for maximum air circulation. Installing more than 1 square foot of ventilation per 300 square feet of attic floor space will not hurt anything – it’s a general guideline and code requirement in some areas. Most roofing professionals will agree that the best type of ventilation is continuous soffit and ridge ventilation. If a continuous exhaust vent and an equal or slightly greater amount of intake vent is installed, then the attic will be ventilated for its entire length

Thank you, I did go to and read the site you posted Roof Ventilation - Information about venting your roof space

I found this last reply informative, Thank you

You are welcome.

Now all you have to do is get it done.

Good Luck with your project.