Moving Furnace - Slab & Crawl Space questions

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LeBlanc

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After viewing these postings for a while and after giving lots of thought to my options, I have decided to replace my natural gas hot water heat system with a natural gas forced air heat system. Several questions are still an issue and I'm seeking guidance.

My preference is to do all of the grunt work to save money. I am a mechanically-inclined novice when it comes to HVAC and will purchase professional help for necessary portions of this project.

The attached graphic shows the footprint of our 1400 square foot Mid-Michigan cottage. The lower portion (approximately 400 sf) is on a slab (as outlined by the thick red border line) and the upper half (approximately 1000 sf) represents the portion of the house on a somewhat tight crawl space.

The heating system and water service items are currently located on a slab in the area marked by the large X (in a part of the large garage that is being converted to living space). As part of a larger renovation, my plan is to move everything to the adjacent area (also on a slab, about 12 feet from their current location) that is salmon colored on the graphic.

Question 1 - Calculations from several sources indicate we should select a furnace of about 77,000 BTU's. Does this sound right for 1400 sf in Mid-Michigan?

Q 2 - Should the new furnace be an updraft or downdraft? I can purchase either type of furnace from a wholesaler and since the majority of the house will be ducted through the crawl space, it seems the downdraft makes more sense.

Q 3 - My preference is to run heat duct in the crawl space to all crawl space rooms, and I'll probably need to duct the rooms on the slab through the attic. Is this allowable and advisable? Is it realistic?

Q 4 - The new 93% furnace will be about 12 feet diagonally away from the existing vent / chimney. Can I attach to the existing vent or should I construct a new vent straight upward from where the furnace is placed?

Q 5 - Since the new furnace will be in the house, and since the room holding the water service items and the furnace will be essentially a large closet (about 4' x 8') what can I do to ensure adequate fresh air? Will louvered closet doors suffice?

I will probably have more questions later. Thank you for providing feedback.

Richard
 

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Jimbo

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1) If the furnace is on the main floor with ductwork mostly below, then down draft makes sense.
2) This is not a number you can pick out of the air. You are adding living space. You need someone to do a formal Manal J calculation heat loss calculation. Too small or too big...both are bad. http://www.acca.org/

4) Very unlikely. Venting 90+ furnaces is a different animal. You need to follow very closely the detailed installation and venting requirements found in the manufacturer's installation instruction, and also comply with all requirements of the National Fuel Gas Code: http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=54&cookie_test=1

5) You are headed for trouble here. There are very specific combustion air requirements for gas burning appliances, found in the same places as paragraph (4) above. If you screw this up, it can be life-threating dangerous, as well as causing problematic operation of the equipment.

In addition, in many places now, for energy purposes, the building codes may require outside combustion air, and/or a fresh air mix for the heated air due to "tight house" syndrome.

Are you aware that almost any jurisdiction in the country will require one or more permits for this job?? Many area do in fact allow homeowners to do even this scope of work, but the permits and inspections are mandatory.


If you can tell us the brand and model of furnace you are looking at , we may have access on line to manuals, to get a better idea of what you are getting in to.


We will always help out do-it-yourselfers here. That is why there is a forum. But you will also hear some advice in the negative when jobs of this scope are proposed. Hang in there!
 
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