Retrofitting my small abode old HVAC System

[blackbriar51]

Hi Fellas,
Hoping someone can help me here with some good decisions.
Getting closer to 60 yrs. I believe i will probably winter it out here until the end but one never knows.
I am slowly remodeling and moving different house features around to make life more comfortable and more roomy inclusive to upgrading technology in this small 768 sq.ft. abode.
There are a couple things i need to get resolved, so i am posting a drawing which will simplify my explanation of questions.

Bryant Plus 80 Model 310
5 Ton 110,000 BTU
MODEL 310AAV 066110 AAJA
Single Stage - Deluxe Induced Combustion
4-Way Multi-Poise 33"" Tall x 21" wide x 28"deep

(The old furnace is 80,000 BTu. I will be adding the garage which is an additional 300 sq.ft. for a total of 1056 HVAC sq.ft.)

One of my big concerns is that i want to put in a newer central Heating - A/C system , removing the old unit out of it's closet establishment, and putting the new system out in the Garage/Shop

My main concern questions are adequate gas supply and Type "B" venting to the back side of the roof.
Can you increase a 1/2 line up to a 3/4 line for more cu ft.?

Keep in mind that this is slab-on-grade and that the existing gas lines are underneath and coming up through the floor plates and will have to tie into those taking the new lines across the truss chords.

The up-flow furnace will probably be mounted from the garage ceiling between trusses,hanging from the wall, but will detail all that later.

Another question is the "N" Coil
Does it matter if it sits under the furnace in the cold air return stream or ontop, after the heat exchanger into the main trunk.
Bryant "N" Coil; Up-flow - Down-flow

You can see for the most part what i am trying to achieve.

Thanks for all the advice in advance,
Cheers,
Stuart

 

[DEnd]

Do not use the same HVAC duct system in the garage as you do the house. Do not put any duct work from the house inside the garage. Not only is it illegal (not to code) it is also dangerous.

I think you should look closely at a ductless mini-split heat-pump system. With this system you save money by not having to put in new duct work and possibly gas lines, it would also likely have just one outdoor unit for both your house and garage (with "traditional" units you would need completely separate systems for the house and garage) if you condition your garage. Some of these systems put out really good heat down to -13°F.

I gotta question the size of furnace you are putting in, do you not have any insulation in your walls? 110,000 BTU seems excessively high.

If you do decide to go with a ductless mini split you may also consider going to electric appliances and eliminating your gas bill altogether. Induction cooktops give close to a gas cooking experience. In my experience electric ovens beat gas ovens due to their evenness of heat (if you get one with steam and/or convection those are even better). The only real all electric drawback is you don't get endless hot water.

 

[BoostAddiction]

I don't need to run a Manual J to know that 5 tons of AC (is that really what you meant?) is way too much for 768 sq ft.

I agree with the minisplit idea. If you have any kind of insulation in the space, a minisplit will handle it just fine. In fact, my garage of about that size has a 2 ton unit, and it is arguably oversized (it would be if the garage door didn't leak so much).

 

[blackbriar51]

Thats some really great advice guys, much of what i had never thought about, however some of the draw backs are this house was built in 1969 in a low income sub-division outside Seattle,Washington. It can get down to zero but rare, generally it stays in the higher thirties and rarely snows, mostly thick overcast and winter drizzle.

Do not use the same HVAC duct system in the garage as you do the house. Do not put any duct work from the house inside the garage.

Please understand that i am not debative but not understanding.
Why is it wrong to run a branch or drop of heated or cooled air out into an attached garage ?

Not only is it illegal (not to code) it is also dangerous.

Why is it dangerous?
It would help to understand this.
There is no cold air return from garage to draw back into the home.
I have been running an overhead branch drop out here into my small shop for over 20 years.
It is a 12x24 small cabinet shop that has been insulated and sheet rocked , very tidy and clean and has a single 8" overhead drop that keeps it 70 degrees comfortable ,even when it is 20 degrees out.
The fire door from shop to house is completely weather stripped to prevent shop dust from going into the house , heated or not.

I just want to clarify this because of the size of the house the basis of this post was to become informed.

What i want, is to take the old furnace system out completely.
Then install a new smaller 80% efficient system in a " built to code" custom closet out here in the garage with the return cold air duct drawing out of the living room corner as described in the drawing, replacing all the old overhead duct work, essentially what is already up there for the exception of 40 yrs. of tobacco smoke and dust and animal dander inside of it.
It is one of those 1969 things you would have to see to believe, and no they will not be cleaned. Financially it is a very small job.

(Though the furnace closet and furnace will be located out here in the shop/garage giving to more space inside the house without it, the new cold air return will be pulling through the living room, just on the other side of the shop wall, NOT OUT OF THE SHOP ITSELF, just to make that clear if there was any confusion in the drawing.)

I gotta question the size of furnace you are putting in, do you not have any insulation in your walls? 110,000 BTU seems excessively high.

The old furnace is 80,000 btu, that was solely for the house itself 768 sq.ft. and no garage.
It is a giant 1969 dinosaur taking up mass space.
My realtor (a.k.a. contractor ) at that time told me that this old Holly furnace is what was referred to as a "Standard model" house furnace, the smallest they had in 1969.

I bought this 110,000 BTU Bryant unit used, in like new condition, about 4 yrs. old when i got it.
The seller put in heat pumps pulling this Bryant 310 out.
I gave him a $100 for it and $250 for the A/C "N" coil from another seller.
I wanted to at least get the coil established into the duct system while doing this.

The fact is that these homes have old technology, windows, attic and wall insulation. I'm trying to reach balance and unit size less gutting the structure, putting in high tech insulation methods and heating with a Kerosun heater or a 35,000 BTu Coleman Unit out of a goose neck camper trailer. I can come home in dead winter without the heat having ran all day and the thermostat says 55 degrees.

110,000 BTu is it's maximum rating, not what it is going to consume or run at every time it cycles? Is it not? If i opened all the doors and windows when it is -12 degrees , i can see 110,000 or if the house was 3900 sq. ft.?
It still vents on a 4" Type"B" vent....... and not a 5" or 6"inch.

I can put a 1000H.p. Hemi motor into my Ford Lariat and still drive 25 m.p.h. to the grocery store, until i put full demand on it draining .5 m.p.g.
The physical cu. ft. cold air flow and fan are almost the same size as far as air movement.
Fan speed however may be different issue or regulated.

not having to put in new duct work and possibly gas lines,

Why would i have to run new gas lines?
Would this Bryant consume much more than is already there?

electric appliances and eliminating your gas bill altogether.

I understand it is a balancing act, but at the same time, trying to live in both worlds, my panel is only 100amp service and is just about full.
Gas is always going to be cheaper than electric, always, no matter what.

I don't have an issue with labor or materials as long as the desired results are achieved.
I'm also looking at money costs in 25 yrs when i'm no longer able to work.
By the time i get done R value remodeling and have a system that only cycles a few times a day is what i am thinking forward too..

I understand electricity, and how expensive it is. Arguably gas is a far better cleaner comfortable heat. Saws and planers are meant to run on 220v, not house appliances. I'm even cringing over that 220v Jenn-Air 30" wall oven.

Electric is for dwellings where there is no gas service available, in the same as Satellite dishes and no available Cable Television.
As a matter of fact i am posting this over 1969 telephone line technology and a dial up 56K modem. High Speed is great for You-Tube and mass file downloads, but to read the news or e-mail or post to forums?

Respectfully guys, i do appreciate the good advice on the heat pumps and will check into them as an alternative etc. but i would rather detail out the original post and see if there is a positive feasible way of getting this system that i have here $$$ on the shop floor installed, and if not, the code reasons why this design will not fly so that i can sit down and re-evaluate my ideas and what to do next.

I can truly see using a 220v mini-split and understand it's use, but for this application or if i were living in a one room box, say a detached garage? I am at a bit of a loss with your opinions, as a retired professional garage door installer and service tech, i have seen thousands of furnaces in garages all over the P.N.W. Puget Sound region.
Cheers,
Stuart

 

[pseudorealityx]

1. Current code requires a fire separation between the occupied space and the garage.

2. Garages are typically full of smelly nasty stuff you don't want to smell in your house.

3. Assuming you have no return the garage, the air that you supply to that space has to go somewhere. Since the air handling unit has to be even airflow (supply cfm = return cfm), the house is now negatively pressurized, because it needs to draw that air from somewhere. Because your house is old and leaky, it's likely getting some air via infiltration from the garage. IE... just because you didn't put a return in there doesn't mean it's not returning from there.
3a. If it's not pulling air from the garage, it's pulling in outside air through cracks, windows, doors, etc, around the rest of the building, and infiltration is a bad idea comfort wise.

 

[blackbriar51]

1. Current code requires a fire separation between the occupied space and the garage.

This house would not have passed code today or in 1969 if there was not a dividing fire wall from floor to roof dividing living space from garage space.
It is defined as 1/2" sheet rock barrier and a solid core 2 hour rated fire door.
Every garage out here in the P.N.W. with a furnace, it's ducting and mechanical passes through that fire wall into the main house.

2. Garages are typically full of smelly nasty stuff you don't want to smell in your house.

Cold air return would be coming into the furnace from the other side "main house"
Furnace in garage-Cold air coming from living space

3. Assuming you have no return the garage, the air that you supply to that space has to go somewhere.

Typically around garage door and into attic space, i would not get to aggressive about negative pressurized air in an extremely loose environment.
I do not consider some bleed off warm air more than convenient waste with an already overly large system.
Unless i'm out here making dust the shop is clean, the door is open and i have my stand up computer out here in the shop, as comfortable as any other room in the house.

Since the air handling unit has to be even airflow (supply cfm = return cfm), the house is now negatively pressurized, because it needs to draw that air from somewhere.

It draws on itself, it is it's own resource, though i do understand your meaning

Because your house is old and leaky, it's likely getting some air via infiltration from the garage. IE... just because you didn't put a return in there doesn't mean it's not returning from there.

The old furnace, inside the house closet sits up off the slab about 12", that is it's means of circulating cold air return, pushing out as it draws in from underneath .
If it draws through anything it is probably through the old aluminum frame windows. Your statement would be inclusive too, it was drawing off the garage the day the inspector signed off the mechanical inspection in 1969.

If it's not pulling air from the garage, it's pulling in outside air through cracks, windows, doors, etc, around the rest of the building, and infiltration is a bad idea comfort wise.

Dramatically speaking,
If i built a 780sq.ft. home as dust & water tight as a frogs ****, it would literally sweat and mildew everything into nothing over six months and i would be choked out in two weeks.

pseudorealityx
Respectfully, am i to assume? , that National Building Code will not allow mechanical furnaces to be established in Georgia State garages?

 

[DEnd]

Please understand that i am not debative but not understanding.
Why is it wrong to run a branch or drop of heated or cooled air out into an attached garage ?



Why is it dangerous?
It would help to understand this.
There is no cold air return from garage to draw back into the home.
I have been running an overhead branch drop out here into my small shop for over 20 years.

It's dangerous because it will draw air in from the garage. It is basically impossible to have a completely sealed wall between a garage and a house, and the moment a duct is added between the spaces all hope is lost. With central heating and A/C with a duct out to the garage you are depressurizing the house and pressurizing the garage, that creates a pressure difference the wrong way between the house and garage, therefore air (and harmful gasses and pollutants) will travel from the garage to the house. If you place Just the air handling unit (furnace, blower, A/C coil combo) in the garage then it will leak air (there is no such thing as a completely sealed duct system) and do the same thing.
This is also why I have been on here advocating for people to install exhaust only ventilation systems in their attached garages, these systems depressurize the garage pulling air from the house into the garage, this minimizes the chances of garage air (and thus pollutants and harmful gasses) from entering the house through the garage.

110,000 BTu is it's maximum rating, not what it is going to consume or run at every time it cycles? Is it not? If i opened all the doors and windows when it is -12 degrees , i can see 110,000 or if the house was 3900 sq. ft.?
It still vents on a 4" Type"B" vent....... and not a 5" or 6"inch.

I can put a 1000H.p. Hemi motor into my Ford Lariat and still drive 25 m.p.h. to the grocery store, until i put full demand on it draining .5 m.p.g.
The physical cu. ft. cold air flow and fan are almost the same size as far as air movement.
Fan speed however may be different issue or regulated.

Typically with furnaces and A/C units there are one or two settings. every time it cycles it will output at one of the two settings (or a single setting for older units). A/C and heating units typically do not have a way to throttle back the load. It'd be like trying to go 25mph in that 1000hp Lariat with the throttle floored and only using the on/off switch (ignition key) to control the speed. This results in a massive loss of efficiency, and is one of the reasons I suggested a ductless minisplit.

Minisplits have throttling capability so they are better able to match their output with the heat loss/gain in your house. If you get the correct system they can also use multiple heads which may save you money by not needing to use two systems to heat and cool your house and garage.

Why would i have to run new gas lines?
Would this Bryant consume much more than is already there?

Because you are changing the location of the system.

That depends on what your current systems efficiency is. Furnaces take a bit of time to reach their peak efficiency, because it is a bigger system it will likely cycle more. Every time it cycles it will have to warm back up to reach peak efficiency this results in less time spent at peak efficiency which lowers overall efficiency of the system. So a larger system can easily result in noticeably larger gas bills.

Gas is always going to be cheaper than electric, always, no matter what.

That's a fallacy due to a few reasons:
#1 electric companies buy fuel at cheaper rates than you or I are able to.
#2 Well designed heat pump systems can be more efficient from a source fuel perspective than even a high efficiency furnace, especially when newer electric plants are part of the mix. The national average (including transmission losses) for point source fuel efficiency of the electric grid is somewhere around 33-40% (newer gas plants are above 50%). This means as long as a heat pump system's coefficient of performance (CoP) is above 3 then from a fuel perspective it will use less fuel than a furnace will. Financially (depending on how cheap gas is or expensive electric is) the break even CoP for heat pumps can easily be below 3.
#3 Even when you don't use gas you will have a minimum charge on your gas bill. A lot of electric providers also offer a discount if you are an all electric household as well. Getting rid of your gas bill will likely boil down to if you are able to save enough money with a all electric discount to cover your water heating bill.

I don't have an issue with labor or materials as long as the desired results are achieved.
I'm also looking at money costs in 25 yrs when i'm no longer able to work.
By the time i get done R value remodeling and have a system that only cycles a few times a day is what i am thinking forward too..

That's the same way I'm looking at this. My one concern I have with a mini-split system in this instance is that when the unit fails it will likely be a more expensive service call. I think the monthly cost savings will be more than worth it though.

(regarding the furnace in the garage)
If not, the code reasons why this design will not fly so that i can sit down and re-evaluate my ideas and what to do next.

Call your local building inspector's office (I've found the start of office hours to be the best time) and talk to them. Ultimately they are the deciders in chief (so to speak).

 

[blackbriar51]

DEnd, Thank-you!
That was an excellent post, now i'm starting to finally get a good picture on this after all the years gone by.

Tomorrow i am going to try to submit a drawing with all the actual room sizes etc and see if there may be some good suggestions as far as the mini-split systems go, something positive to look into.
Regards
Stuart

 

[LS6 Tommy]

I don't need to run a Manual J to know that 5 tons of AC (is that really what you meant?) is way too much for 768 sq ft.

I agree with the minisplit idea. If you have any kind of insulation in the space, a minisplit will handle it just fine. In fact, my garage of about that size has a 2 ton unit, and it is arguably oversized (it would be if the garage door didn't leak so much).

^^^THIS^^^

5T is about 3.5T too much...

Tommy

 

[DEnd]

DEnd, Thank-you!
That was an excellent post, now i'm starting to finally get a good picture on this after all the years gone by.

Tomorrow i am going to try to submit a drawing with all the actual room sizes etc and see if there may be some good suggestions as far as the mini-split systems go, something positive to look into.
Regards
Stuart

The question now comes to why you are replacing your system. If you are looking for mainly for efficiency upgrades that money is probably better spent elsewhere. Right now the majority of your energy loss is probably through air leaks. There is a general contractor in your general area (Seattle) named Ted Clifton Jr. he has built a few net zero energy houses. ( http://www.tclegendhomes.com/ ) He would be who I would get in contact with to help me find cost effective solutions for reducing my energy bill. He may not take on your project, but he could likely point you in the right direction to people who could help.

On the other hand if your system doesn't meet your needs or needs to be replaced, then more efficient equipment is the way to go. And because many mini-splits are able to throttle to meet loads they are a good choice, especially if you plan on doing efficiency upgrades to your building envelope.

 

[Highbeam]

I have lived here in WA for 37 years now and in almost every house I've ever been in or even houses where I lived the furnace and water heater are located in the garage but ducted into the house. This is not against code. Drawing or discharging conditioned house air to the garage is against code.

Even new houses have the mechanicals out in the garage so as not to waste valuable living space.

My current house is from 1963 and the age is not a problem except for wall insulation. I'm slowly fixing that.