O/T: Furnace question

I'm doing some basically free work for a friend. She needs a new furnace. The existing unit is a converted coal burner; not reliable or safe. She can't afford a heating contractor. I've done some HVAC stuff before, but I'm better with framing and remodeling. I want to make sure I get this right.

She has a 6 room, 800 sq. ft. house(25 x 32). She may, at some future time, want to create usable space in the attic. For climate purposes, the location is Vandercook, MI.

It will be a natural gas unit, installed in the unheated basement area of the house.

My questions are:

Is a 40,000 BTU adequate? From research I've done so far, a 30,000 + is the recommended minimum. Will this be enough IF the attic space is utilized in the future?

Are 6 vents, size 4 x 12, going to provide enough air flow? She'd like to have one vent in each room.

There is a centrally located 12 x 12 vent that I can use as a cold air return. Is this big enough for a 40,000 BTU furnace?

Insulated flexible duct vs. rigid metal duct? Given that the basement will be unheated, my best guess is that the flex duct is a better choice.

There is currently a chimney into which both the gas water heater and existing furnace are vented. Code no longer allows this. I'd prefer a power vent furnace due to ease of installation. Am I making the wrong choice?

Thank you for your time; I appreciate your opinions and suggestions.

Sincerely,

Anthony

I understand helping a friend and not having much money. However, there is a good reason the HVAC folks make the money they do - it takes experience and education to properly answer your questions. It is not economical or safe to do that kind of a job by trial and error.

If you are determined to do this-----I would contact the local gas supplier and ask them for some specs.

You may even get useful info from someone that sells furnaces.

If you've got to buy a furnace and run vents, why not look at hydronic (??) heating? You could heat heater water and hot shower water with the same unit and only need one chimney. It would (I think) be easier to run water pipes and hang radiators than run vents, worry about filters, dust, return air, animals eating/dieing in duct work, etc. Don't know what stuff in your area costs. Just a thought, you can be pretty creative.
Dave

Cheapest by far and least likely to get you all in trouble?
Cap the stove smoke stack tight and use the existing coal fan and duct work. Add a couple of resistance heaters into the hot air plenum for basic house heat. Put a baseboard heater with it's own thermostat in the room and near where she spends most of her time.
Don't put the furnace thermostat near the baseboard heater's thermostat.

The size is not far off, but might be a bit low. Depends on the windows and wall insulation values. If well and tight windows with storms or double pane, It should be great. If leaky, go to 45 or 50K. I also recommend a condensing furnace with a efficiency rating well into the 90s. The cold air return is basically too small at 12X12. It should be more like 18X12. The higher blower forces needed with small ducts and returns, are going to make velocity in them highenough to make noise. Your install should be quiet, especially if there is a dual or variable output combustor. The intake "Square inches of the plenum should be used to judge the sixze of the intake side. Use an electronic programmable thermostat. Use of a condensing furnace removes the exhaust from the need for a chemney (See local codes) and will require a drain or pump to drain, for the condensate, and an air intake pipe from the external air (out of the house) The intake and exhaust are usually 2" or 2.5" PVC. Have a gas professional check the piping for code, and get a permit. Loosing you entire capital goods to a lawsuit does not equate to a good tactic if things go wrong W/O the permits, and inspection. JimN

Why not look into modern space heaters? With such a small house you might only need 3 or 4 max, they are 99% efficient, take up very little space, are independently programable and require a half-inch gas line(less floor penetration).
I have them in my mtn. house and am very impressed with how efficient they are. Go for the good ones like Rinnai, etc.

Sealing air leaks around windows and doors. And doing something about that cold basement chilling the floor above it would help too.
What is the price of natural gas, oil, LP and electricity in your area? Can you get stoker coal? Harman makes a very good coal stoker.

Why not fix the old one? What is it gravity octopus. Millivolt system? Only have 3 or 4 parts. No motor, no blower,no electricity. Pilot generator and burner, valve, tstat, hi limit. Insure with gas company. I had one like this gas company inspector on hourly fee, said was pretty bad. I got their insurance and the same inspector said it had a lotta life left. If your furnace is not one of these, delete this story and replace with simple forced air, pilot light unit more like 70 or 80 thousand btu. Vent free space heater? I would only use one in basement about 5 - 10 thousand btu. Warm floors mean a lot. More than 5 - 10 thousand btu in some houses make breathing difficult for some people. I would suggest strongly inspections and permits, unless you are really confident and live in this house, too. As electrical contractor, I have done lotta furnace work and over 40 years at least 3 times I would have been sued for someone else's work. Blame in a claim goes to last person to work in house if they have good lawyer. Homeowner's permit is way to go if you or she can get it.

Hi Anthony,

There comes a time in ones life where one has too know there limits of trying to help someone. You have just reached those limits from reading your thread.

Too try and explain everything you would need to know too complete this job correctly, would take many pages and hours to just explain the final tests that need performed before a new unit start up.

Not only are your putting your friends life at risk, your also betting your net worth if you were negligent on the installation, more probable than not.

A possible solution to help your friend, would be too seal all the air leaks around the doors, windows and structure. Maybe adding some cellulose insulation to the ceiling and fiberglass batting to the walls or flooring.

If the windows are single pane, then make a temporary inside frame from 1x2 with a layer of plastic for a double pane window.

This alone should make a "old" unit perform like a brand new unit plus save her a ton of money in utility costs even if a new heating unit is required.

T_Bone <---Retired HVAC&R Engineer

I have a rental situation with identical specs. It has a ducted 35k Empire wall furnace with slightly higher pressure ducts that run along the exterior walls like baseboards. It's a sweet simple safe setup. Located in the heated space, it even has ducting going up to a second story but that involved a false wall concealing the ducting. It's 40 years old and still good as new. They're sill available.

Just went to the Empire site but couldn't find a similar model. Sorry

I didn't think of the obvious at 1st.
With the water heater, the place already has an approved "boiler" already connected and paid for.
Just add a water pump, heat exchanger and airmover.

As previously asked, is the existing furnace one of those old time gravity octopuses that are mostly seen in movies and museums?
For backup heat incase what ever heating system goes down but if the electricity is still on. Add baseboard heaters in the bathroom, kitchen and basement where the pipe are to keep the pipe from freezing.
Adjust the thermostats as required. 50F for backup heating if the main heat fails.
If she keeps the rest of the hose cool, she can dial the bathroom baseboard unit up. And only heat the bathroom toasty warm if wants to keep from freezing while bathing. And the bills down

It's definitely an octopus. Round, at least 4' diameter and about 5 1/2' tall. Only 4 heat ducts coming out of it; one 12" and three 8". Seems to be in decent shape for it's age overall, just no longer reliable. I had to have to bust it up to get it out, but the basement steps/door are only 32" or so. Looks like they installed the coal burner, then built the house over it.

I'll call the lady and get a couple pictures of it.

Thanks,
Anthony

> Looks like they installed the coal burner, then built the house over it.

Haha. It sounds just like my wood/coal furnace. Mine is composed of about 5 seperate pieces of cast iron. You can disassemble it to move it, but each piece still takes 3 men to move. On the front it says "Sears Indestructo". This is not a marketing ploy, it is fact.

If you're planning on taking this monster out, I recommend taking the time to take it out without busting the cast with a sledge (what most HVAC guys do). You can't find cast iron furnaces this size anymore and anyone who knows about them would take them over modern firebrick stove any day.

Just leave the duct work and pull the furnace out from underneath.
Working blowers and cabinets from deceased furnaces units from tossed away at the dump all the time.
Have a tin knocker connect the blower to the old pipework. Add the heat exchanger which in plumbed into the water heater. And add a stat to start the boiler pump and blower fan when heat is required.
What is she using for heat at the moment?

Got some pictures.

<a href="http://s215.photobucket.com/albums/cc131/Kylezdad/?action=view&current=old1.jpg" target="_blank"> </a>

<a href="http://s215.photobucket.com/albums/cc131/Kylezdad/?action=view&current=P1010124.jpg" target="_blank"></a>

<a href="http://s215.photobucket.com/albums/cc131/Kylezdad/?action=view&current=old3.jpg" target="_blank"></a>

A couple more questions:

How much difference does it make if you use the humidifier on this thing?

Does anyone know of a source for repair parts for the conversion kit? Or a newer, better conversion kit?

I like the simplicity of this design. No moving parts, circuit boards, etc. If this unit could be made safe and reliable, is it worth keeping it in service?

Thanks,
Anthony

Hey, tjdub, I just purchased the same stove. I am starting to assemble it in my carwash to heat floors. Mine was a steam heater. Was wondering if you have any info Manuals etc on these stoves? Do you know where to get info?

Anthony there is one serious flaw in the idea of keeping the old girl in operation. That is the integrity of the firebox, and the possible leak of combustion gasses into the house. There is no high value reason to use the old furnace. A Trane, Or Lenox, Or other brand name high efficiency furnace will be in the 1500 to 2500 range of cost, and will be massively better at heating the home. Doing it with a conversion leaves you with liability (in the face of friendship) that does not pay.
When removing the sheet metal wear a respirator, and do not break up the asbestos, leave it intact.
Dispose of it with hazardous waste facilities.
The new furnace will pay out in both comfort (with a humidifier system attached), and in fuel costs.
Electric anything will boost the profit of the utility company more than twice the price of the gas it would use in a good modern furnace. JimN

Hi Anthony,

Adding humidification too 50%rh will make a human feel like you turned up the t-stat 4ºf during the heating season. If you were at 50%rh then you would need to increase the room too 85%rh for the average human to feel the difference.

The controls shown in your pics are common to the industry and easy obtained at any HVAC supply house.

If the existing unit was 80% efficient and a new unit was 90% efficient with a utility bill of $150mth that can be applied just too room heating, then it would cost approx $75yr more to heat with the existing unit.

You have a can of worms with the existing unit as I'm pretty sure there will be some asbestos in the gaskets alone and maybe in the plenum wrapper. This will require special permits and a company certified in asbestos removal too remove this unit and dispose of the hazardous waste. The homeowner will be temporary relocated until the work is completed.

You would confirm updated State/Federal laws on asbestos as I've been retired too long.

How bad is asbestos? I worked with a engineer who took some field measurements on some asbestos piping. Unknown to him, he was highly allergic too asbestos and 6mths latter he was dead from fibers that he had inhaled during the measuring.

Plan "B" might be a choice here. Leave the existing unit alone and start thinking of adding dedicated room heating if needed.

T_Bone