need new furnace for 1200 sq. f.t. house

14 years ago

Greetings all,

I've been checking out the site and decided this is a great place to get some expert advice on our looming "new furnace" decision!

We're finally at the point where we're ready to exchange our good ole 80+ year old monstrosity of a gravity-feed furnace! You know, the kind that looks like an octopus and takes up over half the basement?! It's definitely served its time, has been running pretty flawlessly for me for nearly 12 years, but the old soldier is running at lss than 50% efficiencyÂand I'd kind of like to have some basement space!

We're going with a local co. here in WA state that carries Lennox and is highly regarded with BBB, our power company, etc. My question is this: with relatively mild temps year-round, a fairly small 1.5 story 1921 home (1200 sq. ft.), insulated attic/basement ceiling/blown-in wall ins. and new vinyl, double-paned windows throughout the house, which would be the better furnace: the Lennox G71MPP-36B-070 furnace or the G71MPP-36C-090?

The rep has recommended the 70 over the 90, but with no way to heat the top story (no place to run ducts) we're concerned that the 70 wouldn't do as good a job as the 90. Right now we seal off the stairwell and use space heaters upstairs to warm up the bedrooms in cold weather.

We like the idea of a smaller, less-expensive furnace, but want to make sure it's going to meet our needs. We'll also have a vent for our unfinished basement, too, so we can eventually heat it when we convert it to a workshop space.

Any thoughts? Oh, and the furnace is gas-powered. Also, thermostat thoughts are most welcome!!

Thanks so much for any thoughts and recommendations!

geargirl

Featured Answer

baldloonie

14 years ago

70 and 90,000 BTU 95% furnaces for that small of a house in a mild climate both seemed very oversized.

These furnaces need to move a LOT of air to be efficient and variable speed blowers have the get up and go to do it. Could be very loud.

If you go that big, better off skipping insulating and new windows, you need all the heat escaping you can.

Sort by:Oldest

Comments (6)

snoringcow
14 years ago
It's hard to do anything but throw a rule of thumb heat loss calc without a whole lot more info. Old houses are tricky and without a visual inspection of your actual R values, window area, construction type, exposed wall areas, etc. it isn't possible to come up with much in the way of accuracy. But in a well or fairly well insulated home such as described and with the improvements you've described, probably the 070 (that is the part of the model number representing the btu input) will put you comfortably above the load required. Not being at hand familiar with the model nomenclature of Lennox equipment, (I never joined their "club") I'll assume that this model represents an at least 95% AFUE, condensing gas furnace of some configuration. Increasing the size or oversizing your furnace to compensate for a non-ducted upper floor area will do you more harm than good. Oversized furnaces, in spite of their duct system - or lack of it - will short cycle (start and stop frequently) which is wasteful in terms of energy, dissatisfactory in terms of comfort, and hard on components, especially ignition systems.
Ask your installer for ideas to get some duct upstairs. Oftentimes some thought and imagination can find a way. But I'd go with his recommendation as far as size.
Think of your furnace as you would an automobile. Short trips around town are bound to do it more harm and use more fuel than long treks on the open road.
energy_rater_la
14 years ago
also if you seal the air leakage in the house it will be easier and more affordable to heat and cool.
have you had any hvac companies out to look at your home?
Related Discussions
One Furnace or Two - help needed for new home construction
Q
Comments (10)
The infinity system is an automatic zoned system. There is so much more to it that you describe. But from the user standpoint, I'll give some examples. Each zone has a stat. The master stat can change temps for the different zones. Each zone can turn on the system. A basic manual damper system might only direct air when the system is on but couldn't turn the zone on from anywhere. The best example is with basements in shoulder seasons. We don't run the heat here in late March but the basement is cold still. In a simple system, the basement dampers might be all open but it can't call for heat so it stays cold. Now in January, it can direct all the heat it wants (to a limit) down to the basement so it is fine. The Infinity system measures the pressures in the air handler and cuts down the motor if they get too high. So if a small zone is calling for heat, it runs the motor at a lower speed. This eliminates the need for dump or bypass zones. Inifinity stats are small computers that are shockingly more sophisticated than the stats you see in 95% of homes. Not simply programmable but a lot more. They have LCD screens and menus. They tell you when the filters need to be changed. They have digital humidity readouts. They can set heat pump/furnace cutoffs. etc etc The zone dampers on an infinity system relay back their position to the controller. So it isn't a simple relay and a command to open a damper. It is a nearly foolproof system. No one can give you an Inifinity system for $1200 unless they don't know what they are doing and lose a chunk of money. I paid about $3000 per floor.
...See More
Advice needed. Need A New Gas Furnace
Q
Comments (54)
GoTerps let's look at each system's numbers. option #1 3929268 Active Systems XC14 SERIES LENNOX INDUSTRIES, INC. XC14-024-230-02 CX34-25+TDR SL280UH090V36B* 24000 13.20 16.00 option #2 3929121 Active Systems XC14 SERIES LENNOX INDUSTRIES, INC. XC14-030-230-03 CX34-31+TDR SL280UH090V36B* 29000 13.50 16.00 option #3 3656259 Active Systems COMFORT 16 PURON AC CARRIER AIR CONDITIONING 24ACC624A**30 CNPV*3014A** 58CV(A,X)070-12 23000 13.00 16.00 1 option #4 3656288 Active Systems COMFORT 16 PURON AC CARRIER AIR CONDITIONING 24ACC630A**30 CNPV*3117A** 58CV(A,X)070-12 28400 13.00 16.00 1 all qualify for tax credit. three observations. 1.The Lennox furnace is oversized and should drop down to the 70K model. 2.It is important that lineset be sized correctly whether you select 2 ton or 2 1/2 ton condenser. Flushing is acceptable practice but refrigerant lineset size must be correct. If you elect the 2 1/2 ton condenser, it is unlikely that old lineset will be correct size 3.I do not like thermostat selection for these quotes. I would like to hear from Ryan's ideas/suggestions on this. I do recommend a good 4-5" box filter cabinet. I would not put down more than 25% upon contract acceptance. now to the fuel comparison between electric vs nat gas. to be fair, I will use 50 therms mthly usage to better average your nat gas mthly base charge. Cost per 100,000 btu of useable heat Heat Pump with COP of 2.75 $1.15 Nat Gas Furnace 80% eff $1.81 you can readily see that a HP above temp balance pt is the less expensive choice to heat your home. Keep in mind the main reason for the large difference is the 80% eff furnace. yes, if operating costs are important to you, then HP operation would save you some $$s. ask dealer for option on HP condenser version if interested. IMO
...See More
New furnace for circa 1906 house
Q
Comments (6)
A manual J is definitely in order. The two 90s will put out about 81,000 BTU maximum; the Carrier 100 will put out about 95,000. Their next lowest unit is an 80 which will put out about 76,000 BTU. All three units may be oversized; the 80 could be adequate, pointing out the need for the heat calc. As a comparison, I'm in the Philadelphia area with a larger house (20 year old), 2 story, 2500 SF. It requires 60,000 BTU at design temperature. You should try to make as many improvements to the home's envelope before updating your system (and before the heat calc). Will benefit your heating and cooling needs What is your nearest large city? V
...See More
convert 1200+ sq ft. of delaware river rock yard to grass
Q
Comments (12)
Marcj117 is there anything at all that you like about the rocks? Do you know what is underneath the rocks? I want to encourage you to at least remove some near the front of your house, but it will be time consuming and tedious. It took me around three days to move rock from one side of the yard to the other side of the yard (luckily it is not my yard). It was a small amount of rocks. Around twenty years ago my neighbor decided to have a river rock yard with just a small area of grass. She also had a wonderful Cedar tree close to my property line. It all looked hideous so I won't go on about that. I wasn't watching the calendar so I do not know how many months passed before the weeds arrived. They just sprout above the plastic. She was long gone by then. The house has changed owners a few times since then. My current neighbor does not weed weekly. About every three months she and her family clean the area. It is not the weeds that are so messy, it is needles from the tree. The needles get stuck in the gaps between rocks. On my side under the tree there is an area too shady for most plants to grow. I keep it as an unplanted area. I rarely get weeds because I leave the needles on the ground. I am very grateful for the free mulch.
...See More
geargirl
Original Author
14 years ago
Hello all,

Thanks so much for your input. Yes, we've been making improvements to the house over the years, which includes new vinyl windows, insulation, a new door and we're working on sealing up various air leaks as well. :) Now we're pretty snug during the winter, and I'm sure we'll be shocked how much more comfortable the house is (not to mention cheaper gas bills!) once we get our coal/oil/gas old timer furnace replaced by a new one!

I've had a couple of HVAC companies out, and we've pretty much decided on the company that carries Lennox. Their bid was better, plus we can get some rebates through going with them via Costco, so we're feeling good about the install. I was just wondering about the smaller furnace, but snoringcow confirmed what I'd been suspecting, so I'm sure we'll be happy with a slightly smaller model.

My last question: is the Honeywell Vision Pro IAQ thermostat a good choice, or should we request another model? This forum has taught me that thermostats are also something to be considered, so let me know if there are more suitable models out there. However, we're not doing AC, so maybe the thermostat issue is not an issue at all! But, just thought I'd toss that out there for y'all, just in case.

Thanks again!

geargirl
geargirl
Original Author
14 years ago
Baldloonie,

The furnace's BTU is 63,000, so I think we're OK. Plus, the furnace is in the basement, which we use primarily for storage and working on crafts, etc.

geargirl
paulbm
14 years ago
Do you have the paper white asbestos on your ducts that are going to be removed, if so what is that costing. later Paulbm

need new furnace for 1200 sq. f.t. house

baldloonie

Comments (6)

snoringcow

energy_rater_la

Related Discussions

geargirl
Original Author

geargirl
Original Author

paulbm

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

need new furnace for 1200 sq. f.t. house

baldloonie

Comments (6)

snoringcow

energy_rater_la

Related Discussions

geargirlOriginal Author

geargirlOriginal Author

paulbm

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

geargirl
Original Author

geargirl
Original Author