Gas furnace BTU- how much do I need for my home in NJ?

[Zeze]

I'm buying a new house and the seller has agreed to replace their dying furnace which is 50 years old.

The house is 2300 SF, 4 beds, 2.5 bath. I don't know what the BTU is of the current unit at the moment.

1. What is an appropriate BTU needed to heat the home of this size in NJ winter? What's your furnace's BTU of similar homes? (New England folks feel free to chime in). 50,000? 100,000? 120,000?

2. What is the standard AFUE rating I should ask them for? 93%? Or anything above 90 is fine?

3. Any good websites or vendors that assess this over the phone?

 

[Jimzz]

1: Hard to say as its depends on the house. Windows/Insulation/etc... Look at the old one and that rating should give you a rough idea. But around 100k sounds like it might work.

2: Yea anything 90%+ is fine. I try to stay in the 90-93 range.

3: Not that I am aware. I do my own HVAC. I put in a 5ton/125k BTU unit in my NoVa house. 2750sqft and I think 92% on the furnace.

 

[IGBT]

there is a formula that factors the type and R rating of insulation / double pane windows / the number of windows and doors. I ended up with a 80k btu heater thats 96% efficient. I went with York due to the robust heat exchanger and industry standard electronics. They mounted it on a poured in concrete pad and also replaced all the ducting. I also had them install a fresh air intake so I can run the fan in the hot weather and cool the place off at night when the temp drops.

 

[Matthiasa]

The quick estimate of BTU needed is 92000-103500 BTU but that likely assumes average everything, for a better estimate you may need to contact an HVAC professonal.
Alternatively you can take the amount of natural gas used in july in therms which leads to the following:
(therms used annually-(therms used in july*12))*50*(efficiency) to get the load needed.
Where info came from

 

[rsutoratosu]

What does the house have, gas or oil. Steam or water.

Is there radiator in every room, etc. you also need to know the pipe size

ie I have 3 zone in my house, each zone is pipped for 40,000 btu, my furnance is rated for 140,000 btu. with 12% lost in efficiency

http://www.comfort-calc.net/btu_pipe.cfm#Pipe Btu

http://www.calculator.net/btu-calculator.html - btu calculator

 

[John Connor]

Have Con Edison run steam to your house.

That's some awesome stuff there.

 

[Imp]

Depends on if you live in a glass house, a bunker surrounded by insulation, or one with windows open 24/7/365.

I had to do the calculations from first-principles in school, but there should be easier methods that HVAC people use -- and HVAC salesmen can probably draw from experience. Talk to an HVAC salesman?

 

[sdifox]

You need to do an energy audit so you know what you need to upgrade on top of the furnance. Realistically you should just knock the price down a few grands and get a good furnancce yourself.

 

[Scarpozzi]

FWIW, we have similar winters here as you do in NJ (minus the snow), but the weather is usually only 5-10 degrees difference. I had a dual-fuel system installed from American Standard (similar sized home). It features a heat pump unit for heating/cooling and when the temp drops below 40 degrees, it switches to NG. I was able to get by with an 80k BTU furnace that's 92% (if I remember) and it does the job...we survived the freezing temps the last few years...I took some pics of the -6 outside temp displayed on my thermostat with 75 degrees inside temp.

Lots of companies sell similar units because the magic in the system is really the thermostat and thermometer outside switching the heat source. Since my system was a swap (replacing a 40 year system), and no major ductwork was required (except for the new air handler), I was able to get it installed for under $8k. American Standard beat the other quotes I had received....I recommend doing brand-to-brand comparisons and see what makes sense based on distribution in your area.

I agree, you should be the one to order it and install it...have them kick you $7-10k on the unit. That way, you can claim the tax credits and rebates if any are available.

 

[waffleironhead]

Loadcalc.net
Probably will need more info than you have at the moment.

 

[EliteRetard]

If they're paying for it, bigger is better.

 

[waffleironhead]

If they're paying for it, bigger is better.

Not so. An oversize furnace causes many issues such as short cycling. You are better with a correctly sized one.

 

[MegaFlop]

I would try to get a modulating gas furnace and a communicating thermostat if that is a option. It will be a more efficient setup and a modulating furnace will give you some leeway in sizing it correctly. (They usually scale over at least 2x range, ie 50K - 100k btu)

 

[boomerang]

Here's a better way to approach this. You and the seller agree on an allowance amount for furnace replacement. Take that amount off the sale price. Then, you get to put in the furnace that suits you.

I'd rather have something I picked out myself, with the reputation and efficiency rating that I desired and installed by a contractor of my choosing than something the seller had thrown in to satisfy your demand.

When I had my house built the builder had an old furnace that was sitting around the contractor's warehouse that was nearly twice as big as needed put in because he had it done on the cheap. The first time I had a contractor over to look at the furnace, he slapped his hand to his chest and said, who the hell put that big monster in here? That could heat a house twice this size! That, when he was still 15 feet away from the furnace. Yes, it was that much too large.

Don't settle for what the seller wants, get what you want.

 

[Zeze]

Update: We're going to have a HVAC company come and do an estimate. Based on their proposal, that's what's going to be in the contract.

 

[EliteRetard]

not so. An oversize furnace causes many issues such as short cycling. You are better with a correctly sized one.

here's a better way to approach this. You and the seller agree on an allowance amount for furnace replacement. Take that amount off the sale price. Then, you get to put in the furnace that suits you.

I'd rather have something i picked out myself, with the reputation and efficiency rating that i desired and installed by a contractor of my choosing than something the seller had thrown in to satisfy your demand.

When i had my house built the builder had an old furnace that was sitting around the contractor's warehouse that was nearly twice as big as needed put in because he had it done on the cheap. The first time i had a contractor over to look at the furnace, he slapped his hand to his chest and said, who the hell put that big monster in here? That could heat a house twice this size! That, when he was still 15 feet away from the furnace. Yes, it was that much too large.

Don't settle for what the seller wants, get what you want.

MORE BIGGER FIRE!

caps

 

[Mayne]

80,000 btu is fine.... I will install it for 2900 Canadian.

 

[rh71]

2700sf with 5 baths (but really we'll only use 3 max at once) we installed a 104,000BTU and a 55-gal hot water tank. The price differences aren't that big and yes there's the short cycling concern but honestly gas is cheap (even in NY @ $100/mo. avg the whole year) and electric on it is negligible.

http://www.supplyhouse.com/Burnham-ESC4-ESC4-78000-BTU-Output-Cast-Iron-Gas-Boiler (78,000 BTU)
http://www.supplyhouse.com/Burnham-ESC5-ESC5-104000-BTU-Output-Cast-Iron-Gas-Boiler (104,000 BTU)

A whopping $100 difference. Those are direct vent FYI.

Given all that, better to be on the safe side especially if there's potential to expand in the future.

 

[shabby]

I'm buying a new house and the seller has agreed to replace their dying furnace which is 50 years old.

A new house with a 50 year old furnace? Or a new house for you that is 50 years old with the original furnace?
If the house is 50 years old the its insulation/windows are probably on the poor side, so you'll need something bigger, at least 80k.
Also try opting for a 2stage, that way you have a quiet low speed stage and in case you need more heat the 2nd stage can kick in.

 

[Joe C]

Update: We're going to have a HVAC company come and do an estimate. Based on their proposal, that's what's going to be in the contract.

Zeze, there is a lot of bad advice given in this thread. Before you do anything have that HVAC company do a Manual J heat loss on the house. A properly done heat loss calc. will tell you the right size equipment to buy. DO NOT ever just look at the ratings of the existing equipment and replace with similar, most older stuff is oversized for the application wich results in higher energy bills for the owner. Take a look at this site for more information.
http://www.doityourself.com/forum/heating-cooling-air-conditioning-ventilation-t-stat-controls-377/

 

[Greenman]

Zeze, there is a lot of bad advice given in this thread. Before you do anything have that HVAC company do a Manual J heat loss on the house. A properly done heat loss calc. will tell you the right size equipment to buy. DO NOT ever just look at the ratings of the existing equipment and replace with similar, most older stuff is oversized for the application wich results in higher energy bills for the owner. Take a look at this site for more information.
http://www.doityourself.com/forum/heating-cooling-air-conditioning-ventilation-t-stat-controls-377/

Correct answer.

 

[calahan]

it depend of how energy efficiency your system have .... in general it will be around 68K-90K BTU

 

[calahan]

i hope this BTU calculator help you http://www.alternateheatingsystems.com/support/btu-calculator.html

 

[Zeze]

I love you guys. Seriously are there forums like this that provide this level of info and so many various areas of life? Good stuff.

 

[richardycc]

just have the seller give you $5000 back at closing, that should get you a decent unit. you can continue to use the current unit until you've done your research, you might get a few more yrs out of it, why the rush?