Home BTU Requirements?

[afblue]

When I first selected my fireplace insert I did a crude and completely unscientific method for calculating the size stove for my house. I basically said " my house was built in 1922 so its old not much wall insulation, but has new windows, and a massive attic blanket. My wife complains alot about being cold, yet will never complain if she has to take clothes off *wink wink*, and will just open the windows a little. I have a large fireplace so whats the biggest I can go? So it was down to a PE summit, and Quadrfire 5100i. Both had a great reputation, but saw a 5100i in person and only a summit in a brochure. So here we are QF5100i being installed in 28 days.

I do not question my insert purchase, (nor can I its already paid for) but I wonder, what is the actual calculation to what will fit my house? I was an easy sell for the dealer, because I said it first, isnt it just the biggest one I can fit in my fireplace?

I found this website: http://www.uppervalleystoves.com/index.php?option=com_content&task=view&id=15&Itemid=33
I wont trust the validity of it because I have no real world experience, but its worth a discussion for what you guys think. My house I entered with #2 house(double pane windows r28 ceiling r12 walls and average leakage , cold climate, 1700sq ft and 8.2 ft ceilings. It spit out 33,525 BTUs and maximum of 67,051 BTU/hr So my 5100i pretty much fits 30,000 realistic average, max 71,500BTU/hr. According to QFs zone chart I would require 22,000 BTU/hr for 1700sq ft.

What do you guys use when calculating?

 

[fbelec]

just took a look see at the quad 5100i that has a 3500 square foot heating cap. realistic maybe 3000 sq. you my friend are going to cook yourself right out of the house. the pain about having a stove that is to big is the shoulder seasons. when it's not so cold yet but you need a fire to take the chill out. my stove is to big for my house and i can say it's a royal pain in the seat when you need just a little heat. even normal winter temps can be work because during the day when you have some solar heat from the sun the house bakes.

anyway the key for you will be a hot fire with small diameter wood not filling the firebox more than a third. just for chill chasers.

congrats on the stove. my nabor has a 5700 and love it.

 

[LLigetfa]

I doubt the stove is too big for the home. You can build small fires in a big stove but cannot build big fires in a small stove. Better to have it and not need it than to need it and not have it.

Mine is 3.1 cu ft heating a 98 vintage 2200 sq ft home and I wish I had the next larger size. It's not that it cannot heat my home because it can, it's just that it takes a lot of work to manage the coal buildup and hard to get long burn times.

 

[Corners]

What are you heating with now? If it's an oil/gas/propane furnace, check the label and see what it's rated at.

 

[Bigg_Redd]

There is no calculation.

You could heat your home with a candle if it's insulated well enough.

A large stove/insert is probably the best you're going to do with a 1700 sq ft house built in 1922.

 

[woodgeek]

Easy--if you know the BTU output of your furnace, and time it cycling on and off, you can figure your demand at a given outdoor temp. The BTU figure on a furnace will usually be 'input' BTU, so the output will be the number on the sticker times a nominal efficiency. Mine is 137,000 BTU/h (1.0 gal oil per hour) * 80% = 110 kBTU/h. When it is as cold as it gets here (5F) the furnace runs about 45% of the time, so my max demand is 50 kBTU/h. At typical January temps (25F), my demand is proportionately lower, about 35 kBTU/h.

This tells me I need 35 k output wood stove to do some serious supplementing, 50 k to heat by stove alone.

Or, if you know how much you are spending on fuel/ or elec for heat, you can divide that number by the number of heating degree days in your location (available on the internet) and work it from that angle...

But, as you've been advised, it is usually better to be a little too big than too small or even 'just right'--longer burn times, pushing the stove less, etc.

 

[lexybird]

I doubt the stove is too big for the home. You can build small fires in a big stove but cannot build big fires in a small stove. Better to have it and not need it than to need it and not have it.

good point!

 

[SolarAndWood]

One method is to look at the fuel you actually consume with your furnace. This might be low if the wife is complaining about it being cold. Although, if your stove is going where she spends most of her time, it may actually be high. We burn a lot less wood than the previous owner burned in propane and the main living space is warmer.

 

[fbelec]

I doubt the stove is too big for the home. You can build small fires in a big stove but cannot build big fires in a small stove. Better to have it and not need it than to need it and not have it.

Mine is 3.1 cu ft heating a 98 vintage 2200 sq ft home and I wish I had the next larger size. It's not that it cannot heat my home because it can, it's just that it takes a lot of work to manage the coal buildup and hard to get long burn times.

the pain about having a stove that is to big is i have to do alot off starting a fire from scratch. the only time i can keep it going 24/7 is when it's in th 20's during the day. otherwise i'm starting a fresh one everytime. my house has old insulation in the walls 1.5 inches. same in the attic. i have a 1280 square foot house with a stove rated at 2400 square ft. he has a 1700 square foot house and a stove rated at 3500 square ft. and he has better insulation than i .

yes there is a advantage to having a bigger stove, but if you think that it is a pain in the seat to start a fire each time and have to wait for things to come up to temp then it's not good to have a stove that much bigger. his is not the next size up but 2 or 3 steps up.

ll i guess it's all on how warm he likes his house. i like my house in the lower seventies. there is another thread about the defiant 1 that i been going back and forth with a guy that's running his house at mid to upper 80's. he loves it. i would die.

 

[afblue]

The house now has a 15 year old high efficiency furnace, running on Natural Gas. I unfortunately have only seen my own house once a month for 3 days at a time since we bought it in August because I have been in Georgia for military training until Nov. So I dont have the luxury of running in the basement and getting specs off the furnace. The house is very sound, but again being 1922, plaster lathe walls I doubt there is any insulation in the walls. The windows are new 5-7years double pane low E coated, but I have alot of them 34! The more I think of it the floor plan is pretty closed off so heat distr is going to be somewhat of an engineering feat. But the house originally had a gravity coal furnace, so all the vents and ducts are oversized, so I am looking to chase them with a smaller flexible ducting in the the cold air returns so I can independently draw the air from upstairs into the living room and create a thermal loop up the stairs, and not effect the normal operation of the furnace.

When I say that the wifey is cold, its not that we keep the house super cool, but 70ish. She would be just fine with it being 80 in the livingroom and kitchen, and I am mostly tinkering in the garage or basement so I would be out of the bllast zone. Upstairs I would like 65deg and she is used to me tossing the comforter on her side becuase I am too hot.

The Insert sizing we came up with was I wanted a firebox that was large and could fit most any size log in. In the dead of winter we will still have a decent burn time when the fireplace was running on the higher end. There were plenty of medium sized inserts that would have been "ideal" aka the numbers "matched" Lopi Freedom, Avalon Olympic, Hampton 300i, PE Vista, and Quadrafire 4100i. But we wanted to error on the side of warmer, and I will have to be creative in the shoulder season. I have some techniques up my sleeve, Using more firebrick to reduce the firebox size, lower BTU wood. We have an Amish lumber mill across from my fathers land where we harvest and store our firewood, So I have an unlimited "free" supply of slab wood, and yes I will say it, its mostly pine. I wont use it this year but I will have it very well seasonsed for next so it will burn clean.

Pics always help: Sorry I dont have any of the fireplace:

 

[LLigetfa]

I know what a PITA starting daily fires can be, I do it almost every evening during the heating season. Last Winter I did quite a bit of 24/7 burning when gas prices soared but the wife said no to 24/7 burning this Winter. I would time cleaning out of the ashes to coincide with outside temperature, leaving in more ashes in mild weather. More ashes means less heat extracted and coals last longer so fewer reloads. I remove more ashes when it's real cold out so that I have more room for wood, get less coal buildup, and get more heat from the stove. As mentioned, it takes a lot of careful tending to get good constant heat out of the stove and not get a buildup of coals.

 

[spirilis]

I found a site that helps you compute this-

http://www.herman-nelson.com/btu_calculator.cfm
actually that seems to be meant for portable heaters in specific spaces, not sure if that factors insulation or whatnot... but it might give a ballpark?

Heh, nevermind, the link in the OP is probably better than this

 

[afblue]

I found a site that helps you compute this-

http://www.herman-nelson.com/btu_calculator.cfm
actually that seems to be meant for portable heaters in specific spaces, not sure if that factors insulation or whatnot... but it might give a ballpark?

Heh, nevermind, the link in the OP is probably better than this

Yeah I just checked it out, that formula just shows how much BTU is required to bring a certain volume to temp, but doesnt account for insulation and maintaining a tempurature. But its all good, nice to see everyone else is finding other things on the net....

 

[RustyShackleford]

Easy--if you know the BTU output of your furnace, and time it cycling on and off, you can figure your demand at a given outdoor temp. The BTU figure on a furnace will usually be 'input' BTU, so the output will be the number on the sticker times a nominal efficiency. Mine is 137,000 BTU/h (1.0 gal oil per hour) * 80% = 110 kBTU/h. When it is as cold as it gets here (5F) the furnace runs about 45% of the time, so my max demand is 50 kBTU/h. At typical January temps (25F), my demand is proportionately lower, about 35 kBTU/h.

Yep, in fact you should be able to calculate a single figure for your house: BTUs per hour per degree fahrenheit (of differential).

Or, if you know how much you are spending on fuel/ or elec for heat, you can divide that number by the number of heating degree days in your location (available on the internet) and work it from that angle...

You might even be able to get a little more precise, if you have natural gas and it has a meter like an electric meter.
See how much gas you use in a 24 hour period with the thermostat at some constant setting, try to compute the
average outdoor temp during that day ...

I can't do this, using propane (which my good friend Hank Hill delivers to me regularly); the tanks have a very crude gauge.
Oil tanks are probably the same.

 

[fbelec]

Easy--if you know the BTU output of your furnace, and time it cycling on and off, you can figure your demand at a given outdoor temp. The BTU figure on a furnace will usually be 'input' BTU, so the output will be the number on the sticker times a nominal efficiency. Mine is 137,000 BTU/h (1.0 gal oil per hour) * 80% = 110 kBTU/h. When it is as cold as it gets here (5F) the furnace runs about 45% of the time, so my max demand is 50 kBTU/h. At typical January temps (25F), my demand is proportionately lower, about 35 kBTU/h.

Yep, in fact you should be able to calculate a single figure for your house: BTUs per hour per degree fahrenheit (of differential).

Or, if you know how much you are spending on fuel/ or elec for heat, you can divide that number by the number of heating degree days in your location (available on the internet) and work it from that angle...

You might even be able to get a little more precise, if you have natural gas and it has a meter like an electric meter.
See how much gas you use in a 24 hour period with the thermostat at some constant setting, try to compute the
average outdoor temp during that day ...

I can't do this, using propane (which my good friend Hank Hill delivers to me regularly); the tanks have a very crude gauge.
Oil tanks are probably the same.

nice looking house. can the firebrick idea. you do more off setting of how it burns than it's worth. just do small fires.

 

[afblue]

Easy--if you know the BTU output of your furnace, and time it cycling on and off, you can figure your demand at a given outdoor temp. The BTU figure on a furnace will usually be 'input' BTU, so the output will be the number on the sticker times a nominal efficiency. Mine is 137,000 BTU/h (1.0 gal oil per hour) * 80% = 110 kBTU/h. When it is as cold as it gets here (5F) the furnace runs about 45% of the time, so my max demand is 50 kBTU/h. At typical January temps (25F), my demand is proportionately lower, about 35 kBTU/h.

Yep, in fact you should be able to calculate a single figure for your house: BTUs per hour per degree fahrenheit (of differential).

Or, if you know how much you are spending on fuel/ or elec for heat, you can divide that number by the number of heating degree days in your location (available on the internet) and work it from that angle...

You might even be able to get a little more precise, if you have natural gas and it has a meter like an electric meter.
See how much gas you use in a 24 hour period with the thermostat at some constant setting, try to compute the
average outdoor temp during that day ...

I can't do this, using propane (which my good friend Hank Hill delivers to me regularly); the tanks have a very crude gauge.
Oil tanks are probably the same.

nice looking house. can the firebrick idea. you do more off setting of how it burns than it's worth. just do small fires.

I am remembering some thoughts I had from before after LLigetfa posted above. When the fires need to be smaller its easier if the ash bed builds up a little. And I probably wont waste my time buying excess fire brick. What I am looking for is a small manual splitter setup I can keep in the garage or basement to break my splits down smaller, because I know my father's Eye Ball "O" Meter for his smoke dragon stove are going to be too large for my EPA insert, and I have to get them smaller for this year, till I can split my own wood for next year.

This is an old but only pic I have of fireplace for now. Its when we first bought house, now its completely stripped clean, decor, sheet covered couch, wall paper and sage green carpet gone. The hearth is also redone, With Slate tile the width of original hearth and out 30". Inner 20" original mortar bed was replaced with 3.75" of Hardibacker Board and slate tile for an R-1.97 (min 1.16 needed) further 10" out is 3/4" hardi and slate for ember protection, and blended into circe 1922 oak flooring. Stove will be QF 5100i with Nickel trim and mantel deflector.