DIY Heat Loss Calculator?

Vermonter_2

Can anyone recommend an accurate DIY heat loss calculator? I've got to do the math for an electric baseboard in a spare bedroom.

Thanks in advance!

Vermonter

Charlie from wmass

Weil McLain has a booklet

http://www.weil-mclain.com/en/multimedia-library/pdf/weil-mclain-pdf/other-downloads/easy_loop.pdf It will at least get you close for btu loads.

Vermonter_2

Great Info

Unfortunately the smallest area in the chart is 500sq.ft. Is it reasonable to do the calculation for the floor (the whole floor is about 600sq.ft.) and then take a fraction of that for the bedroom itself (about 120sq.ft.) or will I be way off when trying to do heat loss for such a small area?

Thanks,

V

meplumber

What part of Vermont?

How old is the house?  How many and what size are the windows?  How long and tall are the outside walls?  Is the floor above a heated space or unheated basement?  Insulation?  Is the ceiling on an attic or is heated space above?



Maybe I can give you some numbers to guide you.

Jean-David Beyer

I have a different Weil-McLain booklet.

The one I have is similar to the one posted here, but is different in some respects.



http://www.weil-mclain.com/en/multimedia-library/pdf/weil-mclain-pdf/other-downloads/boiler_replacement_guide.pdf



I did not like it much, because I had to make even more assumptions than when I used the Slant/Fin computer program. I liked the procedure in John Siegenthaler's book, but I was too lazy to do it explicitly, and used the Slant/Fin program instead.  For example, I could not figure out how to enter data to account for radiant heat in the slab on which the house was built. Even if I knew how to enter it, I did not know if it is insulated beneath the slab, or along the edges of the slab, and that likely makes a difference.



I actually computed my heat load three ways.



1.) My old oil burner had a 1/2 gallon/hour nozzle, so I figured 70,000 BTU/hr input, maximum. The house always (in 33 years) got enough heat, so that was an upper bound on what I needed.



2.) I used the Weil-McLain booklet I show above, and got 36,250 BTU/hr.



3.) I used the Slant/Fin program and got 29,234 BTU/hour.



I do not know if any of these calculations give the boiler input (not a good idea, IMO, because I would need to know the efficiency) or the boiler output. But given the variation in the numbers, that I assume are due to the various assumptions I had to make for each procedure, it may not matter. Since I knew I was going to get a W-M Ultra 3, these calculations all told me to get their smallest model., and wish they made a 40,000 BTU/hour (or so) model.

Charlie from wmass

close enough for electric base board

while other methods are more accurate for heat losses this is here, free, and simple enough. I would do the fraction of the floor as you were planning. you can also use the other link for weil mclain. The electric base board company probably has a chart available. Or take me plumbers kind offer. By the way what heats the rest of the home?

meplumber

Thanks Charlie.

Wow.  I missed the electric baseboard part. 

Vermonter_2

A few answers and a few more questions...

What part of Vermont? SE corner... first three digits of the zip are 053.



How old is the house?  1968



How many and what size are the windows?  We're planning on remodeling the first floor. Our plans currently call for two small windows on the North wall, approx 20"hx40"w each, and one large window on the West wall, approx 50"hx60"w.



How long and tall are the outside walls? Again, remodeling, but plans call for the north wall to be 18' long and the West wall to be 12'. The house is slab on grade set into a sloping steep hillside. The NW corner is totally exposed, the NE corner is four to five feet deep (vertically) in the hill.



Is the floor above a heated space or unheated basement? The floor is currently uninsulated slab on grade. I'm planning to build up the floor and include a 1" dense foam layer to create a thermal break.



Insulation? Currently, none. Planning to frame walls with 2x6 and insulate to R23.



Is the ceiling on an attic or is heated space above? A heated space above, without insulation in between.



Am I over-engineering this? Is it safe to just use 15w/sq.ft. as a very rough guess? I've got a few odd spaces like this one that I need to do this for, hence the search for a DIY method.



Is there a big difference or advantage of using "hydronic" electric baseboards vs the less expensive "traditional" electric baseboards? Is there a big difference between brands? Are any of them still made in the USA?



The rest of the house is electric, and it is used seasonally so most of the time it just needs to maintain enough heat so the pipes don't freeze.



Thanks again everyone,

V

World Plumber

BTU

Rule of thumb for quick calculations.    40 BTU per SQ. FT. or  30-32 BTU/ SQ. FT. for well insulated.



MC

furthur

a couple more...

for rough numbers...

http://www.dimplex.com/customer_support/heat_loss_calculator

http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

download-able excel sheet; http://www.warmmfloors.com/heat_loss_calculation.htm

tim smith

Re: btu/sft rough #s

I would agree on the 40/sft for poor to no insulation in moderate low temp areas say design of 20 or so. The well insulated is much below what you stated. Maybe 20 btu/sft in same design temp region. Thats my take.

Tim_75

Heat losses

are pretty simply to calculate with pencil and paper. A calculator helps with the math.

Sources of heat loss are: walls, windows, ceilings, floors/perimeter and air changes.

The formula for each element is h=UAdT, where h is the heat loss, U is 1/R (more to follow), A is the area in sq. ft and dT is the temperature difference.



Air changes take a little more judgement, but basically LxWxH x HU x dT, HU for 2 exposed walls, average construction is 0.016 (1 Air Change per Hour of ACH). Except in very leaky places, like vestibules, this is not a critical load part to estimate



Perimeters can be mostly ignored except for uninsulated slab ion grade in very cold climates.



R values - are basically the value of the insulation. There are complicated ways to determine the composite R-value of an assembly and take into account surface effects and airs gaps, but practicality says R = the insulation.



Then you just "plug and chug".