Heat loss

Brad White_25

That brings your heat loss per SF (check figure only) to 32.5 BTUH. That seems a LOT better, more in line with what I would expect for modern construction that is well insulated.

I would still double-check your take-offs, glass measurements and such but you can see how much safer you will be now.

Another check or triangulation is to assess what your current radiation output is at a certain temperature. (Say it is baseboard and may run at 170 AWT. It may have an output of 450 to 600 BTUH per linear foot. Just an example).

Point I am trying to make is, say your total radiation output at it's orginal design works out to be, oh, 60,000 BTUH. There is then no point in putting in a boiler with a heating capacity greater than the radiation (unless you are making DHW and sizing is close). But the idea of having a heating-only boiler that does not have the connected radiation to dissipate that heat into the house is a waste.

Again, just a cross-check to corroborate your heat loss calculations.

Let me know what else you may need, OK? Sorry not to get back right away; I was away from home.

Best,
Brad

Mark_46

29,300 BTU loss

Does 29,300 BTUs/hr heat loss sound bad for 1,573 sq ft of heated space? What is typical. Portions of my house are not insulated, I know it's bad but how bad?

Brad White_24

Depends on where the house is located

What is your design outdoor temperature?

Your house is approximately the size of mine and has about half the loss. I am in Boston with a 6 degree design temperature and an older house insulated as well as I could. I would kill to have that low a heat loss.

If you are in Baltimore or Richmond you may be more in range.

If you live in Florida it would be high.

If you live in Alaska, gee, it must be dark in there with no windows, below ground and with seven huskies in your bed...

Mark_46

Can you tell me how to calculate design outdoor temp? Otherwise, I dont have that number.

I am located in the very Northeastern portion of New Jersey.

If my losses look that good, i may have made errors in the calculations. I am using the Slant/Finn software linked on this site.

Unknown

That's about 18 BTUs/sq ft... pretty average in most cases. In milder climates people often use less insulation so the heating intensity range stays pretty average unless you're in a very cold or very warm area.

Brad White_24

Mark, what city is closest to you?

I have posted data for Teterboro AP, also Mcguire AFB near Trenton which I have used for design work at Princeton and Lakehurst for comparison.

I am guessing Teterboro is closest to you. Winter design at Teterboro 99.6 percent occurance is nine degrees F. The median of extreme lows is 2 degrees by comparison. That is not a design value, just informational. I would use 9 degrees F.

Only if your house is new and built to the best envelope standards, with excellent Low-E glass, air barriers and R-19 wall insulation, R-38 roof insulation would I consider your calculated heat loss to be borderline appropriate if not a tad low.

Air infiltration is the biggest wild-card and heat loss contributor. Are you sure all factors (walls, glass, doors, roof, perimeter, basement, infiltration) have been accounted for? Naturally glass type and area can affect the total greatly also. Remember too that the best envelope components degrade over time. Settling, wind loads, water penetration and age will affect how tight the walls, doors and windows can be. The start out great and go down for there. I tend to design for a 15 year-old home. In other words add some safety factors (10% is common) to account for these unknowns.

As general "check figures" (not for design purposes), I expect to see the best of today's homes in your climate in the 22-26 BTU per SF range. Older homes with upgraded insulation and envelopes 30 to 40 BTU's per SF and an uninsulated older home in the 50 to 60 range as points of comparison. Anything much above or below triggers an audit of the calculation inputs, for me.



My $0.02,

Brad

Mark_46

Brad,

Great info thanks. Yes, Teteboro is closest of those you listed, about 10 miles away.

Yes, my house isnt even close to those insulation standards you listed. The house was built in 1924 and I am fairly certain which parts of the house are not insulated. I accounted for those in the software. But i would think the house should fall into that 50-60 BTU per SF range knowing what I know about the house.

I chose the most appropriate descriptions from the drop down menus in the software. They dont always describe perfectly. I did not include the basement as it isnt heated. The window area values were not accounted for as the software does not allow. Maybe it can, I must take a closer look.

If I can ask, once you have the Heat Loss number, is that what the BTU rating of the boiler should be? Or is there another formula from there?

Brad White_24

Your House

The house I am in process of renovating now is similar to yours, Mark. The one I referenced is my current home (built in 1873) and the current one was built in 1928 or so.

Firstly, insulate the house as much as you can. It will pay dividends short term in comfort, long term in energy. Dense-Pack cellulose is a good place to start, but ask around. Imagine lowering your heat loss (and boiler size right off the bat) by 20% or so. Maybe more.

If you do not include your basement because it is not heated, then you have to take into account the floor and heat loss to the basement which might be 20 degrees or more colder than the occupied house. This could be over 6 BTU's per square foot right there, if the floor is not insulated. You can knock that down by 80%+ if you put in R-19 insulation.

Not familiar with the software or why there are few options on the glass.

Here are some sample U-factors (multiplied by area and temperature difference indoor to outdoor):

Single-pane glass: 1.04 to 1.13
Single-pane glass with storm windows: 0.65 to 0.70
Double-Pane Low-E: 0.35 to 0.45 average. (Center of glass numbers are always lower but are not accurate for calculations).

Uninsulated Frame Wall: 0.28 to 0.35
Insulated (Blown-In) Existing Wall: 0.09 to 0.15 (Framing has an impact).

Uninsulated Floor: 0.30 to 0.35 if with a plaster ceiling below. 0.50 or more if just wood floor and sub-floor on joists, exposed below.

Point is you should be very sure all aspects are taken into account. But do NOT give up and use a "per square foot" value. Take your time and do it right. I just may be able to review your calculations if you like, if you contact me off-line. Just a sanity check if nothing else.

Hope this helps!

Mark_46

Brad,
Thanks again.

It may help to contact you off line. How would I do that?

Brad White_24

Contact:

I scramble my e-mail address, Mark, to foil spammers.

But for you only, just between you and me it is:

bewhite (at) rcn.com

Mark_46

Brad,

I think I found my error...or should I say you found it.

In this software I'm using, you must first enter Job information before entering any room-by-room data. In those fields I first entered:

Indoor temp = 70
Outdoor temp = 35
Altitude = 100
System design water temp = 176

The assumptions I made were 70 degrees desired indoor temp, 35 degrees average winter ambient temp for my area (i guess that was the big error), 100 ft alt. and system design temp is the max temp output of the munchkin boiler I'm considering. (not sure if thats the right value to be using either)

Did not realize the outdoor temp value should be the value for a given geographical area according to the Hydronic Institute divison of GAMA!! The value you provided (9) is now what I entered and the results are quite different. My inputs are now:

Indoor temp = 70
Outdoor temp = 9
Altitude = 10
System design water temp = 176

My Heat loss BTU/hr is now 51,100. Your thoughts?

edlav

baseboard

i am trying to figure out how many feet of base board heat to install in each room of my house i do not have a good heat loss calculator,out door design temp live in providence

Mark_46

Sizing

Brad,

Thanks again. Not getting back to me right away is quite alright, you of course have no obligation and your information is invaluable. I was going to email my last response to you because i wasnt sure you were aware of it. There are so many postings that it quickly gets pushed down the list.

I'm a little surprised to read that 32.5 BTUH is what you would expect from a well insulated house? I know a good portion of my house isnt insulated and would expect a 52,000 BTU heat loss to be considered high. But at any rate its kind of good news!

As I continue to research all the ins and outs of replacing our system, choosing a type, sizing it, produts available, etc I learn more and more. We are now starting to 'collect' estimates from local contractors. As expected, this tends to make the question list even longer. I feel that if I brought in 10 contractors, I would get 10 different solutions.

For our application, I'm thinking 1) a miniduct air handler system is the way to go. 2) We split the house into two zones, separate air handlers for first and second floors. 3) We have two small AC condensors (1.5 ton second floor and 2.5 ton first floor) for each handler. 4) each handler gets a hot water coil fed by a boiler.

We have a estimate in hand that is just that. I feel the contractor is solid. I got the feeling he knew his systems. We got his name from Unico.

But heres my $64 question for now. Knowing I have about 52,000 BTUH loss they have recommended the Munchkin (which I like and hear good things about) 80,000 BTU %92 AFUE. It sounds a little small. I have not spoke to them about their heat loss calculations yet. I certainly understand what your saying about the boiler must be matched to the connected load, etc. But I dont know how to convert my heat loss measurements and square footage into the correct size boiler. You speak of radiation output at a certain temp. But Im not sure how to measure this. Similarly, are the heat coils in the Unico air handler sufficient? Is a 80,000 BTU boiler sufficient? Is there a rough rule of thumb that says doubling your heat loss is the boiler size needed? In my case 104,000? See what I'm driving at?

Finally, if I add insulation and signifiacantly change the heat loss of the house, then what is the correct size boiler?

Mark_46

Slant Finn

I am using Slant/Finn. Free. The linkis on this site form the home page.

Brad White_9

Mark-

Brad White_9

Mark-Sizing

Mark, I had to re-post this to keep it from going vertical!

Short answer is, if your heat loss is in the 52,000 BTUH range, the 80M Munckin would be ideal. No, you do not double anything. You want the boiler output to match your heat loss as close as possible. The 50M or 50T would be too small. Those are the breaks.

But as a footnote, if you are using the Munckin to make domestic hot water (and you should), you have plenty of reserve capacity. Not that you need it, many designers/installers do not add capacity for domestic, but it does give you a bigger engine to drive the heater when it calls. This means a faster return to heating duty and a shower that will not end.

What is GREAT about the current technology is modulation. Not on/off control, but the equivalent of boiling water on the stove then setting it to a simmer. That kind of control. In short, the boiler becomes the boiler you need at most any given time. And at low fire, all that surface area has lots of time to absorb the fuel output into the water.

If your radiation (coils, what have you, call them "emitters") can support a larger heat loss, great- it runs at a lower temperature and this is where a condensing boiler like the Munchkin thrives.

Please re-post or e-mail me directly if you need more. My neck hurts from reading your last posting


Brad

Mitch_4

Its interesting that

you find 52000 heat loss high, but a 80,000 boiler too small. It is interesting that the prevailing preconception of bigger must be better is still firmly rooted in the public psyche. (no slight intended to you)

You want an appliance that closely matches the heatloss, with out being smaller, and a bit of cushion for those days where it gets below your design temp.

Search for the highway mileage / city milage thread that was here not too long ago, it explains well how a long burn is better than several short ones to heat your house.

Good luck.

Mitch

Mark_46

No assumptions

Mitch,

I assume 52,000 is high because I know most of my home is not insulated (existing condition from build in 1924) and dont know what a typical house heat loss is. I also know fist hand our house is a little drafty or chilly.

I wasnt questioning if an 80,000 BTU boiler is too small but rather if it is right-sized. It sounded'small to me as someone who doesnt size HVAC systems everyday...wasn't sure. I agree with you, the bigger is better thinking is non-sense.

Thanks for your post though. The more input the better! :-).