Hi all,

I'm in PA and removed the old oil fired boiler in my house- no idea what BTU it was.

I need to size the new natural gas fired boiler to the house and have to do a heatloss analysis. But, while knowing the principle of how to do it, I'd like to have a simple method for doing a heatloss calc.

Can you folks recommend a reliable method to help determine a new boiler size?

Thanks,

Craig L.

 

Hi Craig,
Heat loss numbers will vary all over the place depending upon size, insulation, air leakage, windows, basement, and location (and more). There are no reliable wild guesses and even if you knew what size the old boiler was, it was probably way too big.

Besides replacing the boiler, will you or have you upgraded any of the energy issues above?

There are programs you can use to do a good job of pinning down that number, but if you are not into that level of detail start by adding up the existing baseboard radiation. But, all of the above is important, especially if you will be living there.

Bud

 

Bud, I already understood all of that.

I'm looking for a program to do a heat loss analysis. Looking at Manual J right now.

 

We never know how far each homeowner is going to get into their decision making progress. A full calculation is good.
Wrightsoft hvac software is the one I see most frequently mentioned. I haven't used it as my energy auditing work looks at heat loss a bit differently. Similar results, but mine doesn't size the hvac equipment on a room by room basis.

Have you looked at that software?

Bud

 

Bud,

Yes, I just looked at "Right J" on Wrightsoftware. Looks good but the price is prohibitive.

There has got to be an easier way.

Craig L.

 

They used to offer a single use option for something like $50 or $75 but I could not find it. While I look maybe some of the hvac pros know if that is still available.

Bud

 

Still no luck finding the single use Writesoft. But, much of what it does can be accomplished with this one.
Home Heat Loss Calculator
With gas, pinning the heat loss down to the last BTU isn't all that important when a furnace can cover a reasonable range.

Take a look at the builditsolar calculator, I have used it often to judge where homeowners can best spend their energy improvement money and I can help with some of the input data.

Bud

 

I'm going to be using a boiler, not a furnace.

I'll give the builditsolar a try and let you know how it goes.


Craig

 

Just tried the Heatloss Calculator here- Home Heat Loss Calculator

The result I got was close to what I had estimated. Except, the result was about 10k Btu lower than I expected. So, some of the input areas were adjusted for a colder and more lossy house. The result was still acceptable.

I find it odd that in most of these heat loss calculators the designers of the software assume that everyone lives on a slab foundation with no basement.

 

If you have an unheated basement or crawlspace any heat that goes through the floor must then escape through the foundation. For heat loss in that direction I use an estimated r-value for the exposed foundation area plus one foot below grade. If blocks I use 2 feet below grade.

But you are correct, although basements are difficult to model they shouldn't be left out.

Glad your numbers are close. With a modern boiler you can use controls that vary the circulation temperature depending upon outside temp. But I'm getting out of my knowledge base as Maine does not allow energy auditors to do ANY hvac work.

Just curious, but what was your resulting heat loss?

Bud

 

Bud,

Here's how I did the rough....really rough estimate; 25 x SF or, 25 x 2500= 62,500 Btu

Using the Heat Loss Calculator the figure was about 64,000 Btu.

The new system will have 6 zones.

Any opinion on the size of the boiler relative to the amount of zones?

 

Again, I'm not a hvac pro, but IMO multiple zones reduces the load on the boiler size. Based upon your design temp the size of the boiler is supposed to be able to maintain the house temp by running continuously. But, in reality all stats are probably not set to 70 degrees or are not all calling for heat at the same time. And if you run into a really long stretch of cold weather well below the design then simply set a few of the zones to 65°. 65° vs 70° is a 19% reduction in heat loss. So anything in the range you calculated would be fine.

My gut feeling is that 6 zones is a bit too many as some may end up being very small, thus resulting in more frequent short runs for the boiler. Just my opinion.

Then, there are probably a few areas where you can make some energy improvements. Basements are often an area where air sealing and additional foundation insulation can help. But I know nothing about your home.

The heat loss calculation you used gives you the loss per defined area, ceiling, walls and such. That is where I use it to identify the best targets for improvements.

Your next search will be (maybe already done) finding a local service company. But you sound like a capable DIYer.

Best,
Bud

 

There's a sticky at the top of the forum page with links to a couple of heat loss programs. Steve

 

Steve,

I saw them but most are dead links.

 

Bud,

I added a little extra loss to the overall analysis to get a higher figure. The intention in the future is to connect a "side arm" to the boiler for domestic hot water...maybe.

Too many zones is a possibility but I want to be able to effectively isolate various portions of the house and can always combine them into a lesser number. In truth, I love to work with this sort of stuff.

I'll be doing the installation work. 'Have already installed/replaced 3 boilers and 6 hot water heaters. At my age this will be my "magnum opus" and last boiler installation in my lifetime.

Please pass along any other ideas you may have if it's convenient for you.

Thanks,

Craig

P.S. Another complaint I have about heat loss calculations is that none that I've seen mention exterior stone walls with framed interior as an option. Brick, yes. Stone, no.

 

Brick vs stone? Their r-value is so low that any difference between them would be lost when they are included with another insulated assembly. Example, the listed r-value for an 8" block wall is only 1.1 for the entire 8 inches. Plain bricks, similar to stone, are listed to range between 0.1 and 0.2 per inch. Thermal mass, yes, but insulation value, no.

An indirect hot water heater on its own zone is considered the most cost effective for generating hot water. However, that depends upon how much hot water the household uses. Under very low use, an electric water heater would allow the boiler to shut down the entire summer and it could be far less expensive to install.

I see you have listed Maine in your profile, are you abandoning us, LOL. I worked hard to get back to Maine and have no desire to leave.

Bud

 

Maine? No, I'm in PA. I'm just sick and tired of all the questions you have to answer just to sign up for mostly anything on the i-nets. "We want your soul", etc.

Data is the new "oil" of the 21rst century.

But, this is a very, very good forum and I'm thankful for it.

Thanks for the information about stone. Thermal mass is so true. We have what I call "the 3 day rule". It means this- when the temperature drops below 50° F then we have about 3 days before I have to start using firewood to heat the house.

Oh, here's a nice to know- the degree symbol- ° is made by holding down the keys- Control, Shift and then tapping the letter "u". Then release all of the keys and hit the following numbers- 00b0. That's zero, zero, b, zero.

Pretty neat.

 

Hold ALT plus 248 = °
Pull up one of the ASCII lists, many will work here.
So ME is your disinformation, we all need to do more of that to make their data gathering worthless.

As for the forum, as you spend more time here you discover who is who in each category. Some really knowledgeable volunteers here.

Bud

 

Thanks Bud. I'm working off of unicode and Linux so the Alt doesn't work.

Well, for privacy the bottom line is IP address. Everything else is cute and fine but of no real value to data miners and sellers.

Thanks for all the help. Big day tomorrow. I'm going to order the boiler. I hope it'$ not too expen$ive. Got a "quote" (blood letting) from one of those typical "do you have an account with us" plumbing supply houses of about $1,500. Not bad. Can't buy it Delaware because they want to be sure you're A LICENSED BY GOD PLUMBER.

The boiler will be a US Boiler (Burnham) Series 2 model 204. 96k Btu input and 70k Btu net...about.

Here it is- https://file.ac/ZYgLWyMdFsk/Series%2...ta%20Sheet.pdf

Craig

 

70 / 96 = 73% efficiency. Hmm.

 

Let me look.. I posted those links..

2500 square ft is your home?

What type of heat emitters?

How many feet total roughly of element each zone?

 

Did you try the i phone download? That one works..

yes is your home is insulated on average with no real drafty old windows use the 25x sq ft..

I used the original slant fin calc on my home and it came to the same as sq ft x 25..

Remember the boiler you buy goes by DOE, not IBR..

Also the is a 20% fudge factor of being oversized when you buy a new boiler..

 

Lochinvar 2 stage units are nice.. You can get at Avco supply right in PA. ( Tell Rich I said hi..LOL)

CBN090M-9 - Lochinvar CBN090M-9 - 65,000 BTU Output Two Stage Spark Ignition Solution Boiler (Nat Gas)

But these have copper heat exchangers... But two stage gas valve I like..

 

No, 82.3% according to US Boiler.

 

actually 80K DOE..


Probably way oversized... But going from oil to gas should save a buck or two...

 

I'm not a iPhoner.

I don't understand what you're talking about. It's too vague and disjointed.

Never heard of Lochinvar and wouldn't buy from SupplyHouse.com if you paid me. Called them last week and asked about the installation of a flow check valve and they gave me the "you'll have to call a licensed plumber" routine. 'Sick of that nonsense.

Yes, might be oversized but we're also planning on an addition of the house.

 

Yeah whatever... Avco supply is in PA...I only linked supply house as a reference..

You never stated what heat emitters or how many feet...

No matter... You seemed to have answered your own question on what your buying so why ask anything more here......

 

I found a really easy heat loss calculator. It costs $39 for a 60 day use and then it expires.

I bought it and used it. The results were within a few thousand Btus of the Solar heat loss calculator mentioned earlier in this post.

Here's the link- How to properly size a residential hot water boiler and radiators

 

yup and probably right on line with the 25x sf you got... You could of saved 39 bucks

 

An accurate way to find boiler size is to collect operation data on the existing one, which in this case is no longer possible. If your old one still runs try this.

For a period of time, say a week or more log degree days, gallons oil used and burner run time usinng a clocks/hour meter” Find efficiency boiler using using measured stack temperture and efficiency chart. Most charts use “net” temp so deduct room temperture from measured reading.

Measure oil pressure on burner. Use Delavan or other chart to get actual nozzle GPH at that pressure.

Calculate BTU/Hour: 140,000 BTU/Gal X Actual Nozzle GPH X Efficiency (use 80% if unknown) = XXXXX BTU/Hour

From logged data for period divide degree days by hours run for DD/Hour.

Find Design temp load at 0F (65 DD's) by dividing by DD/Hour to get hours run/day at 0F. For example if result is 8 hours run out of 24 then actual load is 33% of current boiler XXXXX BTU/Hour.

When domestic hot water is part of load then an adjustment for it should be factored in. My house uses 1 gal/week in summer for DHW with an oil fired round water heater.

This same data can be used to raise boiler efficiency by cutting nozzle size while still insuring accurate heat on design temp days.

Run time hours is also a good way to find central air conditioner load. Clock a few hours during mid day period when temperature is relatively stable, say 95F. The percentage of time per hour run X AC Rated BTU/hour = BTU Hour.

 

The old boiler is long gone.

I've now installed a new boiler, or rather I'm still in progress on it. It has 6 zones but only 2 have been finished so far. So far....so good.

I'm using PEX 3/4" oxygen barrier tubing. PEX really makes the entire process easy. Got all of the material from PexUniverse.com. They were the lowest priced anywhere.

By way of background, I've heated with wood for 30 years but realized I'm getting too old for that method. You can't imagine how nice it feels to set the thermostat and in a few minutes feel warm!

 

Hi Craig,

I'm in PA also and went through this same exercise only a few years ago. What you did as a rough is PERFECT - 25 x SQ FT or 62500. So - a pretty much ideal choice is something like a 70,000 BTU boiler at 80-85% efficiency.

Supply.com is awesome (used to be supplyhouse.com). I've gotten a ton of stuff from them and plumbed my entire house from scratch. I did buy the boiler and indirect from a local supply house though - and they were helpful to ensure that I also got the appropriate expansion tank, various valves, etc.

You really do NOT want to size it larger than this, as your boiler will be over-sized and will short cycle. It's best for it to run LONGER at a lower capacity. Even if you have an indirect water heater (as I do) you should NOT size the boiler any larger due to this. The indirect will simply be on a priority circuit (either in the boiler itself or a priority circuit in the pump circuit controls). Some contractors think (erroneously) that the indirect water heater is added to the total heat loss calculation - and this is totally incorrect. It will simply be on a priority and take only 10-15 min (at most) to satisfy. Burnham has a really nice indirect 50 gallon.

A BIG thing is to install a bypass right next to the boiler, so you can mix the outbound hot with the inbound return - to warm up the return water before it hits the boiler. Use the same size copper pipe (probably 3/4 ") for the bypass as the size of your supply and return lines - and install a shutoff ball valve in the middle so you can easily modulate the mix. Boilers vary a bit but if you can modulate the return water to about 130 F that should be about perfect. Some boilers can tolerate a lower return temp than this.