Boiler sizing for radiant heat

[geotanker]

Greetings. I have a small house, that is going to need about 1600 ft of tubing for a radiant floor heat system, 3 small zones. I have a heat loss calulator spreadsheet I got online, and am trying through various sources to figure out just how many BTUHs i need in a boiler. I live in Northeast PA, and it rarely gets below 10 F in the winter. I have supplemental heat as well in the form of a wood stove, so the system doesn't have to rival the sun. I'm planning on using Propane.
Anyone have any advice?

 

[Sokoloff]

Google for the "design temp" for your location (the coldest temp "expected" in your area, not the coldest ever, but what heating systems are designed to overcome).

Then lookup manual "J" for heat loss calcs. If you want to get close with less work, slant fin (radiator maker) has a downloadable calculator program on their site. You input the design temp and a LOT of info about your house construction and it figures it out.

A lot of folks then want to go oversize (you know, "just in case") Always a mistake. If anything, undersize it a little, especially if you have supplemental heat available.

 

[IGOTWUD]

Have you considered using a coal fired boiler? You are right on the edge of the Suidi Arabia of of Anthracite coal country. EFM and Keystoker are 2 local boiler manufactures in your area. They make residential boilers from 75,000 to 250,000BTUs. I have been using a Keystoker boiler for the last 6 years, and I am verry happy with the unit. I had them add the option to burn oil, NG, or propane, (a beckett burner). I have run the unit only on coal because it is very cost effective. It does require work, loading the hopper and taking out the ash 2-3 times a week. It costs me may be less than half the cost of NG for my heat and domestic hot water.

 

[tdkkart]

According to many "experts" on this forum you cannot possibly figure this out for yourself unless you have a van with your HVAC business name on the side and have business cards that clearly state that you are a "professional". All attempts to construct a heating system without a van and business cards will result in a miserably operating system that will never work properly, if at all.
You are doing nothing but wasting time and money.

 

[hdshinn]

Give a lot of thought about using propane to fire your boiler!

We had natural gas in our last house. Not available here in our new one. Gas is gas, or so I thought. Propane is, according to my dealer, a by product of gasoline distillation and thus goes up and (rarely) down with the fluctuation of oil prices. It's way expensive here in the pacific northwest where I'm located. I'd talk to as many HVAC pros in your area as you have time for. And I'd also agree, designing this type of system is definitely not a DIY project.

I saved a little money on my system by installing the PEX tubing. My contractor loaned me the stapler to secure it to the subfloor. We used a 1 1/2" concrete (not lightwt.) fill over the tubing. How do you plan to install the tubing? Is it in a slab like this or ...? Whatever method, once it's in it should be filled and slightly pressurized until all the floor work is done to ensure its integrity to the end.

 

[badgerboiler]

You don't need a van...but it makes good sense to have a relationship with a professional contractor experienced in radiant floor heating. He has resources available to him that the layman does not.

Yes, if nothing else a professional heat load analysis performed by an experienced designer on dedicated software can save hundreds in material and days in labor.

Look for an RPA certified designer.

 

[HVAC Phil]

According to many "experts" on this forum you cannot possibly figure this out for yourself unless you have a van with your HVAC business name on the side and have business cards that clearly state that you are a "professional". All attempts to construct a heating system without a van and business cards will result in a miserably operating system that will never work properly, if at all.
You are doing nothing but wasting time and money.

You can figure it out yourself, then come back on here whining why it doesn't work properly. Ask the clown in the plumbing/heating department at home depot, i'm sure he can give his "proffesional" opinion.

 

[raspy]

Greetings. I have a small house, that is going to need about 1600 ft of tubing for a radiant floor heat system, 3 small zones. I have a heat loss calulator spreadsheet I got online, and am trying through various sources to figure out just how many BTUHs i need in a boiler. I live in Northeast PA, and it rarely gets below 10 F in the winter. I have supplemental heat as well in the form of a wood stove, so the system doesn't have to rival the sun. I'm planning on using Propane.
Anyone have any advice?

If you have a house with "normal" modern construction and insulation in a non severe area, you probably will have a design heat loss of about 7 BTU/ sq ft, or so. In this case a delivery of about 25 BTU/ sq ft gives reasonable response without being overkill. If you get a boiler that will deliver about 25 BTU/ sq ft, you will definitely be in the ball park. A non condensing propane boiler will be about 82% to 84% and a condensing boiler will be about 95% efficient.

So, if you have 1600 sq ft you would be safe with 1600 X 25 = 40,000 BTU delivery. In a non condensing boiler that would be 40,000 ÷ .82 = 47,000 BTU boiler, or rounded to 50,000 BTU.

This number can be increased by up to 50% or so for a single thermostat system with in-slab radiant, or reduced for a baseboard/low mass system that might be designed to match the load. Best comfort and economy will come from a multi-zone system with setback thermostats.

This is a rough example, but will get you in the ballpark and started down the right path.

Condensing modulating boilers can trim their burners to about 25% of full fire output. So these will come on hard in the beginning and trim to match the load while dramatically increasing their efficiency.

The next step is to work on your plumbing scheme, and this is where it gets interesting. Be careful. I've seen large companies give out schematics that would not work and, so called, experts that had no clue either.

Just for fun you could look at the Triangle Tube website and study their systems and boilers. One fine unit they produce is the Solo 110, and they have lots of info that might be a bit over designed, but very good and will work. Study the designs and understand why they included the parts they did. I find they can be simplified and still do everything well. Another source is the book "Pumping Away" by Dan Halohan. Fun to look at and understand. Do some research and ask some questions. Be wary of the "plumber" that does hydronics as a sideline and also be wary of the so called engineer or board member that wants you to be impressed with his title. Physics are physics and are not responsive to titles. Comfort and efficiency are the goals.

Hydronics is a special field that requires curiosity and some understanding of heat transfer, what characteristics water has and how it interacts with air or flows through pipes, and under what conditions people feel comfortable. That's what makes it so interesting and opens the door to creativity.

 

[Jackfre]

I'll be moving into my new, but approx 140 yr old stagecoach station house in the N CA foothills in a couple weeks. I heat it with Fujitsu mini-splits and LP Rinnai Energysavers, both companies I represent, so disclaimer acknowledged. One of my first projects is a new water line, underground power supply and an underground 1000 gallon propane tank. I will ameliorate the price spikes of the season by maintaining sufficient storage to carry me thru the season. That is not bullet proof, but I should be required to fill only once a year depending upon how long the power is out in the winter. Whatever type of delivered fuel you use, that is the way to make it pay. "Pay" is not the right way to look at it I know, but... Anyway, get all the storage you can and you will not get raped thru the winter. Own the tank and you can shop your fuel buy as you like.

What is important to you with almost any heating device is to not grossly oversize it. If you go with a modcon lp boiler, the turn down ratio should be in the area of 5:1. On modulating appliances, the low fire size is more important to you than the high fire. That point can be argued quite successfully when it is 10 below, but 99% of the time it is correct.

A Mini-split heat pump system and your radiant will give you cooling and heating on the mshp and you do not have to bring your radiant on until you have a load against it. I've had great success selling that concept. It will work for you too!