In Floor Heat – Boiler – Help

We have in-floor heat run by a boiler. On natural gas. Love the in-floor heat, very even and warm in our walk out basement…. doesn’t feel like a basement at all.

We have a 16 yr old Dunkirk boiler and according to my Heating guy the heat exchanger is bad and the whole boiler needs to be replaced. He says that the aluminum parts make it fail sooner than it should. This is a condensing boiler.

He suggests replacing with a Weil-McClain boiler, which is non-condensing and has cast iron parts.

Does anyone have any knowledge or opinions on the situation? Or questions I should ask? Anything else I should think of or know before going ahead and replacing?

Is there a warranty on the heat exchanger through the manufacture?

The non condensing boiler may need to be piped differently to prevent condensation on the cast heat exchanger. That and it will cost more to operate because a non condensing boiler is less efficient.

Coletrain27 wrote:

Is there a warranty on the heat exchanger through the manufacture?

10 yrs on the Dunkirk heat exchanger I believe.

Dave maze wrote:

The non condensing boiler may need to be piped differently to prevent condensation on the cast heat exchanger. That and it will cost more to operate because a non condensing boiler is less efficient.

He was explaining that the venting would need to be changed from PVC to stainless or aluminum; it’s vented out the side of our house.

Generally, a condensing boiler is more desirable then due to higher efficiency?

Yes, they are more desirable because of efficiency. They are also easier to vent because you can use pvc, and the boiler piping is less complicated.

19 years going strong with my Well Mclain Boiler and In floor heat throughout the house and garage.

Curious what parts failed…
Also, what is the typical return water temperature on your in-floor loop?

He’s right the non condensing boiler with cast iron is more durable but they are generally used in baseboard heat with higher water temps and might have issues with lower temps used with plastic/pex tubing. We used to install electric boilers from electro industries in monticello that were bulletproof but your costs will go up. I’m sure the newest condensing boilers have made improvements and will work better with your system. All manufacturers reverse engineer their products and 15 years is what they shoot for to stay in business. I would go with a good brand and not overcomplicate it…my two cents.

The lifespan of most condensing boilers is about 15 years and they run up to 99% efficiency. the lifespan of a non-condensing boiler is about 30 years and they run less than 80% efficiency, which is why you can’t have PVC venting, the exhaust gasses get too hot.

IMO the cost of gas is unlikely to go down, and if your previous boiler ran fine for the majority of its life I’d stick with what you had.

A second opinion may be a good idea as well.

A non condensing Boiler in your situation does not really make much sense. In order to run a non condensing Boiler at low temps you will need to add some sort of mixing device to lower the supply temp to the floor and allow the boiler to run at a high enough temp to not condense. Any time a non condensing Boiler runs with a return water temp below 135-140 degrees it will condense and destroy itself over time. I’ve seen boilers that were completely rusted out after just a few years running like this. The cost of replacing the venting and adding either a mixing valve or doing injection mixing will probably be about the same as the cost difference between a non vs condensing Boiler. Combine that with efficiency over the life of the boiler and ability to use outdoor reset to control the supply temperature will shift the balance even further. There are many new condensing boilers with stainless steel heat exchangers available today that are Rock solid units. I am a master steam and hot water installer and master plumber, feel free to pm me if you would like.

John Miller wrote:

A non condensing Boiler in your situation does not really make much sense. In order to run a non condensing Boiler at low temps you will need to add some sort of mixing device to lower the supply temp to the floor and allow the boiler to run at a high enough temp to not condense. Any time a non condensing Boiler runs with a return water temp below 135-140 degrees it will condense and destroy itself over time. I’ve seen boilers that were completely rusted out after just a few years running like this. The cost of replacing the venting and adding either a mixing valve or doing injection mixing will probably be about the same as the cost difference between a non vs condensing Boiler. Combine that with efficiency over the life of the boiler and ability to use outdoor reset to control the supply temperature will shift the balance even further. There are many new condensing boilers with stainless steel heat exchangers available today that are Rock solid units. I am a master steam and hot water installer and master plumber, feel free to pm me if you would like.

X2

What John Miller said , he nailed it .

Thanks very much guys. That makes sense and I’d prefer the higher efficiency that we’ve been used to. Not to mention it is pex tubing and I don’t want it to get too hot or cause any problems so sticking with the same type of system seems like the best idea.

I like this heating guy, and he is a small outfit and seems very honest. But I don’t think he works on boilers all that often.

John I will probably PM you a couple more questions thank you

We had a Well Mclain Boiler at home with hot water baseboard heat. Dad installed it as he was a self employed plumber. I was a young man then and it was still going when we sold the housesome 40 years later.

I have two Triangle Tube Condensing Boilers with stainless steel heat exchangers.
One in my house that supplies heat and hot water for 2400 sqft and two bathrooms and four separate heating zones, and the other supplies heat for a 800 sqft shop building.

The shop unit I installed myself, had the pex tube put into the floor when the building was built.

Replacing a boiler with one of the same type is a pretty simple task. If you can solder copper tube.

I have Navien’s in both my personal shop and business shop. They have only been in for about three years, but work well and were the overwhelming consensus from the plumbers I talked to.

If it is for only supplemental heat, a water heater listed for space heating is a good choice. Simple, reliable and much less money than a boiler.