Condensing Gas Boiler or Non Condensing?

curiousman

I've decided to switch from oil to gas and I'm thinking of going with a Viessmann condensing boiler. I've read many pros and cons regarding condensing boilers. If I go with a non condensing boiler I'm going to go with the one my installer knows best because I think many of those brands are basically the same.

psb75

The other part of your heating system--the part that radiates the heat is critical to evaluate if you want to get a condensing boiler. Viessmann makes some 'top notch' equipment. But...it won't condense if you don't have the right set-up. It would be a shame to spend that money on VIessmann and not have it perform to its full potential--or any other condensing boiler for that matter.

Jamie Hall

As @psb75 states, for a condensing boiler to be of any value, it must be able to condense... which sounds, perhaps, obvious -- but it isn't the boiler which controls that, it's the radiation in the structure.

You need to determine what temperature water the radiation in the house can run at an satisfy the heating requirements of the house. Many -- if not most -- older structures were built with radiation intended to use water in the 160 F to 18 F range. If that is the case in your situation, the boiler won't condense and you'll be far better off with a conventional boiler.

In any case go with a boiler which your installer knows and likes and will service. The most efficient advanced spectacular boiler in the world is simply an expensive piece of junk if the installer doesn't know how to install and service it.

hot_rod

A heat load calc and heat emitters inventory would be the best first steps. Next, look at options for reducing the load with some insulation or air sealing. Then you can determine operating temperatures required.  Even on higher temperature systems, you may only be at those design conditions for a small part of the year. So it is possible to run condensing mode if the boiler is set up on an outdoor reset control. 

The modulation function of a mod con boiler is also a great feature to reduce cycling 

psb75

Good point hot rod. The class of boilers under discussion are generally referred to as "modulating AND condensing"! Double bonus.

SuperTech

I would only recommend a condensing boiler for low temperature radiant heating, or if you are planning on selling the house within ten years. Baseboard or radiators and planning on staying in the house long term I would go with a Weil McLain or Peerless for a basic cast iron boiler, they typically last longer than a Burnham.  If you want a high quality non condensing boiler I would look into options from Energy Kinetics.

Hot_water_fan

hot rod is right of course, determining the heat load and comparing to your installed radiation is key. If you have the oil receipts handy, it'll be easy. It's important to realize that you'll only need the high temperature water a fraction of the year, so you'll be saving the other 90% (or whatever) of the heating season.

Steamhead

SuperTech said:

I would only recommend a condensing boiler for low temperature radiant heating, or if you are planning on selling the house within ten years. Baseboard or radiators and planning on staying in the house long term I would go with a Weil McLain or Peerless for a basic cast iron boiler, they typically last longer than a Burnham.  If you want a high quality non condensing boiler I would look into options from Energy Kinetics.

This.

What seems to get lost in this debate is the extra maintenance condensing boilers require, and their shorter lifespan. Also, there is no such thing as parts standardization with condensing boilers, so everything has to come from the manufacturer. It's not possible for a contractor or supply house to stock everything for every condensing boiler, whereas, for example, if the gas valve on a standard cast-iron boiler needs replacing, in almost all cases a standard part can be used.

I don't like to be the guy who has to tell the owner no one has the part he needs and it'll take two weeks to arrive. I think that's ridiculous, and my customers would agree.

curiousman

I had a guy at the house recently to give an estimate and he said I have to change the half inch piping to three quarter inch that goes from the boiler to the radiators. He also said I'd have to change at least five of the old radiators as well in order to do the job to his satisfaction. He said he would not do the job unless I did those things. According to him no matter what kind of heating system I choose to install, any new boiler would not work to the optimal level without doing those changes. Looks like it's going to be a lot more costly of a project than I expected.

Jamie Hall

I think you may need a different contractor...

curiousman

I'm getting other estimates so I'll be interested to hear what they have to say. It would be great if I didn't have to change the piping, however the house is 67 years old with five of the old style radiators that were installed when the house was built so I'm almost certain those should be replaced.

Zman

Before making the decision on upsizing the pipe, you need to look at the approx distance of the pipe and the number of heaters served. There is nothing inherently wrong with 1/2" pipe in a heating system. How does it heat now?

curiousman

My current heating system is a 1954 American Standard oil boiler. It has always worked great in terms of heat.

Zman

What type of radiators do you have?

Jamie Hall

Absolutely no reason to replace the radiators. Unless they get frozen and crack, they don't wear out.

curiousman

Here's a photo of the old radiators. Five in the house are like this and the others are typical baseboard that are also old.

curiousman

I meant to say a photo of what they look like. I pulled that off the web,

curiousman

The others in the house look like this.

JakeCK

Get a second opinion and make sure s/he does the math. He sounds like he's holding his wet finger up in the air and using rules of thumb.

pecmsg

Slant fin makes a user friendly heat loss calculator. 

Zman

If you are getting good flow and distribution now, there is no reason to change that part of the system.

rick in Alaska

curiousman said:

I had a guy at the house recently to give an estimate and he said I have to change the half inch piping to three quarter inch that goes from the boiler to the radiators. He also said I'd have to change at least five of the old radiators as well in order to do the job to his satisfaction. He said he would not do the job unless I did those things. According to him no matter what kind of heating system I choose to install, any new boiler would not work to the optimal level without doing those changes. Looks like it's going to be a lot more costly of a project than I expected.

1/2 inch pipe can generally do about 15,000 btu's, so most likely it is fine. You would just need to see what kind of load is on it to determine that. I would say if your heating system is working now, then it is fine.
Why does he want to change the radiators?
Sounds like you need to do some more shopping for a new contractor.
Rick

curiousman

He said the older radiators(like the first one I posted) should be replaced. I think it has to do with lack of efficiency? I've had other people tell me I don't have to replace them and others said I should.

curiousman

The Viessmann Vitocrossal 300 is something I'm considering. I'll be getting an estimate from a local guy who came highly recommended.

Zman

curiousman said:

He said the older radiators(like the first one I posted) should be replaced. I think it has to do with lack of efficiency? I've had other people tell me I don't have to replace them and others said I should.

There have been very few improvements in radiator efficiency in the last 80 years or so. Unless he is pitching the idea that you can run lower water temps by upgrading the radiators to larger ones, I don't understand why he recommends an upgrade. It would be a good idea to vacuum any dust out of the radiators.

Jersey2

curiousman I am planning to do the same thing, switch from oil to gas. Are you in NJ? I wouldn't dream of replacing my cast iron baseboard radiators. My current antique can easily heat the house to 90 degrees in the winter if one was to put the mercury filled thermostat to 90. Mine has 1" copper with 1/2" tees and 1/2 copper that goes to the radiators. I don't plan on getting a high efficiency boiler, the heating system isn't very long in NJ.

curiousman

Hi Jersey, I'm in MA and also have half inch piping. My old 1954 American Standard oil boiler stills heats my house fast in the coldest days. You might be better off going with a conventional boiler. I keep going back and forth because many people don't think the condensing boilers are with it.

Zman

I have found that properly installed and tuned fire tube modcons do not require more maintenance and repairs than atmospheric boilers. They will also save energy, how much depends on how low you can go on the outdoor reset.
The vast majority of modcon boiler issues on this site are the result of incorrect sizing, incorrect installation and/or a lack of proper combustion analysis and tuning.

psb75

Well said Zman.
Nothing to add.