Low mass VS High Mass Boiler

Bob Sweet

Would you decifer that for us? I agree with Bob, holy crap!! But then again he may understand it.

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Dwayne in Halifax

Low Mass vs High Mass Boiler

I am replacing my antique oil fired boiler. House is OLD, 2000 sq.ft. with cast iron radiators throughout. The low mass boiler option (8 gal) is $2000 more capital cost than the high mass boiler option (25gal). The low mass is sleek European design with controls, outdoor reset etc. while the high mass is pretty standard. Why should I consider the sexy low mass option? Vendor seems unable to answer question.

Many Thanks

Brad White_189

Sexy Low Mass Option?

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Hey if it works for you...

Here are a few thoughts on mass as it relates to heating systems as I see them:

The notion of using low mass boilers to me translates into "fast response". No waiting for water and iron to come up to temperature. Fire and go.

The other aspect is cycling- boiler cycling versus steady state is a huge efficiency drag. Every time a boiler starts it's firing cycle it takes at least a minute or two to achieve stable combustion. Many times that is not reached when it shuts down waiting for the next call. The momentum is lost in a way.

Even low mass boilers (especially non-modulating types but any boiler with more output than load at a given time), will cycle. But with low mass, the losses are less, recovery is faster.

(If you are talking about a ModCon as your low mass boiler and you have natural gas available -I have to imagine this is the cost delta, not comparing cast iron to copper tube types-, that is a no-brainer. Low mass oil is not something that is in my experience but others would know.)

Now, when I come across a project where a low mass boiler has cycling issues, the solution often is to... add mass! Usually a buffer tank, into which the low mass boiler can effectively pulse bursts of hot water into a constantly circulating radiation loop.

With high mass boilers, your dominant system mass is usually in the boiler and that, absent a vent damper and good insulation, can act in part as a reverse heat exchanger which takes more time to recover...

With low mass and separate buffer, you decouple them; you may lose the small amount of mass-heat but recover it quickly rather than have your mass-loss in line with the radiation if that makes sense. Not an absolute situation for there are many ways to pipe them up. Just some brief notebook principles and not the last word by any means. You are fortunate to have cast iron radiators though. Use them well.

My $0.02

Brad

jp_2

early winter, middle spring

looks at these times a year?

when there is longer times between heat calls. needing to constantly heat that 25 gallons for smaller heat calls?

Bruce M_2

Low Vs High

It would be helpful if you mentioned the specific make and models of the two boilers. You need to look at the life cycle theory of costs and not the immediate cost of a boiler.

Bob Bona_4

I have

nothing to add, but holy crap, Brad.

LMAO!

Dave Holdorf_2

Low mass and high mass

You have almost the already perfect high mass heat emitter in the house to work with a low mass boiler.

With the cast iron radiators and a low mass (modulating condensing) boiler, you can a much more efficient and comfortable heating system. The radiators are probably oversized a bit (your comment of OLD house) and therefor can benefit from a modcon by not having to go to 180 degrees all the time. You can take advantage of longer run times of the boiler with lower water temps and also add outdoor mixing valve control for the best performance and comfort available.

Dwayne in Halifax

Sexy low mass vs less costly high mass

I have decided in favour of the low mass (probably a BIASI H10 or De Deitrich 126A) over the high mass option. The Biasi and De Deitrich are both nice boilers, with a 3pass heat exchanger and they are both low mass oil fired units that can be converted to GAS if when the opportunity presents itself. STill no gas in my neighborhood.

The high mass system I was looking at was a Saturn 5 by KERR which is a locally made "Pin Type" boiler with an integral coil for Domestic Hot water. It is at least $2000 cheaper but the technology is OLD.

I hope I am making the right decision in the long run. Before I put my $ down I feel obliged to find someone from Latin America to help me with Brads e-mail.

Thanks for your insights all.