Boiler Sizing?

MikeB

As part of a planned upstairs remodeling (master suite) we also intend to revamp our hot water heating system (high efficiency boiler, some new radiators, outdoor reset control, maybe zoning, etc.). I am in favor of spending the money up front for energy efficiency and improved comfort. One very tempting option is adding indirect domestic hot water. I am not at all in the HVAC industry but am an engineer who understands energy, heat, control systems, etc.. I have noticed that the advice regarding boiler sizing emphasizes “right-sizing” – especially “do not spec an oversized boiler” as it will short cycle. I understand the reduced efficiency and boiler life impacts of that. I will definitely use a contractor that will perform the heat load calculation rather than just reading the nameplate of our 26 year old Weil-McClain.

We live in Wisconsin and I assume the new boiler will be sized for a cold weekend day when we will want to heat the whole house. While it appears that this kind of thing is successfully done on a regular basis, it seems to me like zone control and/or indirect domestic hot water (especially during summer) would result in the boiler being underused or short cycling quite a bit of the time. Can someone please explain to me why this is still a good idea? Thanks.

dconnors

alot depends on the fuel choice

If you are using gas as your fuel, i would recommend modulating condensing gas.

MikeB

OK, which ones are best?

Yup, forgot to mention it's natural gas. Now I see "modulating" as a distinction among the various models.
I suppose this can open a firestorm - who makes the best?
I see Buderus (is only the wall-mount modulating?), Munchkin, Weil-McClain, Vitodens (guessing Dave will recommend Buderus). Any others to consider? Who has best history, control options, value (quality and performance per dollar)?
Are there any brands or models I should just plain stay away from in terms of quality, difficulty of service, too new (I never buy a car in the model's 1st or 2nd year of production), etc. ? Might be an area of strong opinions - please be civil. :-)
Thanks again.

Steamhead

Another option

is to stage two or more smaller boilers as needed to meet the heating & hot-water load. Whether or not this is practical will depend on the load.

This might also be a good time to beef up the home's insulation, weatherstripping etc. Then you can install smaller boilers, which will use less fuel.

I don't think you can go wrong with any of the major boiler brands. A good boiler is a good boiler- it's the installation that counts.

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