Sizing Mod-cons and Indirects

Joe@buderus_2

Some units, such as the Buderus GB142 have the option of "limiting" the firing rate of the boiler when in the heating mode (Buderus can be adjust down to 30%). If there is a large hot water demand the use of a larger than need mod boiler, proper size indirect, proper circulator and possibly the addition of a storage tank can work well, be efficient and not short cycle.

Wayco Wayne_2

I was talking

to a fellow today who said he sizes his boilers according to domestic water load rather than heat loss with mod con boilers. His contention was the boiler is modulates doesn't it. (Ack!) It didn't sit well with me and made me think. If the mod con is oversized you would be losing efficiency because you would be short cycling rather than modulating. Are the losses that great? What is another way to meet the domestic water load if it is larger than the boilers capacity. A larger storage tank? Have you guys run into this conflict of interest when sizing mod cons and what do you do? WW

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Todd_27

It depends

Good answer right? If they want tons of endless hot water then you have to have the btu's to drive it. If they want efficiency then its as small a boiler as possible. If its a combo of the two, I would try to oversize the tank and keep the boiler a little smaller. Just my .02cents