Condensing boilers for radiant heat and potable water?

Constantin

... and Viessmann makes a very, very nice one. However, whether or not the on-board storage is adequate to keep your house supplied with domestic hot water depends on the load it is expected to maintain.

One way to determine just how much water you need is to tally your bathrooms, usage patterns, etc. and then see how many gallons of domestic hot water that equates to. One low-tech way to do it is using a 5-gallon pail and a stopwatch in the showers to see just how much water they are passing, for example. Flow rates depend a lot on local water pressure, scaling, etc. conditions.

BTW, keep in mind that you can keep the storage tank at 140°F and then use a mixing valve to bring the output down to a safe temperature. Blending very hot water from the tank like this with cold water thus allows you to stretch the supply. Also, some contractors advocate keeping domestic hot water tanks at these temps to sterilize them.

Another inexpensive way to decrease the amount of heat that a boiler has to add to the domestic hot water is to reclaim the heat coming out of your shower, etc. See <a href="http://www.gfxtechnology.com">GFX Technology</a> for more on this. I have one GFX HX in the basement that serves the whole house, though other installations do innovative things like pre-heat the cold water going into a shower valve with the warm water coming out of the shower drain.

If you have multiple bathrooms, large shower heads, or worse, teenagers then the storage tank inside the combi units may be too small. However, until you tally it all up, you simply don't know. Good luck!

Brian_5

Condensing boilers for radiant heat and potable water?

I am looking into buying a condensing boiler for its high efficiency to use for a radiant heat system and instantaneous hot water for my house. Are there boilers out there that can do both of these tasks in one unit. I would hope it could produce at aleast 7 gpm of hot water for the potable side. And the radiant heating system would only be working in a large kitchen and bathroom. What systems are the best to handle this? and what manufacture makes the best boiler to do this? I have been told that the Viessman is the way to go? Any advice would be great. I am going to be firing this boiler with propane, the only gas available to me!

Narroc

cvincent@ihug.co.nz

> I am looking into buying a condensing boiler for

> its high efficiency to use for a radiant heat

> system and instantaneous hot water for my house.

> Are there boilers out there that can do both of

> these tasks in one unit. I would hope it could

> produce at aleast 7 gpm of hot water for the

> potable side. And the radiant heating system

> would only be working in a large kitchen and

> bathroom. What systems are the best to handle

> this? and what manufacture makes the best boiler

> to do this? I have been told that the Viessman

> is the way to go? Any advice would be great. I

> am going to be firing this boiler with propane,

> the only gas available to me!



To heat 7 galls of water per minute, you would need
7 x 10 x (160-60)x 60, =
420,000 Btu's per hour/3,412 = 123 KW

Were 1 Btu = 1lbs water 1 deg F,
10 = 10lbs per galls, 160 deg = assuming temperature of hot water
60 deg = asumming temperature of cold water,
60 = minutes in an hour, 3,412 bTU's = 1 KW.

123 KW is a fairly big boiler for a home, especially if your heating load is low, As it appears if you only going to heating a couple rooms,
I think you need to rethink on using storage hot water.
Most small combi boilers are around the 25-30Kw (85,300-102,360 BTU's)

Narroc

cvincent@ihug.co.nz

To heat 7 galls of water per minute, you would need
7 x 10 x (160-60)x 60, =
420,000 Btu's per hour/3,412 = 123 KW

Were 1 Btu = 1lbs water 1 deg F,
10 = 10lbs per galls, 160 deg = assuming temperature of hot water
60 deg = asumming temperature of cold water,
60 = minutes in an hour, 3,412 bTU's = 1 KW.

123 KW is a fairly big boiler for a home, especially if your heating load is low, As it appears if you only going to heating a couple rooms,
I think you need to rethink on using storage hot water.
Most small combi boilers are around the 25-30Kw (85,300-102,360 BTU's)

Constantin

No worries...

... any quality boiler can produce hot water for domestic use and heat spaces at the same time. Optimal boiler selection plus the balance of plant (BOP)depends in large part on the loads.

For example, it has been my observation that kitchens that are actually used need less heating due to stoves, ovens, etc. adding their BTUs to the room. In fact, my old rental apartment had radiators in every room but the kitchen... Bathrooms are another matter though, and warm bathrooms are a great luxury.

Narroc hit it on the head as far as the BTU requirements are concerned, particularly if the water load is continuous. In many situations however, the need is not constant and you can get by with a smaller boiler and a indirect water heater as a buffer. There are some very large buffer tanks out there and the best ones lose very little heat.

There are many manufacturers to choose from that make boilers, controls, and storage tanks. However, in my estimation the most important factor is the professional you choose to install the system. If you hire a great pro and keep up with the maintenance, then even a entry-level condensing boiler ought to serve you well. Such a pro would also be able to sit down and discuss your hot water needs in detail for equipment selection.

Considering your intended fuel and application, a condensing boiler looks like a great choice. I have had nothing but good experiences with Viessmann, so I am partial to the brand. While my Vitola may not be as energy-efficient as a Vitodens, it has been heating my home reliably and efficiently with the fuel of my choice, oil.

Brian_5

Thanks for the info Constantin. To get into further detail with what I am trying to do; I would like to use a wall hung direct vent unti like the Rinnai, I have been installing recently. (for potable) I was told by another heating professional that Viesmann makes a similar unti to the Rinnai but that it also allows you to so space heating as well. All in one unit.

From what you said it seems like you think it might be better to use a boiler and a storage tank rather than the system that I am describing. Is that right? If so, is that because the combo units I am talking about would not be able to handle the load for both potable and my radiant heat situation? Thanks for the advice.

What is your opinion on the best wall hung tankless water heater? I have been installing the Rinnai and so far seems pretty good.