really dumb hydo air ???????

Dave Palmer_3

dumb question, customer has a dead scorched air furnace and a electric 80 gallon W.H. I want to install a boiler with HWM and air-handler.Heat-loss for the house is 65,000btu's,can I use a smaller boiler to feed both because (assume) the temp of the airhandler would be lower then a furnace? thanks Dave Palmer

Big Ed

Boiler

Your largest load would be the indirect hot water heater.I'am assuming "HWM" is a indirect. You want to size the boiler for the largest load . You don't want to under size the boiler too much for it would take longer to heat the indirect.In the mean time your heat could be down if using a priority ....

kevin coppinger_4

a BTU is a btu....

regardless of the water temp. figure out the heat loss at the proper design temp. and then figure out your hot water demand. You can prioritize to the hot water but if you are right on the cusp of the max it might not hurt to go up to the next size ( w/in reason)...hth..kpc

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GEO_3

Double check your loads. You might be able to use a water heater with a heat exchanger. Or use potable water for everything if your coil is rated for it and your codes allow it.

Cosmo_2

Here we go

I was with you with the heat exchanger, but as a Master Plumber I have to vehementaly disagree with even suggesting someone using potable water in the hot water to air coil. I do not want to be impolite, but wether or not the codes allow it potable water should NEVER be used in a heating system that will sit idle for months at a time. No discussion as far as I am concerned..........

Cosmo

GEO_3

Thats why they make pump timers. All the potable water approvals I've seen require you cycle the pump daily. I'll agree there are some extra precautions you hace to take but it does make for a very economical system. Operating cost run 1/2 to 1/3 less than conventional boiler/ waterheater set up. The downside is waterheaters don't last as long as boilers. Although they do last longer with return circulation

Joannie

Also

Since this is not a new system, you may not be able to use a water heater for both hydronic and potable water heating.

The water heater certification standard, ANSI Z21.10.3, states:

"A water heater suitable for water (potable) heating and space heating shall bear Class IIIA markings indicating:
a. The water heater shall not be connected to any heating system or component(s) previously used with a nonpotable water heating appliance...."

Roger Litman

Domestic water

With priority and the fact that there are few days of design temperature in any area, the use of hot water will only use about 3000Btu per hour for 24 hours, so that WITH adequate storage only a small correction is needed(if at all) for domestic water in almost all residences. The heat loss will have to be covered and if you put in a significantly smaller system than the loss- then you are in deep trouble.One caution is that if the customer uses a strong level of setback temperature- then you will need more Btu to get a quick pickup of temperature.

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jw

Setback stat is a lifesaver

Had a combo setup that customer complained of no hot water. Asked him how he uses system. Said that heat was set back 10F at night. In morn, heat was turned up and five people took showers. Ouch! No wonder he had problems. Installed a setback thermostat for him so house would warm up one hour before waking. No more complaints!

GEO_3

The system was old but the coil/air handler was new. In this state[ Ma.} the equip has to be Board approved. First Co. had an approval and I'm sure others. These approvals included pump timers. Love to get everybody thinking.