View Full Version : mixing domestic h/w and hydro air
11-23-2006, 10:46 AM
my system uses a gas h/w heater for domestic with a tee in the line that provides h/w through the coil in the air handler. I have been told that this is wrong , but is it dangerous?
11-23-2006, 11:31 AM
Was it installed by a lic. contractor?
Was it inspected?
It also goes by the name of Apollo.
11-23-2006, 01:05 PM
The best way for this system to operate is with s special water heater that has 2 side taps for the hydronic coil and 2 top taps for domestic use. A standard 2 tap water heater will work, however, but not as well
11-23-2006, 01:23 PM
Is a check valve needed for that set up. We've worked on a few and have always wanted a check valve before the cir. pump.
11-24-2006, 02:11 AM
It's been a while since I've worked on them, but no I don't recall either a ck valve being required or recommended - I do recall however the need to for a tempering valve to control the domestic HW as the heater temp is set higher than a normal WH to keep the coil in the blower at a respectable temp.
I've attached the Webb site with the plumbing schematic.
11-26-2006, 09:18 AM
Haven't touched one of these in years, but remember something in the code requiring a cycle timer on the circ. to the air handler that will keep the water from stagnating in that line.
Quit even looking at this as an option once I'd done the research and realized just how inefficient water heaters are when used to produce heat.
A check valve would be a good idea, or one of the checked pumps if the air handler is above the water heater. Migration of hot water through the lines would probably be substantial. :) Might negate the need for a circulator timer though!
11-29-2006, 01:15 PM
I was wondering if you could provide some additional comment on the inefficiency of water heaters producing heat.
I have been considering an oil fired water heater (Bock) for my DHW and providing supplemental heat for two heat pumps. From my perspective the oil will provide much more BTU’s than the propane I currently use for heating my DHW and oil seems to be a more efficient method of supplementing heat pumps than electric strips. Please, tell me why this is not a good idea.
11-29-2006, 01:49 PM
This type of system is often seen in apartments where the domestic hot water and the space heating load are both low. My cousin lived in an apartment that had this setup. He said if he was in the shower and the tstat called for heat he ran out of hot water.
You need to use a bronze circulator and there is an issue with stagnant water sitting in your heating coil.
mchild- dom water heaters aren't rated with efficiencies. Most are in the 70% range. I can't imagine why you would want to install a new oil fired water heater. Do you have oil now? When calculating the cost of the oil tank, oil fired water heater (do you know how much they cost?), and annual cleaning I don't see how you can save money.
11-29-2006, 02:16 PM
Yes, I have oil now in addition to propane. My current propane water heater is ten years old so its time is not long.
Based on some preliminary cost estimates, the cost difference between the Bock water heater and the one I have now is about $400. The Bock unit seems to have a typically longer life than most water heaters so some premium on the price is warranted. The Bock unit is 80% efficient (125K – 140K BTU output), which is in line with oil furnaces. Therefore, if my supplement heat needs are 20% of my total heat loss (heat pumps provide the first 80%) then it seemed like a reasonable step to pull from the water heater for the supplement.
Apartment owners are notorious for under sizing HVAC equipment. I can see if the water heat was the only heat source and undersized to boot, then you could have problems with showers. Properly sizing the unit is important, but when it is and with 150o to 160o output temps it does not take much hot water for a shower.
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