Repair-It

I have an oil fired forced hot air furnace, single zone. It is possible to add a central air evaporator coil to it (and a condenser outside) and have central A/C at like half the cost compared to someone who has hot water baseboard heat. So that's cool.

But then I had a thought.

Can't I evolve that A/C idea into a heat pump? It is the same basic equipment. The system just now has the capability to run "backwards," warming the evaporator in cooler weather with heat from outside.

In the summer, it's simple. I just have central A/C. Great. I want that.

In the winter, the use case would go like this: in cool temps, maybe above 40°F, it would run as a heat pump. If that wasn't enough, the oil burner would kick on, probably shutting off the heat pump.

I believe this is well within reason, and the advantage is you don't have to worry about going to 100% heat pump in cold New England winters, at least with an air exchange condenser unit (geothermal heat pumps can work year round). Plus National Grid has a $500 rebate for heat pump systems vs $250 for just central A/C.

It hinges upon:
A) What is the profile of electricity use vs oil use vs temperature outside? (not to mention cost of each energy source), which leads to,
B) Return on investment. Presumably I will pay more for this solution just from a controls standpoint even though the equipment is basically the same,
C) That someone actually would retrofit my older hot air furnace with all this, instead of trying to sell me a brand new everything

I think this is interesting and I'd like to subscribe to my own newsletter.

I think this is interesting and I'd like to subscribe to my own newsletter.

Isn't that what Repair-It is?

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Please don't make this site send emails...
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Um... Gotta go.

I guess I took too many liberties in my paraphrasing.

https://m.youtube.com/watch?v=wlMwc1c0HRQ

That is pretty funny, and I was just kidding.

Frank is using an Air-sourced heat pump that is very similar to what you are describe in the couple of sentences I read.. So the technology exists.

He didn't have the oil-furnace part, but I suspect others have done basically what you are talking about.. Air-source heat pumps apparently struggle in very cold weather. Makes sense to me because the outdoor heat exchanger would have to be colder than the ambient... That would mean that in winter it would have to be well below freezing to gather any heat energy. So many homes probably add a conventional furnace to supplement the very cold days.

kevm14 wrote: It hinges upon:
A) What is the profile of electricity use vs oil use vs temperature outside? (not to mention cost of each energy source), which leads to,
B) Return on investment. Presumably I will pay more for this solution just from a controls standpoint even though the equipment is basically the same,
C) That someone actually would retrofit my older hot air furnace with all this, instead of trying to sell me a brand new everything

I think this is interesting and I'd like to subscribe to my own newsletter.

Frank did a spreadsheet that addresses #1. I'll leave it to him to make it public. Or I can email it to you.

Sure I could have two systems, but I thought there would be an efficient way to add central A/C by adding heat pump-capable equipment instead, and having some kind of smart controller that worked the whole deal, in a single system. Rather than having a heat pump system, and an additional oil furnace system. Besides, I only have one set of duct work so I don't even know how I could have two independent systems.

The operating assumption is that the heat pump is cheaper to operate as a heat source than oil, when prices are X and outside temperatures are Y. I don't know what the X and Y are.

kevm14 wrote:Sure I could have two systems, but I thought there would be an efficient way to add central A/C by adding heat pump-capable equipment instead, and having some kind of smart controller that worked the whole deal, in a single system. Rather than having a heat pump system, and an additional oil furnace system. Besides, I only have one set of duct work so I don't even know how I could have two independent systems.

I'm saying that you would have an air sourced heat pump system, but the indoor evaporator/condenser would be in you oil furnace venting. pretty much as you describe.